Has anyone ever megged a multimeter ? (HV testing) - Page 1
Forum section: electronics / testgear

author: LinuxGuy123
author_rank: Regular Contributor
timestamp: January 22, 2025, 05:12:58 am
content: There is lots of talk about how some (less expensive, imported) multimeters are or could be dangerous for HV work.Has anyone ever connected a (cheap) multimeter to a HV source and tested its rating or purposely destroyed one ?

author: Kean
author_rank: Unknown
timestamp: January 22, 2025, 05:37:42 am
content: Oh boy, you have some catching up to do...https://www.eevblog.com/forum/testgear/hear-kitty-kitty-kitty-nope-not-that-kind-of-cat/https://www.youtube.com/@joesmith-je3tq/videos

author: LinuxGuy123
author_rank: Regular Contributor
timestamp: January 22, 2025, 05:51:57 am
content: This group never disappoints ! Excellent work.

author: joeqsmith
author_rank: Super Contributor
timestamp: January 22, 2025, 05:27:27 pm
content: Kean became an unintentional expert in this areahttps://www.eevblog.com/forum/testgear/hear-kitty-kitty-kitty-nope-not-that-kind-of-cat/msg1601299/#msg1601299

author: Kean
author_rank: Unknown
timestamp: January 24, 2025, 04:32:30 am
content: Good memory Joe!Gee, that was 6.5 years ago and I've not yet managed to repeat it. I've actually been fixing things quicker than damaging them lately.

author: bdunham7
author_rank: Super Contributor
timestamp: January 24, 2025, 06:07:45 am
content: Quote from: LinuxGuy123 on January 22, 2025, 05:12:58 amBlowing up meters is a common sport around here. Dave Jones posted a video long ago blowing them up (literally) with a huge capacitor bank.The problem with just using a Megger or low-energy HV source is that it isn't really testing what meters are most vulnerable to in real life, namely transients and high energy circuits. In fact, using a Megger or HVDC, the cheapest or most unprotected meters may actually outperform good meters because they don't have any devices that clamp overvoltages.I've attached a photo of is what is widely regarded as the worst of the worst cheap meters--although it theoretically has an infinite bang-for-buck ratio because the typical price was $0.00 at Harbor Freight. As you can see, the meter is rated for 250VAC but I have it connected to 1100VAC and other than being not very accurate, it doesn't fail in any way. I don't have my HV supplies set up on bench right now, but I previously connected a different version (the older, yellow ones that had 1000VAC/750VAC printed on them) and I was able to crank it up to 1600VDC and it just indicated the voltage without complaint. I would have gone to 2000 volts but the input divider was smoking a bit so I backed off. They only have a 1M input impedance so at 1600V that miniscule resistor is dissipating over 2.5W.A CAT-III/600V meter might be better and safer in every way but not do as well with those inputs because the input devices would start to clamp and dissipate heat. They're designed to withstand transients at much higher voltages but not necessarily continuous application of severe overvoltages. Good meters will also withstand full rated input voltage even if you select the wrong range, perhaps ohms, temperature or capacitance. There is a video somewhere of a Fluke rep demonstrating this using the very same HF meter that I have here. For home electrical in North America even this cheap Harbor Freight meter is unlikely to be the primary cause of any serious injuries even if used in service panels or outdoor wiring because single-phase 240VAC just doesn't pose the same hazards that three-phase high-energy installations do. If it blows up because you left it in ohms mode while testing your circuit breakers or left the leads in the amp jacks, you'll just get minor burns and flying shrapnel at the worst--maybe bit of molten metal in the eye. I would be more concerned about the atrocious leads and semi-sheathed connections than anything else.

author: Aldo22
author_rank: Super Contributor
timestamp: January 24, 2025, 09:49:12 am
content: Quote from: bdunham7 on January 24, 2025, 06:07:45 amExactly!And with a ZT-225, not even that happens.The sturdy structure alone with the fat, slightly elastic holster simply does not allow it to “blow to smithereens” (attachment).It is immune to incorrect setting of the selector.The only place where something could happen is the 20A input with ceramic fuse.But the circuit breakers are at 16A in our house. What comes first?Nevertheless, “cheap” DMMs are always eagerly discouraged here because they said to be “unsafe” and potentially deadly.Deadly for whom? For Fluke? I don't think so.And before you get into anything that requires electrician training, you should get electrician training.Then you'll know what tools and safety measures you need. That might not include a Zotek meter, but protective goggles, protective gloves, a second person...But for anything on this side of CAT II, I wonder what the point of these exaggerated warnings is?After all, this is an "electronics engineering" forum and not a lineman forum.

author: Zero999
author_rank: Super Contributor
timestamp: January 24, 2025, 11:53:55 am
content: Insulation testers apply a tiny current, typically around 1mA, which shouldn't damage a decent multimeter.

author: joeqsmith
author_rank: Super Contributor
timestamp: January 24, 2025, 02:57:20 pm
content: I look for meters that are electrically robust and care little about safety. Cost doesn't seem to be a factor as the $50 Fluke 101 was one of the most robust meters I have looked at to date. I personally want a meter that can survive some basic low level transients because I do experiment with electronics beyond the world of logic gates and ESD is a factor in my home.At least at my home, arc flash is of no concern. Someone once brought up fault currents and I took the time to measure them in my lab.https://www.eevblog.com/forum/testgear/trashy-meters-redux/msg4835948/#msg4835948Quote from: Zero999 on January 24, 2025, 11:53:55 amI had seen a few videos of people running such a test, claiming they were putting some high voltage across the meter but ignorant of the fact that the meter was loading down the supply. Viewers comment how great the meters are for surviving such a high voltage.My question is why does the vintage Fluke calibrator need such bling? My wife fixed up my whore of a scope. Maybe some nice hoop rings and gold chain would have augmented the look.

author: bdunham7
author_rank: Super Contributor
timestamp: January 24, 2025, 03:08:59 pm
content: Quote from: Aldo22 on January 24, 2025, 09:49:12 amI'm not going to sneak into your house at night and confiscate your meter, but I have some issues with those three statements.First, IIRC there is a Youtuber who tested the meter in ohms, etc at 220VAC. The meter is labeled, among other things, as "CATIII/1000V". Just to prove a point I put my old Fluke 27 in ohms mode and applied 1000VAC, photo attached. No harm done, meter is still fine. IDK, maybe your ZT-225 would do as well--or perhaps not. Would you try it? It's not just an explosion or fire issue, it's also a question of whether the meter is easily killed or not.Next, the "you shouldn't be doing that anyway" argument doesn't address the issue of whether a device meets the ratings that are printed on it. The OP clearly works with systems that have significant energy and didn't seem to be aware that some meters that are labeled as appropriate for that might not actually be up to the task. Some people would look at my old Fluke 27 which is labeled only CAT III/1000V and compare it with the newer ZT-225, which is additionally labeled CAT IV/600V, and then conclude that the newer meter with the additional rating is probably better. Zotek's own marketing repeatedly mentions the CAT ratings and claims it is an appropriate tool for "electricians and maintenancers". I'm not convinced.https://zotektools.com/products/zoyi-zt-225/

author: bdunham7
author_rank: Super Contributor
timestamp: January 24, 2025, 03:17:05 pm
content: Quote from: joeqsmith on January 24, 2025, 02:57:20 pmThe calibrator is standing up and since the face is now a horizontal surface, it accumulates stuff. That's a Timex watch that I'm suppose to fix someday.

author: joeqsmith
author_rank: Super Contributor
timestamp: January 24, 2025, 03:23:35 pm
content: If you place a second meter in parallel with the Fluke, do you actually get 1000VAC out of the calibrator? When you let the Fluke cool, then turn on the calibrators output, does it immediately read 1kV? I'm surprised it can drive that much current.

author: tooki
author_rank: Super Contributor
timestamp: January 24, 2025, 03:40:28 pm
content: Quote from: joeqsmith on January 24, 2025, 03:23:35 pmThedatasheetsays 6mA maximum.

author: Fungus
author_rank: Super Contributor
timestamp: January 24, 2025, 03:45:30 pm
content: Quote from: Aldo22 on January 24, 2025, 09:49:12 amGo watch a few more joesmith videos. There's quite a few where the meters jump around inside the box even on his low energy generator.Converting copper into vaporisan explosive process.Even if it doesn't kill you directly the fright of it going "bang" in your hand could easily make you fall off a ladder or something.

author: Aldo22
author_rank: Super Contributor
timestamp: January 24, 2025, 03:48:25 pm
content: Quote from: bdunham7 on January 24, 2025, 03:08:59 pmYou are welcome!Second option: Order one just to see what it can take.https://www.aliexpress.com/item/1005007244323221.htmlQuote from: bdunham7 on January 24, 2025, 03:08:59 pmI don't have a 1000V source myself, and to be honest, I'm about as interested in that as whether the DMM implodes at the bottom of the Mariana Trench.And with a DMM that costs as much as a Fluke fuse, I'm not interested in whether the DMM will break in (for me) unrealistic situations.Quote from: bdunham7 on January 24, 2025, 03:08:59 pmYes, but he OP also said in the other thread that he will continue to use his Agilent 1271A for the “dangerous stuff”.I also pointed out there that I would use a more professional tool than the Zoyi for his case (480VAC).Not necessarily because I think the Zoyi would kill him, but simply because I assume a different attitude to safety-related issues in these areas.But that's not really my point at all.Why don't you just say, “The ZT-225 is an incredibly great DMM for electronics hobbyists at a very reasonable price.If you think the meter might fall into the wrong hands, scrape out the CAT ratings and have fun measuring microvolts and nanoamps."

author: tooki
author_rank: Super Contributor
timestamp: January 24, 2025, 03:55:43 pm
content: Quote from: Fungus on January 24, 2025, 03:45:30 pmIndeed.Someone made a video about this very topic the other day:One nugget of info from it: in nuclear bombs, they don’t use chemical igniters to start the reaction because the timing is too imprecise. So they use exploding wire to time it to ns precision. It’s not the thermal effects, but the actual pressure wave from the exploding wire that is used to begin the explosions that ultimately compress the fissile material to criticality.Our resident multimeter anti-safety crusader, Aldo22, is absolutely correct that most people here do not need a meter capable of protecting users from high-energy discharges, since most forum users aren’t working on high-energy circuits. But I do think he wildly underestimates what high-energy circuits are capable of, and may not fully understand which circuits are actually high-energy enough to be problematic.

author: Aldo22
author_rank: Super Contributor
timestamp: January 24, 2025, 04:04:16 pm
content: Quote from: bdunham7 on January 24, 2025, 03:08:59 pmIn my case, I wouldn't need these CAT ratings on the Zoyi and perhaps it would be clearer to simply leave them out. You're right about that.It would still be the same useful device for me and we wouldn't have to have these irrelevant discussions all the time.

author: themadhippy
author_rank: Super Contributor
timestamp: January 24, 2025, 04:09:16 pm
content: If your gonna use a megger then at least use a megger thumper not a piddle little 1000v megger insulation tester

author: bdunham7
author_rank: Super Contributor
timestamp: January 24, 2025, 04:11:16 pm
content: Quote from: joeqsmith on January 24, 2025, 03:23:35 pmYes and no.I don't need actually need the parallel meter as the calibrator will shut off if it is overloaded and can't maintain the voltage. It's pretty good about that--it will display OL pretty quickly anytime the feedback loop isn't satisfied and then shut off the output if that continues for more than a few seconds.For initial output into a cold PTC it indeed cannot put out the 250mA or so that would take so I have to "walk it up" by heating the PTC in stages. I'll start at 200VAC and then turn it up over a 15-20 second period. I do have DC supplies that will put out enough of a surge that they can drive the meter directly at 1000VDC but they're not connected and ready right now. The result is the same, as one would expect. The clamps just have to be big enough to not blow up (or off the board) and the Fluke 27 uses "select" MPS6560 or similar transistors in a TO-92 case.

author: bdunham7
author_rank: Super Contributor
timestamp: January 24, 2025, 04:17:06 pm
content: Quote from: Aldo22 on January 24, 2025, 03:48:25 pmYes, he did say that after the issue was pointed out.QuoteWell I don't say it because that's your point. And if the meter wasn't labeled or said "not for electricians" or something like that, I'd have no objections. I do have meters and stuff on my bench that probably aren't protected any better than the ZT-225 but I do prefer stuff that doesn't blow up if I make a mistake. Bench PSUs that blow up if you connect a battery to them are my other pet peeve....

author: tooki
author_rank: Super Contributor
timestamp: January 24, 2025, 04:20:30 pm
content: Quote from: Aldo22 on January 24, 2025, 04:04:16 pmThere is widespread agreement here that we would welcome multimeter manufacturers being honest about little meters without CAT ratings. There is absolutely a place for those meters.What is inexcusable is lying about CAT ratings, because it could put someone in danger, for example if some unwitting buyer at a power company buys fake-CAT-rated meters for the company’s linemen who actually are working on dangerous high-energy circuits. The fake paper trail makes it seem the meters are suitable, and the guys using them are at serious risk if something goes wrong. Those meters might have been perfectly safe for 99% of buyers, but not for those linemen.

author: joeqsmith
author_rank: Super Contributor
timestamp: January 24, 2025, 04:23:27 pm
content: Quote from: Fungus on January 24, 2025, 03:45:30 pmCorrect and was the basis for my model rocket.

author: Aldo22
author_rank: Super Contributor
timestamp: January 24, 2025, 04:39:01 pm
content: Quote from: tooki on January 24, 2025, 04:20:30 pmWell, the fact that the budget meters do not comply with their declared standards would have to be proven in individual cases.It is usually simply assumed in this forum.I don't know enough about it.But yes, as Dave Jones said, the CAT I and II declarations on the front of a meter will be removed in future anyway. That would be a good opportunity to do away with dubious CAT ratings completely.Personally, I am interested in other things, such as accuracy and precision/resolution, measuring range etc. etc.I have never bought a DMM because of CAT ratings.

author: joeqsmith
author_rank: Super Contributor
timestamp: January 24, 2025, 04:55:14 pm
content: Quote from: bdunham7 on January 24, 2025, 04:11:16 pmI will test them with DC based on what ever they claim the meter can handle (normally 600 or 1kV). But I only do this with the meter set to DCV and I slowly bring them up. To date, this has never cause any meter to fail. No surprise.The homemade transient generator does have a 220V transformer which I run through a full wave rectifier and apply to the meter with them set to each mode. The transient generator measures the current through the meter and will turn off if it gets too high. The only time it trips is when I have demonstrated this circuit by shorting the output or driving something like an incandescent bulb as a load. This simple test has damaged six meters to date.I also perform a 1kV transient test. I would expect every meter would pass this but six of them have failed. They don't like that fast edge. I have a kV supply that can easily output enough current that it will not droop when driving a meter, but I don't use it as part of my testing. My guess based on the 1kV transient tests, there are meters out there it would damage.As a hobbyist, and a cheap one at that, I am also interested in if I can repair the meters after they are damaged. Someone recently posted how I am able to repair the majority of them. Actually, the majority are damaged beyond repair. Some, like that crappy, expensive Keysight use custom parts that are not protected. Once damaged, good luck finding parts. Many of the < $100 use COB which are often damaged.IMO, the worse meters are the ones that cost >$20 that can't survive a basic ESD pulse. The free meters from HF will not survive much of anything but they are free with purchase. They are on par with my first Fluke meter.

author: joeqsmith
author_rank: Super Contributor
timestamp: January 24, 2025, 05:07:08 pm
content: Quote from: Aldo22 on January 24, 2025, 04:39:01 pmFor home use, same. I could care less about 61000 safety. I want something that survive 61326. The accuracy, ..... other specs, I have to trust the manufacture to meet what they claim as I have no way to test them for calibration. Still, I don't recall seeing any meters that appeared to be far out of spec when I do my basic checks.

author: tooki
author_rank: Super Contributor
timestamp: January 24, 2025, 05:09:56 pm
content: Quote from: Aldo22 on January 24, 2025, 04:39:01 pmNo, it isn’t just assumed.When you see a meter with a 250V AC 5x20 (or 5x10!) glass fuse, you know it is by definition not compliant. When you see one with no fuse at all (on the current ranges), you KNOW it isn’t compliant! When you see a meter with input PCB traces with a screw running between them, using up all of the space between the traces (such that it is almost shorting them out) you know there is no way it could pass CAT rating testing. When you see a meter that explodes when subjected to the CAT rating’s test conditions, you know it isn’t compliant.There do exist properly CAT-rated meters without fuses: meters without current ranges.I mention fuses a lot because they’re an easy first sign of… effort. Do you think the big manufacturers would use cheaper fuses if they could, and still meet the stated rating? Of course they would. It’d be cheaper for them and less annoying for users. So the fact that the big names use the $$$ fuses is a strong indicator that the CAT ratings cannot be met without those fuses.But it’s not just fuses: if a meter lacks real input protection, it’s not likely to meet CAT ratings. Again, we see what the big names do (adding things like gas discharge tubes and other overvoltage devices), which the cheap brands leave out, and which the big brands would leave out if not necessary.And there are meters that, regardless of CAT rating printed on them, do clearly make more effort than others, because of using better fuses (like British-standard ceramic mains fuses), and having decent input protection otherwise.Quote from: Aldo22 on January 24, 2025, 04:39:01 pmWhich is why it’s really, really annoying that you keep inserting yourself into those discussions, declaring that everyone else is exaggerating the risks. You don’t know nearly enough about the subject to be lecturing everyone else about it!Your ignorance is not of equal value as others’ expertise!!Quote from: Aldo22 on January 24, 2025, 04:39:01 pmIt’s bizarre to me that they decided to eliminate the lower categories. :/Quote from: Aldo22 on January 24, 2025, 04:39:01 pmHow would it? The problem is that cheap meter makers always slap either CAT III or IV on meters, even ones that very obviously cannot meet those ratings.Quote from: Aldo22 on January 24, 2025, 04:39:01 pmAnd that is absolutely fine. But it’s irresponsible to tell everyone else here that they don’t need to observe CAT ratings either, and it’s absurd to basically insult people who try to take a more nuanced position.

author: bdunham7
author_rank: Super Contributor
timestamp: January 24, 2025, 05:12:43 pm
content: Quote from: Aldo22 on January 24, 2025, 04:39:01 pmIt isn't just simply assumed, or at least it wasn't until there were plenty of examples and evidence. Then there appears to be some differences in how those standards are interpreted, specifically whether the requirement is that the meter simply not blow up or whether it should continue to operate. Certain manufacturers have shown specific contempt for the standards by simply omitting the relevant components when selling the meters in markets where there is little inspection or enforcement or by selling the exact same meter in one jurisdiction with much higher ratings then ones sold somewhere that cares. Others have been found to have submitted samples for certification and then selling meters that aren't not manufactured as the samples were. So if CEM, Uni-T, Zotek or whoever print a CAT rating on their meter I'm not going to give them the benefit of the doubt.And old thread discussing this, with examples:https://www.eevblog.com/forum/testgear/a-list-of-multimeters-that-do-not-appear-to-meet-their-claimed-safety-specs/msg157700/#msg157700

author: Aldo22
author_rank: Super Contributor
timestamp: January 24, 2025, 05:23:24 pm
content: Quote from: tooki on January 24, 2025, 05:09:56 pmI am not insulting anyone.I just think that CAT ratings are irrelevant for most electronics hobbyists and that a budget meter can have other advantages and you shouldn't reject these devices simply because of their (dubious) CAT ratings.And I also clearly stated that you should buy professional gear beyond CAT II.Let's not get carried away.

author: tooki
author_rank: Super Contributor
timestamp: January 24, 2025, 05:47:30 pm
content: Quote from: Aldo22 on January 24, 2025, 05:23:24 pmSuggesting that being concerned about safety is “FUD”, and insinuating that everyone who concerned themselves with safety was spreading it, could certainly be interpreted as insulting:Quote from: Aldo22 on December 26, 2024, 11:09:14 amAnd before that you said:Quote from: Aldo22 on December 26, 2024, 10:19:48 amThose are some bold statements from somebody who doesn’tQuote from: Aldo22 on January 24, 2025, 04:39:01 pm

author: joeqsmith
author_rank: Super Contributor
timestamp: January 24, 2025, 05:57:46 pm
content: Quote from: Aldo22 on January 24, 2025, 05:23:24 pmQuote from: Aldo22 on January 24, 2025, 09:49:12 amI have never attempted to blow a meter to smithereens. When designing the transient generator I use to evaluate the meters, I purposely limited the amount of energy (again, I was never interested in safety). I have seen some meters that will breakdown during my testing or supplied with glass fuses. For these special meters, I will apply the HV transient (enough to cause the meter to arc and develop a low impedance path) and then inject enough energy to simulate a half cycle of AC (about 600J max). Not a lot, but enough to provide some idea of what could happen.It would be interesting to see an accredited lab run independent tests on meters. Till that time comes, I guess take what I show for what it is. All meters tested to limited low energy sources.

author: Aldo22
author_rank: Super Contributor
timestamp: January 24, 2025, 06:06:40 pm
content: @tooki: Please calm down a bit. It's not that important, is it?Maybe I have no idea, but Dave Jones is heading in the same direction:Quote from: EEVblog on October 29, 2024, 04:14:20 amAnd by the way, have a nice evening!I have to go now.

author: joeqsmith
author_rank: Super Contributor
timestamp: January 24, 2025, 07:22:53 pm
content: Is Dave the gold standard for all advice?

author: Gyro
author_rank: Super Contributor
timestamp: January 24, 2025, 07:38:39 pm
content: I really hope not!

author: tautech
author_rank: Super Contributor
timestamp: January 24, 2025, 07:42:18 pm
content: Quote from: joeqsmith on January 24, 2025, 07:22:53 pmCertainly not.The standards are.My last hobby DMM purchase was a Fluke 15B that does all I need and has provided many years of service.Fluke 106 were given to my 2 sons last Xmas and I know that investment will protect them.....

author: bdunham7
author_rank: Super Contributor
timestamp: January 24, 2025, 10:15:46 pm
content: Quote from: themadhippy on January 24, 2025, 04:09:16 pmhttps://www.megger.com/en-us/products/ez-thump-12-kv-model-v3-cable-fault-location-systemI especially like the arc-reflection TDR feature! Now imagine you've left your DMM connected on the other end when you "thump" the cable.

author: joeqsmith
author_rank: Super Contributor
timestamp: January 24, 2025, 10:46:37 pm
content: Quote from: bdunham7 on January 24, 2025, 10:15:46 pmI doubt many typical CAT III/IV rated handheld meters would survive. 500J is on par with my low voltage generator but at 12kV, that's a lot of stress. Try it with your meter of choice and report back....

author: Sensorcat
author_rank: Regular Contributor
timestamp: January 25, 2025, 02:00:17 am
content: Quote from: Aldo22 on January 24, 2025, 09:49:12 amThis nonsense-assertion (in more than one way) alone is the proof that you should stop spreading your new religion over the forum!The real danger is this:The usual beginner that asks for DMM-selection advice starts like "I need a DMM, what should I take for my work, primarily Arduino stuff?" Means: "I do not exclude anything, just want to mention what I usually do." Being bold after a while, having developed impressive half-knowledge on Arduino stuff, he thinks that an electrician is no longer needed for fixing stuff in his house. It's the same kind of being bold with half-knowledge that makes YOU, Aldo22, lecture professionals on safety matter.

author: Aldo22
author_rank: Super Contributor
timestamp: January 25, 2025, 08:45:35 am
content: Quote from: joeqsmith on January 24, 2025, 07:22:53 pmYes, of course!No, but what he writes here sounds sensible, balanced and comprehensible.I'm sure the professionals here actually know that, but don't admit it for various, probably well-intentioned reasons.

author: tggzzz
author_rank: Super Contributor
timestamp: January 25, 2025, 09:46:11 am
content: Quote from: Aldo22 on January 25, 2025, 08:45:35 amSoundingthat way is completely insufficient.As tautech pointed out, the published standards are the appropriate source.One characteristic of such standards and codes of practice is that they often contain sections that appear bizarre and/or irrelevant. That's because they reflect whathasbeen asubtleand/orrareproblem in the past. They appear bizarre/irrelevant because the reader doesn't know/imagine/understand the problem. Another classic example of that phenomenon is disconnecting protective mains earth when floating a scope.It is reasonable and acceptable to be ignorant of thereasonsstandards/codes are the the way they are. It is not acceptable to push the line that the standards are unnecessary in some way.

author: pryce64
author_rank: Contributor
timestamp: January 25, 2025, 12:39:09 pm
content: Afternoon,Not sure why you would megger a DMM.Part of my role is we megger electronic equipment used in rail traction equipment.You first megger between vehicle earth and battery +ve and -ve record readings, then you apply high voltage flash test then you re megger.I have seen a AVO 8 meter blown to bits by sticking it across to high of a voltage and the noise was impressive.Built megger and flash ATE system to check RS485 cable on Class 390 tilt trains, no train was harmed.

author: tautech
author_rank: Super Contributor
timestamp: January 25, 2025, 01:40:43 pm
content: Quote from: pryce64 on January 25, 2025, 12:39:09 pmHow high ?AVO's typically had 2.5 or 3kV max ranges and were subject to a standard 7kV flashover test.

author: m k
author_rank: Super Contributor
timestamp: January 25, 2025, 02:11:11 pm
content: Quote from: joeqsmith on January 24, 2025, 05:57:46 pmI've not seen it, but I've seen results after mains connected electronics testing.Back in the day the machine was burned if it didn't include an accepted report of used materials and their smoke properties.With accepted report it was still partially burned using overvoltage to see how it ignites.In case the machine included safety features, like preventing overloading, all of those features were bypassed and tested again.If memory serves the minimal amount needed was three machines.The entity behind those tests was the old "FI" approval sign ratifier, like "S", "N" and "D" for other nordics.Compared to "CE" those old signs were real approvals.

author: pryce64
author_rank: Contributor
timestamp: January 25, 2025, 04:26:03 pm
content: How high,Not sure, I refused to get involved with AVO 8 as this was the first meter i used back in 1978 at my uncles radio and tv shop where i served my time(good old valve days).I was quite surprised to see them at GEC Trafford Park in 1992 and when used they where used for speedometer to read current output 0-5mA as some trains used moving coil meters.I am almost certain the occasionally put two in series to read higher voltages not sure who gave them that idea.

author: bdunham7
author_rank: Super Contributor
timestamp: January 25, 2025, 04:40:26 pm
content: Quote from: tggzzz on January 25, 2025, 09:46:11 amWhy? Is there some public policy restriction on what we're allowed to say? I see no issues with simply pointing out that arc-flash is not a household hazard.

author: pryce64
author_rank: Contributor
timestamp: January 25, 2025, 05:17:19 pm
content: Disagree,Arc-flash is a household hazard, to the hobby welder as me and our Niel found out while trying to weld a FIAT 500 floor pan in without using a shield back in 1980 and ending up in A&E(hospital).

author: joeqsmith
author_rank: Super Contributor
timestamp: January 25, 2025, 05:29:14 pm
content: Quote from: bdunham7 on January 25, 2025, 04:40:26 pmJust to be clear, I could care less about surge or fault currents when working at home.Quote from: EEVblog on October 29, 2024, 04:14:20 amThe above suggests that people who do work in industrial environments only need to be concerned with placing the leads into the Amps jacks and measuring current.Quote from: EEVblog on October 29, 2024, 04:14:20 amThe above suggests that in an industrial environment, the only source of high energy over loads is lightning. While I am not an electrician and do not work in a factory, even my limited exposure to what goes on around the world suggests both statements are false.When I wrote:QuoteI suspect that low voltage transient generator I designed could be applied directly to ANY handheld DMM I have evaluated, and nothing would happen. The reason is the voltage it puts out is so low, it is within the working range of products I have looked at. The damage comes from a meter that breaks down, or arcs. The low impedance path basically shorts the low voltage generator. It doesn't take a lot of energy to get a meter to break down. I test at less that 20J.Point being that we really don't even need a high energy, high voltage transient to start such a reaction. Any transient that caused a DMM to arc is good enough.While I harp on people who claim my testing is about safety, it is hard to ignore that if you have a meter that breaks down at low voltages, it could present a problem. Again, not at home, or at least my home. Again, look at that fault current data I provided for my lab. But in an industrial environment where arc flash is possible, I personally wouldn't use such a meter. Sound like Dave along with a few others, see it different.

author: joeqsmith
author_rank: Super Contributor
timestamp: January 25, 2025, 05:36:14 pm
content: Quote from: pryce64 on January 25, 2025, 05:17:19 pmI am interested in details about what happened in your specific case?

author: tggzzz
author_rank: Super Contributor
timestamp: January 25, 2025, 05:44:46 pm
content: Quote from: bdunham7 on January 25, 2025, 04:40:26 pmIs there a "public policy restriction" on telling inexperienced people that it is OK to run or walk into a road without looking? Would anybody regard it as acceptable to tell a child that?It must be OK, since I've walked into a road without looking and haven't come to any harm (yet).

author: bdunham7
author_rank: Super Contributor
timestamp: January 25, 2025, 05:46:02 pm
content: Quote from: pryce64 on January 25, 2025, 05:17:19 pmPerhaps that term means something different to you than it does to me.https://en.wikipedia.org/wiki/Arc_flashA welding suntan (or burn) is a different occasion, although arguably due to similar causes.

author: joeqsmith
author_rank: Super Contributor
timestamp: January 25, 2025, 05:55:08 pm
content: Quote from: bdunham7 on January 25, 2025, 05:46:02 pmSo you think he is suggesting that the arc as a result from welding and a bit of sun burn is what he is referring to as an arc flash? It could be. The arc blast from it would do much. At least, I have never felt any sort of pressure wave while welding.

author: bdunham7
author_rank: Super Contributor
timestamp: January 25, 2025, 05:59:31 pm
content: Quote from: tggzzz on January 25, 2025, 05:44:46 pmA hard core Darwinist, perhaps?QuoteYou're conflating a case with a known serious hazard (motor vehicles on the road) with a case where I'm claiming the hazard (arc-flash at home) is non-existent.

author: Gyro
author_rank: Super Contributor
timestamp: January 25, 2025, 06:01:00 pm
content: Quote from: joeqsmith on January 25, 2025, 05:36:14 pmHe means they were using an arc welder (controlled arc)) at close range (car floor pan) without skin or eye UV protection - with very predictable results. Not what we mean by arc flash in the electrical sense (uncontrolled arc current fault event).Edit: Doh, didn't notice the page turn.

author: tggzzz
author_rank: Super Contributor
timestamp: January 25, 2025, 06:08:56 pm
content: Quote from: bdunham7 on January 25, 2025, 05:59:31 pmMy response to that has already been stated -- in the context you carefully snipped, viz....Quote from: tggzzz on January 25, 2025, 09:46:11 am

author: Aldo22
author_rank: Super Contributor
timestamp: January 25, 2025, 06:19:44 pm
content: How many multimeter accidents and fatalities are there per annum?Are there any statistics?

author: Gyro
author_rank: Super Contributor
timestamp: January 25, 2025, 06:31:20 pm
content: Quote from: Aldo22 on January 25, 2025, 06:19:44 pmGosh, I wonder. Maybe Google (well maybe, a search engine that doesn't harvest your personal data) might be your friend.My first hit:https://www.progarm.com/news/number-of-arc-flash-incidents/Second hit:https://www.conney.com/websphere/ResourcesTabs/Knowledge-Base/Whitepapers/ArcFlash_Whitepaper.pdfThird hit:https://safearc.co.uk/services/arc-flash/2023-reviewYou get the idea.

author: tautech
author_rank: Super Contributor
timestamp: January 25, 2025, 08:40:03 pm
content: Quote from: Aldo22 on January 25, 2025, 06:19:44 pmWho cares ?At the tender age of 13 I was nearly one, 'volted' across the room using an old MC meter my dad made.We owe it to our consciences, present, past and future readers to only recommend DMM's that adhere to a Standard that matches our intended use.That it also might last for decades if well built becomes a bonus, regardless of cost.

author: tggzzz
author_rank: Super Contributor
timestamp: January 25, 2025, 09:01:51 pm
content: Quote from: Aldo22 on January 25, 2025, 06:19:44 pmFor that question to make any sense, you should provide your answers to this question...For X avoidable fatalities and Y avoidable serious injuries, what are acceptable values of X and Y?Alternatively, see tautech' reponse.

author: floobydust
author_rank: Super Contributor
timestamp: January 25, 2025, 09:06:39 pm
content: Aldo22 you keep shilling for the ZT-225 and I notice it has no certifications.Other Zoyi and ANENG etc. sometime have 61010 like this ZT-219 attached certificate. Those skilled in the art will enjoy the path to common fraud. Wow they went through all the hoops to certify at the 3,000,000uV level very impressive. Anbotek seems to be a joke agency. If you could please stop shilling for products that are untested for safety, that would be great.Multimeter injury lawsuits usually get settled out of court making it hard to find them, but people do get injured. They are kept out of the press.Going after a chinese manufacturer or USA dealer is not possible in the legal proceedings I've followed.One aspect of megger or hi-pot testing, it can be a problem using a steady high voltage test with long test times causing ozone buildup. This will cause arcing at a much lower voltage that just air. You'll notice transient testing voltages and 1-minute hi-pot test voltages are different, to test the same insulation.Hi-pot testers I commonly use them to a few kV but "burn-through" 95mA ratings quite high, so if there is an insulation failure it's now burnt, carbon so you can find it.

author: bdunham7
author_rank: Super Contributor
timestamp: January 25, 2025, 09:41:53 pm
content: Quote from: floobydust on January 25, 2025, 09:06:39 pmIf it had one would you be OK with using it on 480V 3PH?QuoteIn the CEM/Southwire example I posted a while back neither company was ever held to account. However, I wouldn't count on the same result in every case and jurisdiction.https://www.eevblog.com/forum/testgear/hear-kitty-kitty-kitty-nope-not-that-kind-of-cat/msg3714598/#msg3714598

author: floobydust
author_rank: Super Contributor
timestamp: January 25, 2025, 10:07:49 pm
content: It's all fine until somebody loses an eye or a hand etc. So far it's been the employer that pays the costs. Nobody cares about makers.On 480VAC systems I use Fluke with no tragedy.china can and does OEM build multimeters with certifications that pass "real" 61010 approvals, it will cost you more.They could make something decent, it's just that there is no need to do so. EV use will require better than what we've been getting due to HVDC I believe.Gifted a DT830d (board says 832d) from Taiwan "Cat. II 600V" (4kV transient) and of course took it apart to cringe at the spacings... but according to Aldo22 it's safe.edit: I see Suzy did great soldering that day.How much of a millimeter is everyone OK with in the red section I marked? (never mind the rotary switch spacings)I would say Joe's work and OP's intentions have use, until the chinese quit being fraudulent.

author: Kean
author_rank: Unknown
timestamp: January 26, 2025, 04:19:47 am
content: Quote from: floobydust on January 25, 2025, 10:07:49 pmAnd what were they thinking with the placement of that fiducial with a copper ring around it.

author: Fungus
author_rank: Super Contributor
timestamp: January 26, 2025, 07:08:26 am
content: Quote from: floobydust on January 25, 2025, 09:06:39 pmWeirdly enough: This one says "4.5V" on the certificate.3V, 4.5V ... where have I seen numbers like that before?Maybe the line you're looking for on the cert is the one that says "Test standards: EN61010-1".

author: Aldo22
author_rank: Super Contributor
timestamp: January 26, 2025, 09:26:59 am
content: Quote from: tggzzz on January 25, 2025, 09:01:51 pmSafety is always relative and should always consult common sense.Do you put on safety goggles, a helmet and fireproof clothing when you're frying up some chicken wings in the kitchen? Why not?It could splash hot fat into your eyes.A pot could fall on your head.Probably not, right?It is legitimate and not cynical to ask how statistically likely a danger is and how bad the consequences are if it happens.There are statistics for this purpose.In my small country, there is an average of 1.3 deaths per year due to electric current at work.Sure, that's 1.3 deaths too many, but it's questionable whether this basic level can be improved.These are mainly accidents on construction sites (rough tools), rather than in connection with electronic tools.Here are a few comparative statistics from my country to help you put this into context.Example from 2017Fatalities due to sports accidents: 132Disabled due to sports accidents: 222Seriously injured due to sports accidents: 14,658Moderately seriously injured due to sports accidents: 38,430Fatalities due to accidents at home and during leisure time: 2032Of course, you have to do everything you reasonably can to avoid accidents, but you have to be realistic about the risk.As it looks, DMM deaths are almost impossible to record statistically.

author: tggzzz
author_rank: Super Contributor
timestamp: January 26, 2025, 10:33:18 am
content: Quote from: Aldo22 on January 26, 2025, 09:26:59 amThose raw numbers do not inform the debate. At the very least they should be normalised to either the population at risk or the number of hours doing the risky activity. If that's too abstract, consider how many people "do sport" and how many people "measure mains voltages with a handheld meter".After that, for your question to make any sense, you should still state what you to be acceptable values of X and Y.BTW, I am not against risky activities. As I've mentioned elsewhere, I have done and encouraged my child to do things which many regard as risky. That's because thebenefits have outweighed the controlled risks.I struggle to see thebenefitsof using meters that are inadequate for the job.

author: Aldo22
author_rank: Super Contributor
timestamp: January 26, 2025, 11:03:01 am
content: Quote from: tggzzz on January 26, 2025, 10:33:18 amThat's true, but these figures don't exist.Quote from: tggzzz on January 26, 2025, 10:33:18 amThis is a purely moralizing question, you can also ask it about sport, etc.It doesn't help.Quote from: tggzzz on January 26, 2025, 10:33:18 amI never said that. I just think that you don't necessarily need an officially tested CAT IV 1000V meter to measure an AA battery.I've always said (including in this thread) that you should use professional tools above CAT II.My point is just to classify the danger and compare it to other life risks. That sometimes seems a bit unbalanced to me here.

author: tggzzz
author_rank: Super Contributor
timestamp: January 26, 2025, 11:27:12 am
content: Quote from: Aldo22 on January 26, 2025, 11:03:01 amIn that case your contention that started this subthread is meaningless.QuoteMorality is a strawman argument; not being diverted.Youare the one that started down the route of arguing statistical importance. Either you back out of that route (sensible IMHO) or you follow the consequences.QuoteThat's a weird contention in the context of this thread, which is applying high voltages to meters.QuoteWelldocompare it to other life risks! Your figures have carefully avoided doing that.You can't ignore the benefits in a risk-reward setting.I backpacked around India with my early teens daughter; definitely not risk-free, but she benefitted by learning a hell of a lot that has proven invaluable later in life. Naturally she accused me of wrapping her in cotton wool, but later had the good grace to realise I hadn't

author: tooki
author_rank: Super Contributor
timestamp: January 26, 2025, 11:38:12 am
content: Quote from: Aldo22 on January 26, 2025, 11:03:01 amThat is most certainly not true. You keep pushing the ZT-225, which is neither a professional tool, nor CAT rated (no matter what they print on the front panel). Teardowns show it uses little 5x20mm fuses, which are not capable of the voltages the meter is specified for.

author: tggzzz
author_rank: Super Contributor
timestamp: January 26, 2025, 12:17:23 pm
content: Quote from: tooki on January 26, 2025, 11:38:12 amThanks for digging that out. I suspected it was true, but couldn't be bothered to disinter the evidence.

author: Aldo22
author_rank: Super Contributor
timestamp: January 26, 2025, 02:16:57 pm
content: Quote from: tooki on January 26, 2025, 11:38:12 amWhere did I say that the ZT-225 is the right device for CAT III/IV?I never said that. I'm not interested in that because I'm not trained for it.And yes, I also think that fake CAT ratings are a bad thing.Basically the only point where we disagree is that I think ZT-225 or AN870 are good meters for low voltage applications.You, on the other hand, think that anything with dubious CAT ratings is unacceptable from the start, if I have understood that correctly.OK, that's two opinions.Can we say "We agree to disagree"?

author: BradC
author_rank: Super Contributor
timestamp: January 26, 2025, 02:34:09 pm
content: Quote from: Aldo22 on January 26, 2025, 02:16:57 pmI use my AN870 for three phase 415V measurements. But then I also jaywalk, cross against a red light and terminate live mains, so I'm told I'm a bit "fast and loose" with safety.

author: tggzzz
author_rank: Super Contributor
timestamp: January 26, 2025, 02:39:38 pm
content: Quote from: BradC on January 26, 2025, 02:34:09 pmWhatbenefitdo you get from taking those risks?Do the benefits outweigh the potential penalties?Should you tell other people "I do X and haven't come to harm, therefore you can too"?Fundamentally I don't care what you do to your body. I don't even mind paying for your medical treatment.I do care what you do/encourage others to do with their body - or worse a third parties' body.

author: BradC
author_rank: Super Contributor
timestamp: January 26, 2025, 02:46:35 pm
content: Quote from: tggzzz on January 26, 2025, 02:39:38 pmNone at all. In reality they're all pretty high risk low/no reward sort of activities. I don't encourage other people to follow my lead, in fact I usually point out the danger in what I'm doing / about to do. More "do as I say, not as I do".

author: armandine2
author_rank: Frequent Contributor
timestamp: January 26, 2025, 03:50:53 pm
content: Quote from: LinuxGuy123 on January 22, 2025, 05:12:58 amNot to test the cheap dmm's rating , but the trivial "test" measurement, which everyone who has a multimeter and insulation tester does.

author: pryce64
author_rank: Contributor
timestamp: January 26, 2025, 05:21:27 pm
content: Afternoon,We thought we could weld floor pan with a stick welder converted to and arc welder by means of an attachment which had two carbon rods which you adjusted to cause an ARC which you used to braze two metals together.Lots of ointment from the hospital for eyes.I do how ever under stand why you should test DMM for use on high voltage's, our company test all our equipment once a year in house and also a external contractor also checks all our equipment and has a certificate stuck on the equipment fit for use.you still cannot ensure persons do not misuse or connect wrong cable's which do not meet the voltage or current ratings required.I have only seen high voltages/current measured using CURRENT MONITORING DEVICE or VOLTAGE MONITORING DEVICE and are designed to withstand 1000V to 4000V , 4000V = 10V also step down voltage to safe level.The ARC i have seen is when a air powered switch is closed, Shield or box around the contact assembly, switch closed by the toe touching and then roles back to the heal making full contact.Never thought to be anywhere near this equipment or have anything connected to it.Maximum voltage worked on is Vacuum circuit braker for pantograph on trains 46000V, and we used a gamma detector stand well back.

author: tooki
author_rank: Super Contributor
timestamp: January 26, 2025, 05:32:30 pm
content: Quote from: Aldo22 on January 26, 2025, 02:16:57 pmUmmm… you just said:Quote from: Aldo22 on January 26, 2025, 11:03:01 amSo you’re claiming that you only recommend using “professional tools above CAT II”, but repeatedly recommend a multimeter that can’t meet any CAT rating. And it’s fine to recommend it for low-voltage stuff, but don’t claim you’re only recommending meters with high CAT ratings, because that one doesn’t have it. (No matter what its front panel says.)Quote from: Aldo22 on January 26, 2025, 02:16:57 pmI never said those meters are bad for low voltage (or rather, for low-energy* use). I even own an Aneng (Zotek-made) AN8008 alongside my Fluke, Keithleys, and Keysights.At the same time that I think those meters are very acceptable for low-energy circuits, I still wholly condemn the manufacturer for lying about the CAT ratings.*I am not certain that you’ve fully understood that voltage isn’t the only factor, and that what matters is how much energy a circuit has behind it; that’s the thing the different CAT ratings really deal with.

author: Aldo22
author_rank: Super Contributor
timestamp: January 26, 2025, 05:52:14 pm
content: Quote from: tooki on January 26, 2025, 05:32:30 pmYou misunderstood or I didn't express myself clearly.I meant that forapplicationsabove CAT II you should buy a professional tool and - more importantly - have the appropriate training.This implies thatI do not classify the Zotek tools as professional tools.But they are good low-energy hobby multimeters.I wish Zotek would write CAT II 600V or something like that on them, then we could talk about the benefits of these meters and not have to talk about higher CAT ratings that are irrelevant for my use (and probably most - say - Arduino hobbyists).Is that more understandable now?

author: Aldo22
author_rank: Super Contributor
timestamp: January 26, 2025, 06:54:10 pm
content: Quote from: tooki on January 26, 2025, 11:38:12 amJust a small note to clarify this: These fuses are only for the A and mA/uA inputs.These are labeled Max 250V. So that should be correct.

author: bdunham7
author_rank: Super Contributor
timestamp: January 26, 2025, 08:42:09 pm
content: Quote from: Aldo22 on January 26, 2025, 06:54:10 pmThere's a lot of fur flying over the interpretation and application of a standard that we (I at least) don't have a current copy of. So I'm not really willing to accept that I should just respect the standard (as interpreted by?) and not discuss these things. Your statement is an example of something where 1) I think your interpretation is wrong 2) the standard may or may not be clear on this and 3) it is definitely worthwhile to discuss the common-sense reasons behind things no matter how ignorant we may all be. Well me, anyway.I believe the argument for why having lower ratings for fuses is unacceptable has to do with something in the regs about "all inputs". The basic idea is that the meter must protect you, up to the rated voltage, against the error of putting the leads in the wrong sockets. It happens if you're tired, in a confined space or just unattentive. I've actually done this with an unfused Harbor Freight meter (not the free one) because I had it set up with three leads, one in the 20A socket, for working on automotive electrical systems. It was handy for that, but then when I tested a wall socket behind a bench and grabbed the wrong lead....zzap! So to meet the current requirements for a handheld meter, I believe the fuses must be rated for the highest voltage stated on the front label.Bench meters with CAT ratings apparently do not have to meet the exact same requirements and inputs other than the main voltage sockets are often labeled for a much lower voltage and sometimes there is a lower voltage from common to ground. On a Keysight 34401A, for example, you could measure a ground-referenced 1000VDC if your common was put to the ground but not the other way around.To expand on the interpretations theme, one thing that the anti-cheapie brigade may not be considering is that some of these meters may have actually passed relevant transient testing based on one possible interpretation of the standard. Here are two competing and plausible interpretations just for discussion. I'm not claiming either is totally correct and if I were presented with the entire relevant set of standards I might well have to concede that one or both of them was incorrect. And of course there is a lot more to it, insulation test, clearance/creepage, etc.1. The minimal interpretation: The meter should withstand full rated voltage as listed on the front panel in all selectable ranges without damage, except for the fuses blowing on the current ranges. The meter should withstand the relevant transient testing in all voltage modes without exploding OR perhaps in all modes without exploding, but without a requirement of continuing to work.2. The maximal interpretation: Same as the above except the meter should completely survive the transient testing in the voltage modes and not explode in any mode. I'm not aware of any requirements stating that the meter must take a transient in the ohms mode and remain undamaged. The fact that some do may be a design accomplishment or just a side effect of the protection of other ranges. The modern PTC-first method is pretty effective at this if properly implemented.I don't think we can conclude that a Zotek or Uni-T meter with at least a PTC and few MOVs might not have actually met a lab test based on something like my first interpretation even at CATIII/1000V transient levels. My HF meter took a direct short across a fairly short mains circuit and didn't explode or burn, just blew the traces of the PCB. I even fixed it.However, this isn't really a pro-Zotek argument, it's sort of the other way around. I think a certification (real or not) is easier to come by than a reputation built on decades of research and performance.The other burning question seems to be along the lines of "should we allow these meters to exist" or something like that. I think one problem is that these CAT requirements are sometimes in direct conflict with certain functions of the meter that you'd like to have. I have a bench meter that has a diode check with a selectable range of 5V or 10V along with selectable current. It is rated CAT II/600V, good by bench standards but weak compared to handhelds. The EEVBlog 121GW has a 15V diode check and hasn't done well in thejoeqsmithDMM demolition derby. At least part of the issue is that it is harder to clamp that current source when you go above about 5V where a transistor pair alone won't work anymore. There are many other handy features that would be nice to include on hobby or bench meters and it would be a lot easier (and cheaper) if they only had to meet a much lower standard, such as CATII/300V or perhaps none. Nobody tests a VNA, LCR meter or FET probe by plugging it into a wall socket and an inexpensive but sensitive multifunction bench device probably shouldn't be judged with CAT IV transient test. Unless, of course, they actually print the rating on the front in which case they deserve to be fried.

author: joeqsmith
author_rank: Super Contributor
timestamp: January 26, 2025, 08:54:29 pm
content: Quote from: bdunham7 on January 26, 2025, 08:42:09 pmMost electricians don't carry a bench meter. The safety standards are specific to handhelds. See attached title sheet.Quote from: bdunham7 on January 26, 2025, 08:42:09 pmI have provided snippets from the standards regarding this and have mentioned talking with different manufactures to get their interpretation. I have said that Fluke was one of the companies who stated no damage. At least from my own testing, I suspect the more respected brands in the industry also interpret the standard this way. At least, that seems to be what my data is showing. Sure, I can damage any meter but at that 6kV cutoff, the name brand meters (that are brand new) have survived without any issue.To me this make more sense and any damage suggests something broke down. With a high energy source, it seems like the outcome would be very unpredictable.Quote from: bdunham7 on January 26, 2025, 08:42:09 pmSomeone here posted a link to a video from maybe Brazil. It was some sort of TV sales channel where they try and peddle random products. From what I remember, the lady who was show the products was trying to demonstrate one of the 830 hand held meters. She plugs it into a floor outlet. Looked like the meter was set to Amps. There was some excitement and pause, then lots of laughter.With so much chat here about safety and home use, I am surprised that no one has provided their home's fault currents other than myself. It seems like this is something pretty basic for actual electricians to measure. It would be interesting to know what other parts of the world are like.

author: bdunham7
author_rank: Super Contributor
timestamp: January 26, 2025, 09:02:57 pm
content: Quote from: joeqsmith on January 26, 2025, 08:54:29 pmTrue, but AFAIK there are also safety standards applicable to bench meters and other instruments, no?. One thing I'm getting at is that applying the former standards based only on the device form factor or power source might be an outmoded way of thinking. If the little Zoyi 70x-series scopes or Aldo's beloved ZT-225 were deemed a bench instrument, or perhaps reworked like the Fluke 37, there wouldn't be much controversy over their protection level. Unless they put silly labels on them.

author: joeqsmith
author_rank: Super Contributor
timestamp: January 26, 2025, 09:22:57 pm
content: There are the General Requirements.

author: tooki
author_rank: Super Contributor
timestamp: January 26, 2025, 09:29:30 pm
content: Quote from: Aldo22 on January 26, 2025, 05:52:14 pmOK, fair enough. Your statement was ambiguous but I now see what you meant.Quote from: Aldo22 on January 26, 2025, 05:52:14 pmAs I wrote in my previous reply, they might not meet any CAT rating. With few exceptions, 5x20mm fuses are rated only to 250V (and the labeling on it suggests they understand this), but the CAT rating system explicitly disallows reduced specifications on certain input jacks:https://www.eevblog.com/forum/projects/cat-ratings-and-interpretation/Quote from: Aldo22 on January 26, 2025, 06:54:10 pmIt might be “correct” in the sense of being true, but it also invalidates any CAT rating it claims to have, as the meter only gets the rating of the “weakest” input jacks, since the rated voltages must be applied toallinput jacks to pass testing. (See link above.) You can’t have some jacks CAT rated and others not.Note also that the CAT rating system uses a finite list of categories, working voltages and transient voltages. The working voltages are 150/300/600/1000V, and each combination of working voltage and category must withstand a specific transient voltage which is MUCH higher than the working voltage. (The absolute lowest CAT rating possible is CAT I 150V, and even that requires testing a transient voltage of 800V! CAT III 1000V and CAT IV 600V must both withstand a transient of 8000V (which is why that combination of ratings is super common), and CAT IV 1000V must withstand a 12000V transient!)See the attached table I stole fromhttps://www.sanwa-america.com/blogs/news/multimeter-category-ratings-explainedAnyway, since there are no 250V CAT ratings, they could only submit it as 150V if any part of any input is rated only to 250V.

author: Someone
author_rank: Super Contributor
timestamp: January 26, 2025, 09:45:52 pm
content: Quote from: bdunham7 on January 25, 2025, 04:40:26 pmAh, you care about this so much you dont read the standards but want to discuss them?https://www.eevblog.com/forum/testgear/multimeter-cat-ii-rating-discontinuation/msg4984189/#msg4984189Arc flash is a real hazard in many counties. Just because it is extremely rare in your country with its wimpy mains supply, does not mean that applies worldwide.Subtleties matter here, boldly disclaiming arc flash in any residential install is plainly dangerous and incorrect.

author: tooki
author_rank: Super Contributor
timestamp: January 26, 2025, 09:51:00 pm
content: Quote from: Someone on January 26, 2025, 09:45:52 pmArc flash is not minimized in “120V” countries, since they actually use center-tapped 240V (and 208V three-phase industrially) — and due to the lower voltage, the current is higher, and the wiring thicker, theoretically allowing higher short circuit currents.It is true that an arc flash is unlikely in a residential setting, at least in terms of the home’s main breaker panel (consumer unit). The same may not be true of the utility disconnect, especially in a larger multi-dwelling unit.

author: Someone
author_rank: Super Contributor
timestamp: January 26, 2025, 10:12:17 pm
content: Quote from: joeqsmith on January 26, 2025, 08:54:29 pmThat would be because you insist on only measurement, and not taking the range of fault currents from installation standards.You find some number of "safe"/benign situations and claim it is on us to find examples of more dangerous ones, yet we know there dangerous situations exist as they would fail to meet the local (Australian and UK) electrical codes for installations if they had any lower fault energy.It is safer to take a well supported (by the standards in question) position of assuming every outlet could be Cat II/III (depending on which side you are) unless otherwise proven for that specific situation.

author: bdunham7
author_rank: Super Contributor
timestamp: January 26, 2025, 10:31:29 pm
content: Quote from: joeqsmith on January 26, 2025, 08:54:29 pmQuoteI've guesstimated and sort of measured at various points. I've sort of guesstimated that I have 5000A bolted fault current at my breaker bus bars based on the proximity and size of the transformer and the size of the down cable. I've sort of measured that my worst socket in the garage has about 300A fault current (about as low as the 5% rule would permit) and perhaps 500A on the socket that I blew up with the meter. However, when you are abusing a meter the impedance of the test leads, fuse and shunt all reduce that somewhat. The HF freebie is about 150mR on the 5A range, that's pretty low but it has short and not-so-thin leads, short PCB trace and no fuse. I'm sure that's to insure a low burden voltage.

author: Someone
author_rank: Super Contributor
timestamp: January 26, 2025, 10:32:08 pm
content: Quote from: tooki on January 26, 2025, 09:51:00 pmLook at the examples measured, or the installation standards. Prospective fault current (ONE of the things that distinguishes a CAT II/III meter with its higher breaking capacity fuses) is often quite low in the US compared to other regions.I didn't mention voltage, but there seems to be some significant US blinkers/blinders around electrical safety in the area of current too.

author: bdunham7
author_rank: Super Contributor
timestamp: January 26, 2025, 11:02:50 pm
content: Quote from: Someone on January 26, 2025, 09:45:52 pmWe're not even discussing standards anymore. To be clear, I'm not advocating for non-compliant multimeters but I am advocating only making defensible, true arguements against them not fairy tales about ogres that may or may not exist. And yes, I am US-centric because that is what I know about so if the numbers are different elsewhere lets look at them.QuotePerhaps there are examples somewhere where I am incorrect, but I'm basing that on arc-flash in low-voltage systems being almost if not entirely a 3-phase issue. If you have three-phase residential, which I know does exist, then you're right and I'm possibly incorrect in those instances. Discussions, papers and guidelines elswhere regarding NFPA guidelines for PPE and labeling show that arc-flash below 300VAC is uncommon although they have happened (very rarely) in 240VAC or even 208VAC 3PH panels where very high fault current is available. I'm going to say it one more time with some extra caveats: Arc flash in a residential system with single phase 240VAC and <10kA fault current is unheard of. A big spark and even a bit of molten copper is not arc-flash. If you know of any case where there has been an actual arc-flash incident in a residential power system please tell us.Here is a free online calculator that purports to calculate the energy and PPE level required for various voltages and currents. You can note first that they refer to "3 phase bolted fault current" and there isn't even an option to calculate single-phase. Next, put in some numbers and you'll see that at 240VAC 3PH you have to have more than 9kA fault current to even get into the lowest category of arc-flash PPE.

author: tautech
author_rank: Super Contributor
timestamp: January 26, 2025, 11:07:43 pm
content: Unless arc flash plasma is contained AC interrupts it. HV DC is entirely a different matter.....

author: bdunham7
author_rank: Super Contributor
timestamp: January 26, 2025, 11:10:28 pm
content: Quote from: Someone on January 26, 2025, 10:12:17 pmOK, so here in the US a residential service would normally be limited to no more than 10kA fault current and both main and branch MCBs are rated for 10kA interrupt. How high can it be there? Are all your breakers rated for more than that? Why would a residential installation have to have such high bolted fault current?

author: Someone
author_rank: Super Contributor
timestamp: January 26, 2025, 11:28:18 pm
content: Quote from: bdunham7 on January 26, 2025, 11:10:28 pmThis is the point, which CAT rating(s) map to at least a 10kA breaking capacity?In the installation I just grab a CAT III 300V or higher rating and roll with it (which may not have a clearing capacity of 10kA !@)The "argument" which this explodes into every time starts with glass fused crap meter is fine for mains,sometimestrue but not always. Significant fault energies can exist at consumer mains outlets in abnormal/fault conditions. Which small glass fuses are not able to protect against.

author: Someone
author_rank: Super Contributor
timestamp: January 26, 2025, 11:37:27 pm
content: Quote from: tautech on January 26, 2025, 11:07:43 pmGenerally true for small unconfined arcs, but at higher energies that falls apart. Even "small" fuses end up with similar capacities for AC and DC.

author: bdunham7
author_rank: Super Contributor
timestamp: January 26, 2025, 11:50:53 pm
content: Quote from: Someone on January 26, 2025, 11:28:18 pmI don't think they're fine and I don't intentionally use them, but you're not going to get an arc-flash even if they burst. They're simply isn't enough energy for it, especially after you factor in the test leads. However I have to ask--why are those crappy glass fuses fine for protecting test equipment, household appliances, hi-fi gear and christmas tree lights (talk about small and crappy) but somehow not OK in multimeter? A transient at the right time and place can short those out just as easily as a cheap meter.I also still don't understand why meters designed for electricians even have fuses and amp ranges. Perhaps we should go back to Volt-Ohm meters and ammeters can be separate instruments or perhaps an add-on module. Other than 4-20mA control loops, which can be designed as protected without fusing, I can't imagine an industrial or residential electrician ever disconnecting a wire and running current through the meter.

author: tautech
author_rank: Super Contributor
timestamp: January 26, 2025, 11:50:59 pm
content: Quote from: Someone on January 26, 2025, 11:37:27 pmOne should also mention the fuse type with ceramic being the standard for containing arc plasma....one cannot say the same about glass fuses !

author: Someone
author_rank: Super Contributor
timestamp: January 26, 2025, 11:56:03 pm
content: Quote from: joeqsmith on January 26, 2025, 08:54:29 pmToday there was an opportunity to measure droop with a non trivial resistive load in a small residential property.Socket A: 0.31R line + neutral for approximately 0.765 kASocket B: 0.23R line + neutral for approximately 1.0 kA

author: bdunham7
author_rank: Super Contributor
timestamp: January 27, 2025, 12:02:26 am
content: Quote from: Someone on January 26, 2025, 11:37:27 pmIf you look at the fusing times for something like the DMM-B-11A the clearing time at high currents is much less than a half-cycle of AC so the distinction between AC and DC is less relevant. The fuse you posted will clear in <100µs. Whether the arc would have self-extinguished at the next crossing doesn't matter.

author: Someone
author_rank: Super Contributor
timestamp: January 27, 2025, 12:06:58 am
content: Quote from: bdunham7 on January 26, 2025, 11:50:53 pmSays you. 1kA of fault at the clearance time of a fuse equals dozens to hundreds of joules (or worse if the fuse doesnt break the current). Plenty of energy to create significant mechanical hazards if it is released.Quote from: bdunham7 on January 26, 2025, 11:50:53 pmhandheldmultimeterWe've seen that argument before too:https://www.eevblog.com/forum/testgear/trashy-meters-redux/msg4834631/#msg4834631Distance (generally) matters in these types of situations.

author: Someone
author_rank: Super Contributor
timestamp: January 27, 2025, 12:17:23 am
content: Quote from: bdunham7 on January 27, 2025, 12:02:26 amFFS take the whole quote rather than move it out of context. Those are two separate statements. Separated by the universal separator of a period/full-stop.Can an AC arc sustain its self over multiple cycles? yes.Do some fuses have similar operation for DC and AC? yes.Are these points relevant to safety of multimeters? yes.A fuse whichmay notbreak the arc (DC or AC) is a danger, and these fuses are known to exist in low cost meters. A warning about the risks is valid.That leads to people claiming the source of the danger does not exist as there is never enough current available. Which has been shown to be incorrect by either examination of the electrical "codes", or by measurement (now done by both myself and joeqsmith)Dangerous situations exist at some socket outlets, proven, shown, fact. Some multimeters are not rated to withstand those conditions, proven, shown, fact. Therefore said multimeters should not be used on otherwise unqualified mains sockets or connected equipment. But somehow that logical conclusion produces mayhem on this forum. Despite that being exactly what the standards say!

author: bdunham7
author_rank: Super Contributor
timestamp: January 27, 2025, 12:26:02 am
content: Quote from: Someone on January 27, 2025, 12:06:58 amYes, the piece of crap may well melt your meter and burn down your house but that doesn't make it an arc-flash. This is definitely a place where 240VAC is going to be a lot different than 120VAC, those glass fuses can have interrupt ratings of 10kA at 125VAC but only 35A at 250VAC. Just switching to fast-acting ceramic of the same size makes a huge difference.QuoteActually to answer my own question, decent appliances with the potential for low-imedance faults often use ceramic fuses and the glass versions are more often found in inherently impedance-protected devices like mid-to-small transformers.

author: bdunham7
author_rank: Super Contributor
timestamp: January 27, 2025, 12:38:40 am
content: Quote from: Someone on January 27, 2025, 12:17:23 amIf you're going to demand careful reading of what you say, please do the same for me. I've never made any claims that danger does not exist, I said that there isn't enough energy for arc-flash--that being a very specifically defined phenomenon. I suspect that the actual physical danger from glass-fused multimeters is probably lower than is commonly imagined here, but I didn't say it was zero or that I approved of such junk.

author: Someone
author_rank: Super Contributor
timestamp: January 27, 2025, 12:51:43 am
content: Quote from: bdunham7 on January 27, 2025, 12:26:02 amSo you discount the possibility of any arc event based on what? The energy is available, the conditions of high current through a small gap can produce an arc. But you just claim it will never be a problem with no justification. It may not be the spectacular room encompassing arc flash that a higher energy fault could cause, but a smaller transient arc "flash" in close proximity to a human is still a significant hazard.Even your claims about fuses are faulty as they are some nonspecific imagined/suggested characteristic and not some guarantee of minimum performance. Referring to a concrete example (well regarded brand name) ceramic fuse data sheet below even with its higher breaking capacity than your example, that could still fail to break the prospective fault current present in the residential installation I just measured. A "good" M205 fuse in a typical (Australian standard electrical install) situation is still failing to guarantee safety.What's the title of xx61010 ?"Safety requirements for electrical equipment for measurement, control and laboratory use"A standard to provide some high level of certainty ofsafety. Which your example is on the side of being unable to provide any significant level of guarantee or certainty.So again you're failing on the basics. Does the fuse meet the accepted standard for minimum guaranteed performance? No. Therefore by the standard it is considered unsafe.

author: Someone
author_rank: Super Contributor
timestamp: January 27, 2025, 12:57:14 am
content: Quote from: bdunham7 on January 27, 2025, 12:38:40 amSo if there is not enough energy for an arc flash, what is that claim based on?How much energy is needed for an arc flash?Is there a voltage or current minimum threshold?Having worked in the practical uses of electrical breakdown (ie. arcs and plasma) I dont believe there is any practical limitation preventing mains supplies from arcing in a dangerous way (to someone in close proximity as they may be when using a handheld multimeter).I never said you claimed there was not enough fault current. But that is basically the same as you saying (without any further detail) that there isn't enough energy to be dangerous.Can I throw a few dozen joules at your eye? or perhaps a few hundred joules at your reproductive organs?

author: bdunham7
author_rank: Super Contributor
timestamp: January 27, 2025, 01:24:05 am
content: Quote from: Someone on January 27, 2025, 12:57:14 amThe definition of the arc-flash hazard that requires protection is that which exposes the user to more than 1.2cal/cm2of radiated energy. The arc-flash typically occurs when there is enough plasma to short out the three phases resulting in a rapidly expanding ball of plasma, literally an explosion. The process typically starts in 3PH systems with more than 300V phase-to-phase but can start in 240 or even 208VAC systems. The voltage and current needed to cause a particular level of hazard depends on the exact configuration of the electrical box, the spacing of the conductors, etc. I've linked an online calculator that you can put in all the various parameters and select the model and get the exposure level. If it is over 1.2cal/cm2then you have an arc-flash hazard.The three-phase requirement is obviously not an absolute one, but single phase AC systems would have to have much, much more energy to sustain an arc or cause the arc-flash event within a half-cycle. That's a problem for medium and high voltage distribution systems. There's a separate section, requirements and calculator for DC arc-flash.

author: Someone
author_rank: Super Contributor
timestamp: January 27, 2025, 01:38:10 am
content: Quote from: bdunham7 on January 27, 2025, 01:24:05 amSo it only took you 2 pages to actually define your narrow definition of "true" arc flash, and still no evidence of how that is impossible with typical consumer outlets. General guidance from wikipedia is not safety standards.Real world people avoid electrical hazards from uncontained arcs:or graphic content warning:I'm not going anywhere near those situations with a meter that cant reliably break the expected fault current, same on the consumer side of the socket.

author: bdunham7
author_rank: Super Contributor
timestamp: January 27, 2025, 01:58:05 am
content: Quote from: Someone on January 27, 2025, 01:38:10 amIt isn't my definition and I didn't get it (or anything) from Wikipedia. It's an industry standard--don't you support those? The evidence is the calculator. There are many other professional, technical sources for this same information.QuoteThe first video is quite silly and certainly isn't an arc flash. The second is a long story about an electrical burn of some sort. IDK if you could get to the arc-flash threshold by shorting out the bus bars with your hand a half-inch (or whatever) away, but if it can be done on a 240V panel that would be what it would take. A sustained arc below the threshold would cause some damage as well. He doesn't say whether the arc just went out on its own or if it was interrupted by the utility transformer fusing.I support your decision to not directly short out your naked bus bars with a cheap fuse.

author: joeqsmith
author_rank: Super Contributor
timestamp: January 27, 2025, 02:13:50 am
content: Quote from: Someone on January 27, 2025, 01:38:10 amThanks for taking the time to make a few measurements. Was that at 220V?First video was pretty lame. I get more sparks when welding. Second video was impressive but working right at the feed where he not only has a much lower impedance but also both phases. This isn't the typical outlet in the USA but still a good data point.

author: Someone
author_rank: Super Contributor
timestamp: January 27, 2025, 02:21:45 am
content: Quote from: bdunham7 on January 27, 2025, 01:58:05 amYou've picked one definition for an arc flash which has: "50% chance of receiving a second degree burn"I'd rather not take a 50% risk of a second degree burn thanks.At no point did you try to suggest you were restricting the term "arc flash" to some arbitrary threshold.Quote from: bdunham7 on January 27, 2025, 01:58:05 amAccording to you it doesnt count, but the author calls it an arc flash and I call it an arc flash. So you're on your own there. You'd really be comfortable taking that sort of energetic event to your hand or face?Back to my question, a couple of dozen Joules to your eye? that's the sort of energy we're talking about here.Real dangers, even at 110V outlets.

author: Someone
author_rank: Super Contributor
timestamp: January 27, 2025, 02:23:38 am
content: Quote from: joeqsmith on January 27, 2025, 02:13:50 amWe're 230V nominal, but 240V as installed. Measured 238V.

author: BradC
author_rank: Super Contributor
timestamp: January 27, 2025, 02:29:42 am
content: When I finished my (small wires and volts) apprenticeship I used to work for an electrical contractor. I recall one of the real sparkys being admitted to hospital for "arc flash". He had all the requisite PPE on, but suffered severe UV burn to his face, and was peeing blood for a couple of days. He spent the best part of a week in hospital "under observation".I believe he slipped and shorted a pair of 415V bus bars with the head of his pliers.The only other "arc flash" event I was involved in the investigation of was about 9KV and that resulted in the death of the recipient.Neither of these would be possible on a residential board. Even my 3 phase 415V has fault current relatively limited by the supply side. Yeah, things would go *pop* and there's potential damage to both equipment and operator, but let's be realistic.

author: bdunham7
author_rank: Super Contributor
timestamp: January 27, 2025, 03:33:33 am
content: Quote from: Someone on January 27, 2025, 02:21:45 amNo, I'm really not. Arc flash hazards have been and are widely discussed. The energy threshold is for PPE-level requirements. The concept of how an arc flash starts and how it relates to fuses is complex and I think a bit different than what is commonly imagined. I don't think most arc-flash incidents involve meters, but some do. The main issue with fuses isn't that the meter itself is going to blow up (although they can if you try) or that the arc flash even happens in the meter, it is that the fuses need to open the circuit before the arc and plasma ball grow large enough to short out the other phases. That arc and plasma ball aren't typically happening at the fuse, they're starting at the probe tips. If the fusing doesn't happen quickly enough then once the plasma reaches the other phases the arc flash will continue to grow unchecked until an upstream breaker trips or the whole mess melts down. This type of arc flash, which is what the industry is concerned about and where the vast majority of serious injuries occur, just doesn't happen on single-phase low-voltage systems. That was and is my point. If you want to call a few sparks arc flash, then go ahead. It's not like I invented the concept.As far as fuses go, small glass fuses are atrocious but they probably work sufficiently in the vast majority of cases. For single-phase mains 240VAC or below, a ceramic version with a 1.5kA interrupt rating is likely more than adequate, especially if you avoid the bus bars. Another member has sent me some Aliexpress ceramic fuses to test, maybe I'll add an almost-bus-bar test.One final thought on fuses--if you think the threshold for danger from arc flash is lower than I've stated or that cheap fuses pose a significant threat to your safety when working on residential systems, then you'll need to do a lot more than upgrade your DMM. Most--probably the vast majority--of these accidents are caused by something other than a meter or test probes. You'll need appropriate PPE to mitigate the hazards and a good set of insulated tools to start with.

author: Someone
author_rank: Super Contributor
timestamp: January 27, 2025, 04:14:31 am
content: Quote from: bdunham7 on January 27, 2025, 03:33:33 amEnergy levels which could occur where the user is holding the meter. We know the fault currents and approximate durations. They are in the region of possible injury.Quote from: bdunham7 on January 27, 2025, 03:33:33 amWhy not in the meter? A fuse that doesnt clear the fault current (as has been explained over and over) could result in an arc in/at the handheld meter.Which is why the "serious" meters use HRC style fuses that will open within a defined energy, and typically include mechanical blast protection (not exposed fuses or flimsy fuse doors).Quote from: bdunham7 on January 27, 2025, 03:33:33 amxx61010 standard disagrees, which is the standard for handheld multimeters and is the defining document of Measurement Categories. You can claim you know better all you like but that is unlikely to hold up when the shit hits the fan and you're suddenly liable for damages.You can talk all day long about massive energy arc flashes that meet your idea of what a "true" arc flash is. On the other side we know the amount of energy which can be realistically delivered in the handheld package and they can cause injury, even if the injury isn't meeting your arbitrary threshold you need to simply say that up front. "I'd do this and even if things went wrong there is only a 50% chance of serious burns" vs what I'd push instead of "be safe, even if things go wrong you shouldn't end up injured at all". I stick with the published standards to protect my liabilities and they make sense when you go out and measure the real world (you've magically avoided putting any figures on your claims of insufficient energy).

author: bdunham7
author_rank: Super Contributor
timestamp: January 27, 2025, 05:13:06 am
content: If anyone has any further interest, here's an actual recent doctoral dissertation on this exact topic...https://trace.tennessee.edu/cgi/viewcontent.cgi?article=7349&context=utk_graddiss

author: Aldo22
author_rank: Super Contributor
timestamp: January 27, 2025, 09:41:58 am
content: Quote from: tooki on January 26, 2025, 09:29:30 pmThanks for the explanation!I now understand why it doesn't meet the CAT specification, evenifthe V input aloneshouldmeet the advertised rating.All I can say is that Zotek is apparently aware of the problem, so it comes with “sealed” A inputs. (kidding)In practice, this has no effect on me personally, since- I rarely have to deal directly with voltages above 30V or high energy.- If I have to do something in the CAT II range, I don't use the ZT-225 but the clamp meter (without A inputs, only V and clamp, NCV, live wire, auto function, auto range) or the current consumption meter.I already did it this way when I didn't know much about CAT ratings.Thanks.

author: Fungus
author_rank: Super Contributor
timestamp: January 27, 2025, 02:16:08 pm
content: Quote from: Aldo22 on January 27, 2025, 09:41:58 amMost Chinese meters come with those stickers these days.I think it reflects more on the buyers than on the meters. The sellers are probably sick of getting returns from lesser-informed customers.

author: Aldo22
author_rank: Super Contributor
timestamp: January 27, 2025, 03:29:33 pm
content: Quote from: Fungus on January 27, 2025, 02:16:08 pmThat could be.By the way, if you want to protect yourself from your own stupidity, you can simply plug the A inputs.Sounds too simple? Maybe it will save some fuses if you know that you don't need the current measurement.

author: themadhippy
author_rank: Super Contributor
timestamp: January 27, 2025, 04:26:39 pm
content: QuoteStill wont stop you trying to measure the resistance of the power grid

author: Aldo22
author_rank: Super Contributor
timestamp: January 27, 2025, 04:33:09 pm
content: Quote from: themadhippy on January 27, 2025, 04:26:39 pmThere is some protection for this, at least in the CAT II range.https://youtu.be/UIml3TYDomE?t=316I haven't tried it myself.

author: joeqsmith
author_rank: Super Contributor
timestamp: January 28, 2025, 01:42:14 am
content: Quote from: tautech on January 25, 2025, 08:40:03 pmI've been blasted before about not divulging details about modifications I have made to some of the cheap meters for experimental use. My stance on this has always been that I don't want to provide uneducated individuals something they can just copy paste and become injured in the process. I still take that hard stance today and believe it is negligent and reckless to do otherwise.For example:https://www.eevblog.com/forum/testgear/brymen-bm789/msg3695878/#msg3695878How you feel about that?

author: tautech
author_rank: Super Contributor
timestamp: January 28, 2025, 02:26:03 am
content: Quote from: joeqsmith on January 28, 2025, 01:42:14 am100% supportive and long time follower of your DMM tests and travels......I might remind you of this post:https://www.eevblog.com/forum/testgear/hear-kitty-kitty-kitty-nope-not-that-kind-of-cat/msg826562/#msg826562

author: tggzzz
author_rank: Super Contributor
timestamp: January 28, 2025, 10:36:42 am
content: Quote from: joeqsmith on January 28, 2025, 01:42:14 amVery sensible, IMNSHO.I extend that principle to telling people that some practices/setups/situations are inherently dangerous, but explicitly not advising on how to make them safe. Even if I managed to give good advice about how to avoid the danger in one way, an inexperienced person might think they are safe and get bitten adifferentway. Fools are, after all, ingenious.

author: 2N3055
author_rank: Super Contributor
timestamp: January 28, 2025, 03:37:18 pm
content: Quote from: Aldo22 on January 26, 2025, 09:26:59 am1.3 deaths in a year because of electric work in Switzerland?You are right, that is low number.But, wait, Switzerland? That is, like, most regulated and technical standards strict country in Europe?As they say "running smooth as a Swiss watch..".Country that is epitome of rules dictating every activity...1,3 deaths per year in Switzerland is EXACTLY because VERY strict rules are being obeyed to the letter....In working procedures, equipment used etc...Your data is EXACTLY the proof against your claims. It is a proof that sticking to the rules saves lives.Not that it is safe to use unsafe equipment...

author: Aldo22
author_rank: Super Contributor
timestamp: January 28, 2025, 03:53:09 pm
content: Quote from: 2N3055 on January 28, 2025, 03:37:18 pmYes, of course. Nobody says you should use unsafe equipment.I just wanted to put the problem of "lethal meters", which is discussed up and down here, into perspective.If you're honest, it's not really an issue.But yes, if you warn people, you feel you're on the safe side.It's OK.

author: tooki
author_rank: Super Contributor
timestamp: January 28, 2025, 06:18:27 pm
content: Quote from: Aldo22 on January 28, 2025, 03:53:09 pmNo. If you’re actually honest, then “it’s not really an issue for low-energy electronics”.It certainlyisan issue if we don’t qualify it with any context.

author: Aldo22
author_rank: Super Contributor
timestamp: January 29, 2025, 11:10:49 am
content: @tooki: Look, I know why we're talking past each other.You look at the technical side. You're interested inwhat could happen, i.e. the potential danger, and you're interested in what can be done to make devices safer.That's wonderful and I'm sure you know a lot about it.I, on the other hand, look atwhat's actually happening(or rather: has happened) in our country.You can see that in the statistics.In the latest statistics on electrical work accidents (2014-2023) we see that on average there is exactly 1 death per year.The overall statistics (private and work accidents) don't look much different either.On average between 2014 and 2023 there were 3.1 electrical accidents (per 9 million people) resulting in death per year.For 2017, which pushes the average up ( 8 deaths ), I have details:3 suicides2 accidents with 2 victims each (not further specified).1 accident with a defective electrical device0 accidents at workEvery death is one too many. I just don't know where you got the numbers, that unsafe DMMs pose a worrying risk to the Swiss population.But I'm interested.I'm certainly not in favor of lowering safety standards, but these unsafe DMMs have been around for decades and as far as I can see they don't appear in the statistics.Peace!

author: tggzzz
author_rank: Super Contributor
timestamp: January 29, 2025, 11:30:13 am
content: Quote from: Aldo22 on January 29, 2025, 11:10:49 amThat's a silly figure, about as useful as noting the risk to the Swiss population of death in a glider or scuba or horse riding accident. What is far more useful is the rate for people undertaking those activities.So, what's the accident rate for people using DMMs to measure high energy circuits? (Let's say high energy is mains o higher voltages).Generally the best way of assessing relative personal risk is in terms of micromorts.

author: Aldo22
author_rank: Super Contributor
timestamp: January 29, 2025, 01:08:35 pm
content: Quote from: tggzzz on January 29, 2025, 11:30:13 amMore precise data apparently does not exist, probably because it is statistically irrelevant.In any case, it can't be more than 3.1 on average per year (out of 9 million people, since everyone in Switzerland has electricity at home).This figure alone, which includes all deaths associated with electricity, is statistically negligible (sorry), even though it includes suicides.The data cannot be interpreted further either (no recognizable trend in 10 years, seems random).Comparisons: Switzerland 2017, for example:Alcoholic liver cirrhosis: 421 deaths.Suicides: 1043Don't get me wrong, I don't want to trivialize any dangers, but you have to classify the dangers correctly, at least among adults.If you warn too often for no reason, nobody will listen to you if you warn for good reasons.Warn responsibly!

author: tggzzz
author_rank: Super Contributor
timestamp: January 29, 2025, 01:31:21 pm
content: Quote from: Aldo22 on January 29, 2025, 01:08:35 pmAnd yet you are the one which introduced such statistics into the conversation.QuoteAnd yet you don't classify dangers "correctly".That argument fails when the audience doesn't/can't/refuses to understand the dangers.QuoteOne way of telling whether a statement has any useful content is to invert it. If the new statement is nonsense, then the original statement should be omitted.In that vein... "Warn irresponsibly!"

author: Aldo22
author_rank: Super Contributor
timestamp: January 29, 2025, 02:08:43 pm
content: Quote from: tggzzz on January 29, 2025, 01:31:21 pmIt is up to you to provide this data.You say that unsafe DMMs pose a relevant risk of death for people.I say that I don't believe that and at least I can't find any evidence of it in our country's statistics.So how can you substantiate your claim? Everything else is just opinions.I'm really interested in that, I'm not trying to be offensive.In any case, this discussion was interesting for me because it made me look at the statistics.I was pleased to see that very few people die from electrical accidents in our country.Of course, this is a consequence of safety measures and nobody wants to make it worse.My point is to make a realistic assessment.

author: tggzzz
author_rank: Super Contributor
timestamp: January 29, 2025, 03:12:59 pm
content: Quote from: Aldo22 on January 29, 2025, 02:08:43 pmSigh. You are using statistics in the way a drunkard uses a lamp post: for support rather than illumination.Absence of evidence is not evidence of absence.A fundamental problem with death reports was made extremely apparent during the covid epidemic: differing ways of classifying a death.I expect there is a classification for death by heart attack. Suppose someone is testing something up a ladder, gets an electric shock, falls badly, and has a heart attack. How would that be classified? Shock, fall, or heart attack an hour later. Answer: the medics will see the heart attack and won't know nor care what lead up to it. Guess how the death will be classified.QuoteNo, your point is to make anunrealisticassessment by cherry picking an irrelevant population.The relevant population is the deaths/injuries in the population that uses dangerous DVMs.

author: Aldo22
author_rank: Super Contributor
timestamp: January 29, 2025, 03:20:48 pm
content: @tggzzzThank you.You can insult me as much as you like and talk smart all you want.I'd just like some statistical proof for your assumption. UK statistics are welcome.Can you do that without being contemptuous?

author: tggzzz
author_rank: Super Contributor
timestamp: January 29, 2025, 04:51:14 pm
content: Quote from: Aldo22 on January 29, 2025, 03:20:48 pmPlease indicatepreciselywhere I have insultedyou.Pointing out the flaws in your statements is not insulting you.I note you havestillnot producedusefulstatistics about the proportion of people using DVMs improperly who end up injured. N.B. We don't care about people who never use DVMs.

author: Aldo22
author_rank: Super Contributor
timestamp: January 29, 2025, 05:39:27 pm
content: OK, I conclude that you have no evidence for your assertion.I would have been surprised, because it is difficult to find statistical evidence for largely imaginary problems.You are welcome to provide more information if you have new findings.Thank you.

author: tooki
author_rank: Super Contributor
timestamp: February 02, 2025, 03:13:42 pm
content: Quote from: Aldo22 on January 29, 2025, 11:10:49 amWe know about potential dangersbecause they have happened before.Safety rules are written in blood, as they say.The fact that Switzerland has a small number of electrical deaths isthe result of rigorously applying safety rules, not a reason to abandon them!And it's disingenuous to focus only on deaths. Arc flash injuries can be horrific, if survived. Switzerland may have almost zerodeathsdue to electrical accidents, but the number ofinjuriesis much larger, and some of those will be severe injuries.Either way, I'm also not sure why you're focused on Swiss statistics. This is an international forum where Swiss members make up a tiny minority. Electrical hazards exist worldwide. Heck, if anything, they're likely larger elsewhere, due to lower standards.Quote from: Aldo22 on January 29, 2025, 11:10:49 amI didn't state any numbers. You are the one who keeps bringing up statistics.Quote from: Aldo22 on January 29, 2025, 11:10:49 amAre you really, though? You seem intent on finding any way possible to dismiss safety concerns.Quote from: Aldo22 on January 29, 2025, 11:10:49 amYou say that, but your actual actions kinda say that you believe the standards are excessive, and are based on imaginary dangers.Quote from: Aldo22 on January 29, 2025, 11:10:49 amI very much doubt that anyone in this discussion has done any kind of rigorous statistical research.Publishedstatistics are just overviews and don't typically go into the level of detail that would be relevant here. The fact that they don't call out one particular type of hazard doesn't mean that hazard does not exist or is not significant. Also, not all places collect the data required -- that doesn't mean incidents aren't happening.With that said, some placeshavedone this kind of thing, and have published statistics about multimeter hazards. For example, the province of Ontario. This article covers what the Electrical Safety Authority of Ontario found:https://iaeimagazine.org/2008/july2008/multimeter-accident-prevention-plan-an-electrical-inspectors-survival-guide/Key excerpt from that:QuoteMore on that:https://academic.oup.com/jbcr/article-abstract/31/2/333/4602041See alsohttps://esasafe.com/assets/files/esasafe/pdf/Corporate_Reports/ESA-OESR-2023-AppendixA.pdffor examples of actual incidents involving multimeters.Here's a recent-ish report on low-end multimeter safety from Germany:https://www.bgetem.de/arbeitssicherheit-gesundheitsschutz/pruefen-zertifizieren/pruef-und-zertifizierungsstelle-elektrotechnik/kalibrierung-bericht-schwerpunktaktion-handmultimeterI am not surprised that multimeter incidents appear to be becoming rarer around the world: since the CAT ratings were introduced, and more and more countries have mandated their use for professionals, it makes sense that awareness of them, and the hazards they protect against, has gone up, as has the actual use of rated meters. Again, this is theresultof safety rules, not a reason to weaken them.None of this changes the fact that I actually agree with you that for most electronics use, CAT I rated meters would be absolutely adequate. But those are practically nonexistent, since reputable manufacturers don't bother making such things, and disreputable manufacturers make meters thatmaybemeet CAT I ratings, but lie and advertise higher CAT ratings that they definitely do not meet.

author: tggzzz
author_rank: Super Contributor
timestamp: February 02, 2025, 04:04:35 pm
content: Quote from: tooki on February 02, 2025, 03:13:42 pmThose are all valid points. I'vehighlightedsome that I think will be "problematic" for Aldo22's contentions.

author: Aldo22
author_rank: Super Contributor
timestamp: February 02, 2025, 04:43:07 pm
content: Look, sometimes when you read this forum, you get the impression that DMMs are a leading cause of death, just behind heart attacks.Lowering the panic level does not mean lowering safety standards.But the data we have says that deaths related to electricity in general (at least in our country) are not really an issue, your bold letters don't change that fact.I realize it's written into your electrician DNA to warn people about deadly electricity.That's OK.We could go on and on.I think everyone has made their position clear.

author: tooki
author_rank: Super Contributor
timestamp: February 02, 2025, 05:07:15 pm
content: I’m not an electrician (nor is almost anyone here). I’m an electronics technician.“Not really an issue” is a ridiculous thing to say. Low injury rates are something to be celebrated, not used to justify lowering our standards.Nobody here has ever claimed that multimeter injury is common. Just that it is a real hazard in some circumstances, and that absent an unambiguous statement from the person that they only need it for CAT I-type uses, we err on the side of caution when making meter recommendations.

author: m k
author_rank: Super Contributor
timestamp: February 02, 2025, 05:24:06 pm
content: Impression is personal.Back in the day one farmer died an unnecessary death by electrocution.He had an extension cord with 0-class socket screwed on a stump of wooden board.Without regular rubber boot he also had other non insulating shoes.He was also drilling with wall plugged machine in a barn and standing on a concrete floor.The machine was self repaired and holding screw of plastic handle was through an insulation of live wire inside the machine.

author: tggzzz
author_rank: Super Contributor
timestamp: February 02, 2025, 08:24:54 pm
content: Quote from: Aldo22 on February 02, 2025, 04:43:07 pmThose are strawman arguments that do not address the points many people (including tooki) have made above.Your assertion about a supposed "panic level" is a good indication (a) of the poor quality of your debating style (b) what worries people about your attitude to the subject and (c) how naive beginners might act based on what you have written.Aside, to help us understand your perspective...How many people have known that were killed in accidents?How many people have you watched die in accidents?

author: Someone
author_rank: Super Contributor
timestamp: February 02, 2025, 08:59:32 pm
content: Quote from: Aldo22 on February 02, 2025, 04:43:07 pmBut these threads are continuously filled with uninformed people claiming there is no danger and suggesting the standards are overly cautious and should not be applied. That is literally suggesting a lowering of safety standards.

author: Zero999
author_rank: Super Contributor
timestamp: February 03, 2025, 05:25:29 pm
content: Quote from: Aldo22 on January 29, 2025, 03:20:48 pmAlthough many here appear to be harsh, when it comes to safety, it's necessary. It's better to upset someone, than them harming themselves or others. No one died of hurt feelings.

author: Aldo22
author_rank: Super Contributor
timestamp: February 03, 2025, 05:57:48 pm
content: Quote from: Zero999 on February 03, 2025, 05:25:29 pmI'm pretty sure that more people have died from hurt feelings than from multimeters.But do you really not realize that we are not talking about the same thing?You're talking about potential dangers.You have learned to warn people about the dangers of electricity.This has become second nature to you and that's good.I don't want to argue about it, I don't want to claim anything or be right.I am interested in facts/statistics/accident figures.I want to get a realistic picture of the risk.What's so wrong with that?

author: tggzzz
author_rank: Super Contributor
timestamp: February 03, 2025, 06:07:36 pm
content: Quote from: Aldo22 on February 03, 2025, 05:57:48 pm(snipped questionable points)To help us understand your perspective...How many people have known that were killed in accidents?How many people have you watched die in accidents?

author: Aldo22
author_rank: Super Contributor
timestamp: February 03, 2025, 06:14:40 pm
content: Quote from: tggzzz on February 03, 2025, 06:07:36 pmI have no “perspective”.I don't want to lecture anyone.I'm trying to find out how dangerous multimeters are in reality.Can't we be nice and friendly?

author: m k
author_rank: Super Contributor
timestamp: February 03, 2025, 06:45:02 pm
content: Before or after an accident?For bystander or victim?

author: tggzzz
author_rank: Super Contributor
timestamp: February 03, 2025, 06:46:12 pm
content: Quote from: Aldo22 on February 03, 2025, 06:14:40 pmOf course you have a perspective. Everybody does; it is part of being a human.You are lecturing people.So now youareinterested in statistics; make up your mind. The statistics you want won't be available, for reasons that have been outlined by several people. The statistics you want would obscure the important messages, e.g. avoidable accidents and that safety codes and standards are written in blood.Yes, we can be and are being "friendly". I appreciate it can be difficult to accurately express a view in a native language, doubly so in a foreign language.Should we assume that your answer to the two questions is "zero"? That would help us understand your position. How many people have known that were killed in accidents? How many people have you watched die in accidents?

author: Aldo22
author_rank: Super Contributor
timestamp: February 03, 2025, 06:56:19 pm
content: Quote from: tggzzz on February 03, 2025, 06:46:12 pmOK, Thank you.

author: bdunham7
author_rank: Super Contributor
timestamp: February 03, 2025, 07:01:36 pm
content: Quote from: Aldo22 on February 03, 2025, 06:14:40 pmI thnk the answer is that the likeliehood of you suffering a serious injury using the multimeter in a household environment solely or primarily due to the meter not meeting its stated rating or due to some other defect is very low. "Household environment" means in your house or perhaps outside it if you have external plugs or lights. It does not mean climbing your utility pole or stripping out your service panel or the meter. "Serious injury" means something that leaves long lasting damage, scars, disability or requires significant medical treatment. If you use different definitions for those terms you may come to a different conclusion. A sudden "pop" noise causing you to fall of a ladder or down the stairs doesn't count IMO.My "perspective" is that I generally don't like cheap, fraudulent merchandise. If I were in an appropriate position of authority I would ban these instruments from being imported unless they demonstrated full compliance with the applicable standard. I also think it is not helpful to give people the impression that DMMs should only cost $20 as that may lead to them not wanting to spend $100 on a decent one even though they can afford it simply because they don't think they should cost that much--sort of like eggs "should" cost $3/doz instead of the $9/doz they're going for currently here. I'm just not willing to fabricate or exaggerate the risks in furtherance of those goals.