CAT ratings and interpretation - Page 1
Forum section: electronics / projects

author: Lightages
author_rank: Unknown
timestamp: October 26, 2012, 03:22:07 am
content: I have started this to discuss CAT ratings as there seems to be confusion as to what they actually mean in relation to multimeter design and protection. I am getting confused where in the past it seemed clear to me. I have been believing that a multimeter must meet its CAT specs on ALL functions and inputs. Others here have been stating that the CAT ratings only apply to the non-current terminals.After searching through the maze of trying to get clear results searching online I finally came across this quote from the Gossen webpage and I now remember reading something similar quoted here before."Above all one specific point (chapter 16.2) must be observed in the EN61010-1 standard:“Multimeters and similar devices may not be the source of any danger whatsoever, regardless of the utilized combination of specified input voltages, function settings and range selections. The term danger includes electrical shock, fire, sparking and explosion.Conformity is substantiated by means of the following test:The highest specified, rated voltage for any of the device's functions is applied to each pair of terminals, one after the other, in every possible function and range combination. ...No danger may occur either during or after the test.”Thus every range must now be protected in accordance with the specified measuring category and input voltage (e.g. 600 V CAT IV).This was not required in the past. It was permissible to reduce the overvoltage strength of individual measuring functions (e.g. resistance measurement)."Thus from Gossen's interpretation of the rules it would appear that my assumption was correct.

author: EEVblog
author_rank: Unknown
timestamp: October 26, 2012, 06:07:29 am
content: I recall (I think) Fluke telling me that unlike many multimeter manufacturers, they send their meters for external independent CAT IEC/EN certification rating. They don't simply rely on in-house testing, or worse, in-house verification based simply on design.Dave.

author: EEVblog
author_rank: Unknown
timestamp: October 26, 2012, 06:10:53 am
content: It seems there is a new requirement coming in 2013:http://www.tuv.com/news/en/greater_china/about_us_cn/regulations_standard_updates/latest_regulations_en/latest_regulation_content_en_102086.jsp/Standard%20update%20of%20EN%2061010-1:2001Dave.

author: Lightages
author_rank: Unknown
timestamp: October 26, 2012, 06:14:12 am
content: Any respectable manufacturer would at least send out a sample of a prototype and then later a sample of the first production run to verify compliance, and then anytime after any changes were made in components or design.But my question really is does compliance to the EN61010-1 standard require that all terminals (inputs) comply for the whole meter to comply to the CAT rating stated on the meter as asserted by Gossen on their webpage?

author: EEVblog
author_rank: Unknown
timestamp: October 26, 2012, 06:20:35 am
content: Quote from: Lightages on October 26, 2012, 06:14:12 amNo idea, the full standards document is expensive, and I have yet to find a copy online.Dave.

author: Lightages
author_rank: Unknown
timestamp: October 26, 2012, 06:29:20 am
content: OK, then hopefully someone who has access to the documents can chip in here. I have based my opinions on certain equipment based on the interpretation that equipment must meet its CAT rating on ALL functions and ALL terminals.

author: Wytnucls
author_rank: Super Contributor
timestamp: October 26, 2012, 06:55:16 am
content: As I explained to you in the other thread, connecting your meter in series in a circuit to measure amps, results in very low voltages across the shunt (Ohm's law). So, connecting the meter to 600V or 1000V in series is no big deal, as long as the impedance in the circuit is much higher than the internal impedance of the shunt and fuse, usually about 0.01 Ohm each. Of course, the amps must remain below the breaker's rating (10A usually), or it will blow.Now, if you put a transient of 8000V with an impedance of 2 Ohms on the A or mA range, all bets are off! It is in essence a short! 8000V and 40-50 amps across the fuse would cause havok on any meter. Very few meters will survive that, depending on the transient time.The fuse may not even have time to blow, depending on the rise time, frying the traces upstream.On the mA/uA range, the rectifier bridge and Zener diode would have to take the brunt of it, until the fuse blows.I haven't seen the actual required procedure to test meters. I suspect that all that is required on the amp range, is to verify that in series in a circuit with a 600/1000V power supply with high impedance, there is not leakage or shorts in the meter. I don't see the point of blowing the fuses with anything above 10A/1A on the Amps ranges.So, in essence, most meters are fine with 600/1000V on the amps range and are not limited at all by the voltage rating of the fuses, which is just an indication of their ability to contain the arc and energy, when a short occurs.

author: Lightages
author_rank: Unknown
timestamp: October 26, 2012, 07:12:59 am
content: Your suspicions, and my understanding of what is the actual case, is what this thread is about. I have cited a specific manufacturer which is regarded by many as being one of the best manufacturers in this field. They have made the assertion and have quoted directly from the documents relating to the safety requirements mandated. They have access to the documents and would have great problems if they outright lied about what is required.Feelings and suspicions are a mute point.I hope to put to bed the speculation everyone has about these specifications.Until proven otherwise by the actual full documents or an assertion by a participant in these specifications, I can only fall back on the reputation of Gossen for what has been asserted by them. To whit, and I paraphrase: All equipment that claims to be rated and complies to the standards stated in EN61010-1 must meet these requirements on all terminals (inputs or outputs) for all functions.If this is the truth, then many meters I have seen, seen in tear downs, seen in reviews, and have seen in advertising, are not meeting these requirements and are lies or at best marketing spin that has no basis in the truth in the final product.

author: Wytnucls
author_rank: Super Contributor
timestamp: October 26, 2012, 07:32:41 am
content: Gossen didn't say that a high voltage transient with low impedance has to be applied to the the amps range.Gossen meters might not survive that either! All the documents I have seen so far, only mention high transients on the other ranges.But the crux of the matter is that you thought the low voltage rating of the fuse (250V), meant that the meter didn't meet its CAT rating and that is not the case at all.

author: Wytnucls
author_rank: Super Contributor
timestamp: October 26, 2012, 07:41:58 am
content: The highest specified, rated voltage for any of the device's functions is applied to each pair of terminals, one after the other, in every possible function and range combination. ...No danger may occur either during or after the test.”1000/600V on the amps range is no big deal with most meters. That's probably the easiest CAT rating test of them all.No high voltage transients here...

author: Lightages
author_rank: Unknown
timestamp: October 26, 2012, 07:48:03 am
content: Your opinion is not fact without the documents to back it up.Gossen has unequivocally stated "The highest specified, rated voltage foranyof the device's functions is applied toeach pair of terminals, one after the other, in every possible function and range combination. ...No danger may occur either during or after the test." This is directly opposed to your assertion.Please demonstrate by way of another document derived from the EN61010-1 standard, or the EN61010-1 standard itself, or from a statement from an actual official or inspector of the standard that this is not the case. Without this, Gossen is to be believed and anything else is just personal opinion or speculation.

author: Lightages
author_rank: Unknown
timestamp: October 26, 2012, 07:58:31 am
content: Quote from: Wytnucls on October 26, 2012, 07:41:58 amDump a CAT IV 600V 8000V peak impulse transient 2 Ohm source across a 250V glass fuse and you will see quite the nice reactive high voltage high energy blast of energy. There is no doubt that it will result in a dangerous situation. Where does this not involve high voltage? It is in the specification by your own assertion!

author: Wytnucls
author_rank: Super Contributor
timestamp: October 26, 2012, 08:17:46 am
content: I don't dispute the Gossen statement at all.The highest voltages for CAT III/IV ratings are either 600V or 1000V. Easy test for most meters on the amps range.High voltages transients with low impedance on the amps range would fry most meters, regardless of the fuse in place, so that's why I'm pretty sure it is not part of the test, but you're right, we need to see corroborating evidence.Up to now, I can only refer you to Fluke's documents and others , where there is no mention of the amps range at all, while applying high transients.That's still doesn't explain why you thought that my meter couldn't measure amps above 250V and therefore didn't meet its CAT III/IV rating.

author: Lightages
author_rank: Unknown
timestamp: October 26, 2012, 08:41:23 am
content: Quote from: Wytnucls on October 26, 2012, 08:17:46 amI never said that the meter referenced could not measure current above 250V. The problem occurs when there is a fault causing the fuse to blow when connected beyond its rating. It will be dangerous if happens during CAT III/IV conditions. I am sure that no one here would argue that this is not a dangerous condition.I am making the claim that a 250V glass fuse is not safe for breaking a current under a 8000V 2ohm source fault. By definition the fuse is not rated to do this. Please demonstrate that the fuse in your meter exceeds its 250V rating by placing a 8000V pulse from a 2 ohm source. This of course assumes that Gossen is not lying and that all CAT ratings apply to all terminals on the meter. I for one will not question their knowledge on that assertion without a higher authority.If Gossen is correct, that by definition a meter that does not have sufficient protection on all its terminals to meet the CAT rating is not CAT rated correctly, then yes, your meter does not meet its claim of safety.

author: Wytnucls
author_rank: Super Contributor
timestamp: October 26, 2012, 09:12:08 am
content: Your words:'I agree that my UT71E could be a lemon as far as accuracy goes, but it is clear that the current measurements are not made for more than 250V and thus do not meet their CAT ratings'.Where did you get that 250V figure from, if not from the fuse?

author: EEVblog
author_rank: Unknown
timestamp: October 26, 2012, 10:29:14 am
content: Quote from: Wytnucls on October 26, 2012, 08:17:46 amThere can easily be high voltage transients on the amps range, due to inductance in the leads and system under test when the fuse blows open.Think of back-emf when relays coils switch off for example.So it would seem obvious that the current range has to survive those transients, and likely that the standard might simply use the existing voltage transients source standard as per the volts range for the sake of simplicity. The diode protection in this case should be more than adequate, as evidenced by the Fluke meters not having high energy MOV's on the amps measurement input circuit.Dave.

author: Wytnucls
author_rank: Super Contributor
timestamp: October 26, 2012, 12:08:06 pm
content: Yes, I agree, transients can happen while measuring amps, but I'm still sceptical about the testing procedure.For CAT IV, the test transient voltage would consist of a 12,000V pulse with generator internal resistance of 2 Ohms, applied across the shunt and fuse (0.02 Ohms), for approximately 100 uS. Rise time is 1.2uS with a decay to 50% after 50us.If my calculations are correct, using Ohm's law, assuming DC voltage, that would put about 120V and 6000A across the shunt at peak, unless the fuse can open faster. With voltage rising high and arcing after that, I doubt most meters would survive such a test.

author: Wytnucls
author_rank: Super Contributor
timestamp: October 26, 2012, 12:41:21 pm
content: There is also a good chance that the fuse casing would rupture, with random damage in the meter. How would they decide if it meets specifications? Install a new fuse and see if the meter still works? Are the manufacturers allowed several tests?All this testing is done in-house I guess. Perhaps, independent testing should be required.What if the meter passes CAT IV 1000V on the Volts/Ohms range with flying colours, but fails miserably Cat II on the Amps range. Can it be labelled CAT IV on the Ohms range and CAT I on the Amp range?

author: EEVblog
author_rank: Unknown
timestamp: October 26, 2012, 12:55:38 pm
content: Quote from: Wytnucls on October 26, 2012, 12:08:06 pmBingo.The devices may not necessarily be designed to survive these tests. Survival may not be a requirement, but "failing safe" certainly would be.Why do you think meters have 20,000A interrupting current HRC fuses?Dave.

author: EEVblog
author_rank: Unknown
timestamp: October 26, 2012, 01:05:33 pm
content: Notice how the meter in this Gossen video is being tested on the 10A current jack.http://www.gossenmetrawatt.com/english/seiten/cautiondangerousmultimeters.htmAnd some info here:http://www.gossenmetrawatt.com/gmc/resources/marcom/fachartikel/306_tt1_gb_cat_iv_multimeter.pdfWhatever the standard requires for testing the A jack, whether is the same as the voltage jack (for convenience or whatever), or another value entirely, you can bet it's a big energy pulse.Dave.

author: Wytnucls
author_rank: Super Contributor
timestamp: October 26, 2012, 01:38:36 pm
content: Hey, that yellow thing looks just like my meter!That high energy pulse was waaaay too long, Gossen! 100 microseconds, no more, ok?Yes, your meter has 20,000A fuses, not mine, unfortunately.I had read the Gossen publication, but was none the wiser about the actual testing on the Amp range.I have found the right pdf about multimeter testing, but it doesn't download properly.Here is the link if anybody wants to try:http://bbs.dianyuan.com/bbs/u/58/1455811193738104.pdf(Chinese site)I can't believe that the official document is for sale at such a high price! (About USD150.00)

author: Chasm
author_rank: Regular Contributor
timestamp: October 26, 2012, 02:16:39 pm
content: If you apply such test voltages (including transients) to the amps jacks your meter will no longer work.It isnotexpected to work any longer, at the very least the fuse will have blown. Maybe without internal damage to the meter, given the energy content of some tests probably with. The question this test tries to answer is: Does it blow up, or electrocute, the operator too?Its a destructive test, taking the meter way out of its operational specifications. (100x to 1000x the current rating! Followed by a really™ high voltage spike once the fuse tries to blow.)Again, the question ishowdoes it fail, not if it fails.

author: Lightages
author_rank: Unknown
timestamp: October 26, 2012, 02:21:47 pm
content: I was able to download the document and will look through it and report back later.From what I understand, the intent is not to protect the meter, but the user from harm. The meter can be completely non-functional after the test but nothing can occur that might harm the user.Sure during the short period of time the fuse is intact there might be much less than 8000V across the leads, but as soon as that fuse lets go, almost anything goes as far as the voltage. The voltage could even end up higher due to inductance if the conditions are correct.

author: Monkeh
author_rank: Super Contributor
timestamp: October 26, 2012, 02:43:20 pm
content: Quote from: EEVblog on October 26, 2012, 06:20:35 amWill email you a copy shortly.

author: Neilm
author_rank: Super Contributor
timestamp: October 26, 2012, 04:09:24 pm
content: Multimeters are covered by 61010 part 1 (general requirements), I think that part 030 is the part that covers multimeter. I believe that it only calls for basic mis-connections as the rated voltage without the transient - i.e. if it is a 600V CATIV then you connect your current terminals to a low impedance 600V supply.Neil

author: Jeff1946
author_rank: Regular Contributor
timestamp: October 26, 2012, 04:43:37 pm
content: My way of looking at the CAT rating is no matter what you do, the meter is safe to test any system with the rated voltage. For example a CAT 600 rating would mean you could use it safely on say a large motor powered with 440 VAC. So if you touch a probe to 440 and hold the meter and have your feet grounded no shock. Or you forget and leave it on amps and connect to 440 -- you just blow the fuse. I assume that putting 440 would be ok (not burn out some circuit element) for all potential situations such as ohms, diode, capacitance. Not that I would try it with my own meter.

author: T4P
author_rank: Super Contributor
timestamp: October 26, 2012, 05:24:54 pm
content: wytnucls, you're still getting it wrong.You banged on about the UT71E not going to have anything happen to it if you measure amps. Okay.But did you know what happens if you attempt to measure voltage with the leads in amps? BOOM! If it was 600V? Your supposedly very safe glass fuse BLOWS UP! I have seen glass fuses break into two even with a ultra fast trip breaker (Yes, i have one, i paid good money for that, they trip in 10mS)600V IS FLOWING THROUGH THE DAMN FUSE!Okay then, what's the normal procedure of measuring amps? Break up a circuit right? So technically isn't the circuit's FULL voltage flowing through the fuse?Do you know fuses are safely rated for the voltage before they ARC over even after breaking? Did you know a BS1362 style fuse whether glass or ceramic is 32VDC?YES. 32VDC. 250VAC. What happens if you have 100amps at 600V flowing through the fuse? BOOM IT GOES and it shatters violently.What's worse if it doesn't shatter, it will arc over and possibly meltdown your meter and well your hand too if the extremely loud pop doesn't scare you yetBut after that possibly causing a huge fire due to overheated glass from the plasma in the arcYou know why the safety folks are banging on about CAT ratings? This is the REASON. That's why i'm not too sure about anything UNI-T, but i can certainly the both the fuses in the UT61E to HRC fuse and sockets (like monkeh did, props to him) and install MOVs, i'm all set.If CAT ratings were supposed to be with what? 100A breaking current fuses? If It wasn't neccesary fluke wouldn't bother and all meters will jeopardise somebody's life around the globe every second.8000V across 2ohms is 40kA and you should know that.You seem to bang on about not needing HRC fuses, but the truth is, your life depends on it. If you do say "below 50V" What happens if the seemingly not dangerous 32V circuit HAS a potential 500amps flowing through it? BOOM! Glass fuses shatter easily.The breakover voltage for air might be 1kV/inch but you're wrong if you think the fuse will not arc from end to end, WHEN THEY BREAK they are effectively a few mm apart and that is a recipe for ultimate disaster, that's why you need big or really long fusesBig fuse = more distance to separate the bondwires and well more sandLong fuse = They might be held very tight, so if they break they just go off to the other end bu they have less breaking currentMORE CURRENT = FATTER ARC, MORE VOLTAGE = LONGER ARCAlas, not all BS1362 ceramic fuses are safe. Some of them DO not have sand and thus are not 6kA (or so)And some glass fuses are probably good for 20amps breaking current MAXhttps://www.eevblog.com/forum/product-reviews-photos-and-discussion/beware-the-price-of-some-fluke-fuse-replacement/msg114936/#msg114936

author: Lightages
author_rank: Unknown
timestamp: October 26, 2012, 05:28:24 pm
content: The document is password protected so cutting and pasting is not possible.My findings from the document:1. If there is a choice or range of tests that can be performed on a piece of equipment, the worst case test is to be used.2. All multimeters need to have their maximum safe voltage and CAT rating marked at each terminal unless the capacity is generally stated or understood to be less than 50VAC or 120VDC.3. All replaceable fuses must be marked with their voltage and type on the circuit board or holder.4. Handheld equipment must survive a drop from 1m onto a hardwood surface.5. Creepage distance for a coated printed circuit board at 1000VDC is a minimum of 3.2mm with a test voltage of 4000VDCIt appears that the document link provided is not a complete specification for what we are talking about here. But it is clear that unless a multimeter has clearly stated limits on each of its inputs, it is not correctly labelled.Still no definitive answer from the documents directly but from what I have read so far on the Gossen site and the document linked here, all connections on the meter must meet the CAT rating and must be labelled so or the meter does not comply to the standards.

author: Monkeh
author_rank: Super Contributor
timestamp: October 26, 2012, 05:30:02 pm
content: Quote from: T4P on October 26, 2012, 05:24:54 pmNO. NOT 50VDC. And there's no such thing as a glass BS1362 fuse.

author: Lightages
author_rank: Unknown
timestamp: October 26, 2012, 05:34:57 pm
content: Based on my point #2, it appears that even if the UT71E does pass a test for whatever category it may actually be rated at, it is no compliant to the standards because the current measurement terminals do not state any rating, never mind that they are only good to 250V.

author: T4P
author_rank: Super Contributor
timestamp: October 26, 2012, 05:37:44 pm
content: well not glass BS1362, i mean 5x20 glass fuse. Sorry about that, BS1362 means 6x30 ceramic fuse (i think, because 6x30 ceramic fuses turn up when you search in farnell) but the UT71E appears to use 6x30 glass fuses@LightagesAt least UNI-T has been kind to write "250V MAX" on the UT61E, BUT NOT THE 71!

author: Monkeh
author_rank: Super Contributor
timestamp: October 26, 2012, 05:41:12 pm
content: Quote from: T4P on October 26, 2012, 05:37:44 pm6.3x25.4mm. 1"x1/4".QuoteThen it's not a BS1362 fuse.

author: Wytnucls
author_rank: Super Contributor
timestamp: October 26, 2012, 06:07:11 pm
content: Quote from: Lightages on October 26, 2012, 05:34:57 pmIf I follow your reasoning, this one doesn't meet its CAT rating either, because it has the same markings as the 71D.

author: Chasm
author_rank: Regular Contributor
timestamp: October 26, 2012, 06:18:17 pm
content: Accidents happen in the real world which are similar to the test. Lets derail this thread even more.(I think I told this one before, it still applies.)Industrial setting, putting large machinery into operation. The paperwork for the completion certificate calls for measuring the input voltage. No big deal it's 230/400V the same as in most houses outside of 120V country.Just a bit more current in these busbars. (Like in any good horror movie you should now know will happen by now.)So you grab your brand meter (genuine!) from the tool box, switch it to voltage and take a measurement. Then you notice that the test leads are getting warmer and warmer. A quick look at the meter tells you that you are using the Amps jack instead of the Volts one. Oops! Now you make the significant mistake. You flinch back and manage to draw an arc across the busbars. A few milliseconds later vapor state copper begins to impact your body, followed by large parts of the busbars in liquid form a little bit late. You are very lucky and wearing your personal safety equipment so the next stop is emergency room,not the morgue. A few month and operations later (extensive work on hands and face) you can go back to work, the desk work portion of it.So what did happen?The voltage measurement was taken at the hook up point of the machinery. Which happened to be very close to the 20kV substation transformer. When the test leads created the short between two phases the current, for all practical purposes, was only limited by the resistance of the test leads and the internal resistance of the Amps range. A substation transformer is pretty much the definition od a really low impedance source. The current exceeded the rupture capacity of the fuse. Current continued to flow and things started to get warm in a hurry.The meter was an original of Daves favorite brand. In full working condition, no tampering whatsoeve, original fuse, with current safety certificate. One of the older charcoal ones, maybe a 77 I don't know exactly. (The accident happened at the company my father worked for.)As a result of the accident the company trashed all those meters mighty fast and went with Daves 2nd favorite brand instead. The mechanical jack covers would have prevented this accident.

author: T4P
author_rank: Super Contributor
timestamp: October 26, 2012, 06:20:36 pm
content: No. That's different. Always check the manual.UT71E's datasheet has nothing warning you about the very low capacity of the fuses or the 250VAC limit, but the UT61E does warn you, right in front of the meter.So the UT71E is a stockpile of danger brewing, first it doesn't only probably kill you, secondly you might not even know if it will, if you didn't know they used glass fusesAs for the UT61E, you know you are in danger if you didn't check the voltage BUT at least they WARNED you. IT's written 250V MAX so you clearly the UT61E is a "much better" in terms of safety. Elsewhere tooWait, let me paint another scene for ya. Look at those caps in my picture? Those are 35V 10000uF caps. What if you ACCIDENTALLY measure them in amps while in volts?

author: Lightages
author_rank: Unknown
timestamp: October 26, 2012, 06:34:58 pm
content: Quote from: Wytnucls on October 26, 2012, 06:07:11 pmIt is possible, and I may be wrong too as I stated as it was what I could read from a related document. But the document I downloaded that you linked clearly states that ALL terminals must be marked with their rated capacity. On top of that the battery wire in the UT71E passes through a hole in the circuit board in almost direct contact with the input trace, before any input protection. The battery wire has an insulation rating of 600V, a bit short of the 1000V that it might see.Until we have a full document from the 61010 standard it is still guessing.

author: Wytnucls
author_rank: Super Contributor
timestamp: October 26, 2012, 06:45:37 pm
content: Ok, I can agree with you on this one. Dave may have received a copy. Let's wait and see.

author: Lightages
author_rank: Unknown
timestamp: October 26, 2012, 06:51:12 pm
content: It is also possible that multimeter was designed and released before the latest standard made the markings mandatory, or the image you have found is from before that time and that the new ones have the markings required.

author: Wytnucls
author_rank: Super Contributor
timestamp: October 26, 2012, 06:56:46 pm
content: No, all the Flukes are marked about the same, (check their site)The link I posted points to pretty old regulations though, so the new ones could be quite different.

author: Lightages
author_rank: Unknown
timestamp: October 26, 2012, 06:57:22 pm
content: And for all those installing MOVs or other over voltage devices in your meter where there are empty footprints, maybe you should consider the following possibility.It is possible that the original design called for these components but under standards compliance testing the over voltage devices became THE hazard and were left out to avoid having little hand grenades inside the meter. It is possible that the meter passed the compliance tests after the over voltage devices were removed.

author: Neilm
author_rank: Super Contributor
timestamp: October 26, 2012, 06:58:01 pm
content: As I recall 61010, the instrument should be tested between all combinations of compatible leads - so if you can plug the same lead into both amps and volts, you have to do the voltage test on the amps range. I falls under the forseeable misuse component and risk assessments at the back of the main standard. I cannot remember if it is explicitly mentioned in 61010-2-030. It certainly was in the old edition 2 where there was a specific test at the end (section 15.4 from memory) that covered accidental mis-connections.Neil

author: Lightages
author_rank: Unknown
timestamp: October 26, 2012, 07:01:04 pm
content: So from your experience Neil, the Gossen web page is correct?

author: Wytnucls
author_rank: Super Contributor
timestamp: October 26, 2012, 07:04:16 pm
content: Quote from: Neilm on October 26, 2012, 06:58:01 pmThat would tie up, with the Gossen remarks, about applying the highest rating voltage (600V or 1000V) on all input jacks in turn, to make sure no bodily damage can result from misuse.

author: Unknown
author_rank: Unknown
timestamp: October 26, 2012, 07:14:39 pm
content: Quote from: Chasm on October 26, 2012, 06:18:17 pmThis most likely makes it a CAT IV circuit. I think it applies to circuits with less than 15 meters or so of wiring from the substation.Quote from: Chasm on October 26, 2012, 06:18:17 pmWas the meter CAT IV 400V rated? Assuming this event does not predate IEC 1010. If it does, then it's a good example why CAT ratings were introduced.

author: Chasm
author_rank: Regular Contributor
timestamp: October 26, 2012, 08:59:39 pm
content: Quote from: alm on October 26, 2012, 07:14:39 pmNo idea, too long ago and 2nd hand. Chances are that this was before CAT rating.I guess one of the things to take away is that it does not matter if the meter is rendered unusable in some tests. There are real life situations which can take it way beyond the normal operational parameters. The question is if it fails in a safe manner. Here the goal is interrupting the current and only after that containing the blast.

author: Neilm
author_rank: Super Contributor
timestamp: October 26, 2012, 10:16:52 pm
content: Quote from: Wytnucls on October 26, 2012, 07:04:16 pmThe transient test for a CAT rating is done on the live voltage, usually at the top of the sine wave for maximum voltage. If you attach to an ammeter and apply volts the fuse might have already blown before this peak is reached. A good manufacturer might blow the fuse and then apply the transient to check that it is still OK but I don't believe that this is called for. However, I don't usually work with testing multimeters and the like so I won't say that my word would stand in a court of law.NeilNeil

author: EEVblog
author_rank: Unknown
timestamp: October 26, 2012, 10:17:37 pm
content: I now have access to the 61010 standard and various attachments.The most applicable part in this case appears to be:From 61010-2-033:QuoteandQuoteSo it seems that Gossen are correct about the all terminals test thing. But I cannot (yet) find mention of any CAT-like surge test requirement for the AMP range, hence I guess why the Amps jacks are not CAT labelled. But still the testing must be done at the "maximum rated" voltage i.e 600/1000V presumably with a suitable high current capability source.A further table shows a CAT-II source having <10kA short circuit current, with CAT-III <50kA, and CAT-IV >>50kAAs I said before, there is no requirment to survive this, it just has to "fail safe" and present to hazard to the user.Dave.

author: Lightages
author_rank: Unknown
timestamp: October 26, 2012, 10:31:04 pm
content: Thank you Dave.It is then clear, very clear, that multimeters such as the UT71E that have 250v glass fuses on the current ranges do not meet their claimed CAT ratings. It therefore follows that they probably were not even tested for compliance by any 3rd party.I am glad that the standards are as I had thought and that I had not gone crazy.

author: Lightages
author_rank: Unknown
timestamp: October 26, 2012, 10:33:23 pm
content: Dave:Could you post the actual specifications for voltages, pulses, and impedance used for each CAT rating level?

author: EEVblog
author_rank: Unknown
timestamp: October 26, 2012, 11:51:02 pm
content: Quote from: Lightages on October 26, 2012, 10:31:04 pmJust check to see if it's got a third party testing stamp like TUV et.al on the back. If not then it hasn't been independently tested and certified.BTW, there is no legal requirement to do this, you can either test it in-house, or just suspect it passes based on design. Anyone can slap a CAT rating on their meter, as there is no body to legally enforce it.Of course, you need the CAT rating to sell into the EU now, but I believe still no law to say it has to be independently tested.Dave.

author: EEVblog
author_rank: Unknown
timestamp: October 26, 2012, 11:52:08 pm
content: Quote from: Lightages on October 26, 2012, 10:33:23 pmIt does not seem to be available in a simple paragraph or table etc.Dave.

author: EEVblog
author_rank: Unknown
timestamp: October 26, 2012, 11:54:18 pm
content: Quote

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: October 26, 2012, 11:59:29 pm
content: Quote from: Lightages on October 26, 2012, 10:31:04 pmIs it not the combination of fuse type and casing that determines whether or not it meets the rating? A glass fuse in a suitable case could be as safe as a sand-filled one, providing there was no arc-over risk across the fuse (would probably need to be bigger than 20mm!.Just wondering - do the CAT specs define that it must be user-safe, or also not damage the instrument apart from the fuse blowing?

author: EEVblog
author_rank: Unknown
timestamp: October 27, 2012, 12:11:00 am
content: Quote from: mikeselectricstuff on October 26, 2012, 11:59:29 pmIt is broken down into two types of protection (fuse), certified (presumably certain brand/type HRC fuses), and un-certified:QuoteSo yes, I guess in theory you can use any type of fuse or other scheme provided that it meets the interrupting capability.But multimeter are relatively small, and you have to meet clearance and creepage distance as well. So it is very unlikey that any glass fuse could fulfil both requirements in a standard size meter.So as a meter designer it's easier and more beneficial to use an already approved HRC fuse, so the independent test authority does not have to do additional test and inspection of an "uncertified" device.QuoteFor the voltage CAT tests, it seems so.QuoteFor the Amps test, no, there seems to be no requirement, it just has to not cause a hazard.Dave.

author: Lightages
author_rank: Unknown
timestamp: October 27, 2012, 01:07:33 am
content: Quote from: EEVblog on October 27, 2012, 12:11:00 amFrom this alone, it seems that any fuse must be rated for the CAT rating the meter is listed to have, regardless if it is sufficient or not.

author: T4P
author_rank: Super Contributor
timestamp: October 27, 2012, 04:00:29 am
content: Exactly. My point is clear now, the UT71x is a dangerous object waiting to blow up on your face

author: Wytnucls
author_rank: Super Contributor
timestamp: October 27, 2012, 06:50:34 am
content: It seems to me that most multimeters equipped with fuses will fall under 101.3.2, as fuses are certified overcurrent devices and not current limiting devices.The requirements for misuse protection are then as such:1.The fuses have to have a rated voltage of 1000V for meters with that CAT voltage category. (Both A and mA)2.The rated breaking capacity (Amps) must be equal to 1000V divided by the impedance of the circuit, including test leads, up to a max specified in table AA.1 (?)3.Traces and fuses are checked for arcing, by applying twice the rated CAT voltage (2000V) for 1 minute to the jacks, with a ruptured fuse in place.If these are the new regulations, it would be interesting to see what has changed and how that would affect multimeters sold under the old rules.If Dave could post table AA.1, we would have all the standards for fuse requirements.

author: EEVblog
author_rank: Unknown
timestamp: October 27, 2012, 07:23:18 am
content: Quote from: Wytnucls on October 27, 2012, 06:50:34 amI did above.QuoteSo basically, any meter without a HRC fuse is CAT-I only. i.e. not suitable for any mains use at all, which requires CAT-II minimum.with the added note:QuoteDave.

author: Wytnucls
author_rank: Super Contributor
timestamp: October 27, 2012, 07:34:34 am
content: That could be the case, but remember if 1000V divided by the circuit and test lead impedance is less than what is specified in the table (50kA), that can be used instead.It works out to 50kA without the test leads with 0.02 Ohms for the shunt and fuse.So, it does look like HRC fuses are required.I measured my leads and probes resistance at 0.15 Ohms (not sure if the impedance would be very different), so in this case a breaking capacity of 6kA would be enough. Still in HRC territory, I think.

author: EEVblog
author_rank: Unknown
timestamp: October 27, 2012, 08:41:20 am
content: Quote from: Wytnucls on October 27, 2012, 07:34:34 amA typical M205 250V glass fuse (as used in cheap meters) has a breaking capacity in the order of 60A at rated voltage, up to several hundred A at lower voltages.Dave.

author: Wytnucls
author_rank: Super Contributor
timestamp: October 27, 2012, 09:39:13 am
content: The fast blow ones used in some Uni-T meters, like the 71series, have an even lower breaking capacity: 35A!http://docs-europe.electrocomponents.com/webdocs/058a/0900766b8058a7dd.pdfIs there a date on that document, Dave?

author: Lightages
author_rank: Unknown
timestamp: October 27, 2012, 09:46:31 am
content: So after all of this can you agree that the UT71x series do not meet their supposed CAT rating?

author: Wytnucls
author_rank: Super Contributor
timestamp: October 27, 2012, 10:07:45 am
content: Absolutely, and so do not another myriad of multimeters, unless these are brand new regulations.I never said the 71 met its CAT rating by the way, just that I thought it would be unlikely that a big company like Uni-T would disregard these rules, when it wouldn't be that expensive to comply with them. That is why independent testing is so important, but few people worry about approval stamps on the back of the meters.We certainly have learned a lot with that document, especially about the amps ranges, which do not require high voltage spikes testing.The meters are still reasonably safe, if you make sure your leads are in the right positions and you don't connect to potentially low impedance high voltage circuits.Just in case, I will install 30 kA HRC fuses in my meters, including a GDT on the Volts/Ohms range, since we can't trust the CAT rating on the Volts/Ohms ranges either. Not a garantee of safety, but better than nothing.

author: T4P
author_rank: Super Contributor
timestamp: October 27, 2012, 10:18:28 am
content: You do remember the mA fuses in the UT71 is a tight fit right? No HRC fuses are going to fit in there.That's why it's a dangerous meter even after modifying

author: Wytnucls
author_rank: Super Contributor
timestamp: October 27, 2012, 10:23:42 am
content: Quote from: T4P on October 27, 2012, 10:18:28 amIt is a tight fit, but there is space, SIBA makes a small 1000V 500mA 3AG fuse. No sure what the breaking capacity is yet, but that will do, if it is good enough for Amprobe.http://www.testpath.com/Items/Fuse-500mA-1000V-6x32mm-Pkg-of-4-120-328.htmThe breaking capacity is also 50 kA, so it is an HRC fuse.http://www.siba-fuses.us/upload/documents/catalogues/G_section_Miniature_Fuses.pdf

author: Unknown
author_rank: Unknown
timestamp: October 27, 2012, 12:12:45 pm
content: Keep in mind that the maximum short circuit current through the fuse also depends on the impedance of the circuit. Amprobe may have used a higher resistance shunt, for example. Agilent uses HRC fuses with a higher rupture current than Fluke, this may either be to offer better safety or to compensate for some lower impedance / lower power component in the rest of the circuit. Safety requires a systems engineering approach and actual testing, you can't just add random safety components that are used in other instruments and expect to achieve the same level of safety.

author: EEVblog
author_rank: Unknown
timestamp: October 27, 2012, 12:42:58 pm
content: Quote from: Wytnucls on October 27, 2012, 09:39:13 amYes, the latest June 1012 version. 61010-2-033:2012Dave.

author: EEVblog
author_rank: Unknown
timestamp: October 27, 2012, 12:45:24 pm
content: Quote from: Wytnucls on October 27, 2012, 10:07:45 amWhich is the definition of CAT-IDave.

author: Wytnucls
author_rank: Super Contributor
timestamp: October 27, 2012, 12:53:09 pm
content: I hear you, but I'm just replacing 2 fuses and adding a GDT, with a ready footprint on the PCB. No real drama here.I don't claim this will achieve the same safety level as a Fluke, but it will be better than the original.That's all I'm interested in.I seldom work with 250V circuits anyway, so this is mostly a fun soldering exercise, but I will test it as far as I can go.I know already that it can take 250V on the Volts/Ohms input jack, with any range selected (I dont have a pulse of 12,000V available yet).I will test a short on the fuses with 250V (I don't have 2,000V available to check for arcing yet).I'm going to London soon, maybe Electric Mike can help me here...

author: Wytnucls
author_rank: Super Contributor
timestamp: October 27, 2012, 12:57:56 pm
content: Quote from: EEVblog on October 27, 2012, 12:42:58 pmThat's interesting! Do we know what the changes were over the last 4 years for instance?

author: Unknown
author_rank: Unknown
timestamp: October 27, 2012, 01:10:53 pm
content: Quote from: EEVblog on October 26, 2012, 10:17:37 pmI find this test very curious. I would think that the most likely moment for arcing to occur is right when the fuse opens. The inductive kick from breaking the circuit might cause the high voltage transient, which could ionize air in the fuse. Where would the supposedly two times the rated voltage come from after the fuse has opened?

author: robrenz
author_rank: Super Contributor
timestamp: October 27, 2012, 01:30:12 pm
content: Quote from: alm on October 27, 2012, 01:10:53 pmMaybe that is what the "sand" in the HRC fuse accomplishes, possibly hindering ionization after it supressed the arc flash of the element vaporizing?

author: Wytnucls
author_rank: Super Contributor
timestamp: October 27, 2012, 01:35:15 pm
content: The HRC fuse is supposed to smother the initial arc without breaking.I guess, they just want to make sure that there is no residual arcing across the fuse and traces, after the fuse has done its job.

author: Unknown
author_rank: Unknown
timestamp: October 27, 2012, 02:08:09 pm
content: Yes, a HRC fuse is supposed to prevent this and the standard states that they assume the fuse ratings to be correct. But assuming they are not accounting for transients from external sources, the only reason the transient would occur is because the fuse breaks the circuit. Letting everything settle and cool down first and then apply a transient seems like a poor way to test this to me, although ramping up the voltage at the moment the fuse blows might be a tricky test to perform.

author: robrenz
author_rank: Super Contributor
timestamp: October 27, 2012, 02:21:03 pm
content: Isn't it a way to access the quality of the physical and electrical circuitry design independent of the fuse?

author: Monkeh
author_rank: Super Contributor
timestamp: October 27, 2012, 04:17:55 pm
content: Quote from: Wytnucls on October 27, 2012, 12:57:56 pmSo far as I'm aware, there is no previous version of the document. I certainly don't have access to it if it exists.There are, however, two other revisions of 61010-1, 1993 and 2001, current revision is 2010. Will supply to Dave if he wants them.

author: Neilm
author_rank: Super Contributor
timestamp: October 27, 2012, 04:25:20 pm
content: Quote from: EEVblog on October 26, 2012, 11:51:02 pmTo place a meter on the market in the EU require that it meet the various directives. For multi-meters, these are the Low Voltage directive, EMC directive. In order to meet the Low voltage directive the meter would have to meet the appropriate international standard.For the multimeter this is principally IEC61010. It would have to meet all the appropriate parts of 61010, the general requirements, the parts for the measurement circuits and the parts for any accessories that come with it as standard - for example the leads. If the meter came with rechargeable batteries, it would also have to meet IEC62133, assuming that the batteries had a non-acid electrolyte like Ni-mH or Lithium.I do not believe that there is a requirement to put a CAT rating on the meter if it is not rated for connection to the mains.However, most meters are so rated and many do not meet these standards. I found a very cheap meter in a market and I took it to work where we have some facilities to do CAT rating tests. I ended picking bits of the meter out of the blast case for a week.Quote from: Monkeh on October 27, 2012, 04:17:55 pmIEC61010-2-030 was a new standard. The requirements were originally in the main part one of the 2001 version.There are a lot of changes from 61010 :2001, it now covers different versions of insulation as well as requirements for tracking on PCBs which was not covered at all in version 2001.Neil

author: KedasProbe
author_rank: Frequent Contributor
timestamp: October 30, 2012, 08:58:38 am
content: Reply from Brymen, asking for info related to the updated standard and my BM869 DMMNice to see they had the 3rd edition in mind during design. (doesn't mean that it will pass all new test, we will find out later after re-submit)Quote from: Brymen Product Marketing Manageradd-onQuote from: Brymen Product Marketing Manager

author: Wytnucls
author_rank: Super Contributor
timestamp: October 30, 2012, 04:52:51 pm
content: From the Brymen reply, it seems that the high voltage rating requirements for fuses is a new one, with IEC61010-2-030:2010. That would explain the existence of so many meters with 250V fuses. It will be interesting to see how long it takes manufacturers to upgrade their DMM models to comply with the latest standards.

author: Lightages
author_rank: Unknown
timestamp: November 01, 2012, 03:02:41 pm
content: Actually, from the document I have of the IEC 61010-1 standard dated 2004:"5.1.5.2 Measuring circuit TERMINALSUnless a clear indication (see note below) is provided on a measuring instrument that voltageand current measuring circuit TERMINALS are not intended to be connected to voltages to earthabove 50 V a.c. or 120 V d.c., the TERMINALS shall be marked as follows.a) Measuring circuit TERMINALS for measurements within measurement category I (see 6.7.4)shall be marked with the RATED voltage or current as applicable and with symbol 14 of Table1 (see also 5.4.1 f) and g)).b) Measuring circuit TERMINALS for measurements within measurement categories II, III and IV(see 6.7.4) shall be marked with the RATED voltage or current as applicable and the relevantmeasurement category. The measurement category markings shall be “CAT II”, “CAT III” or“CAT IV” as applicable."AND"16.2 Multifunction meters and similar equipmentMultifunction meters and similar equipment shall not cause a HAZARD in any possible combinationof RATED input voltages, and settings of function and range controls. Possible HAZARDS includeelectric shock, fire, arcing and explosion.Conformity is checked by the following test.The maximum RATED voltage specified for any function is applied to each pair of TERMINALS inturn, in every combination of function and range controls. The test source connected to theequipment measuring TERMINALS during this test is limited to 3.6 kVA for measurement category Ior measurement category II. For measurement category III or measurement category IV, the testcircuit has to be capable of delivering 30 kVA.During and after the tests, no HAZARD shall arise.Multifunction meters and similar equipment are to be tested by changing the Function/Range Selector to allpossible settings while connected to the maximum rated source.”NOTE If test probes are provided with the equipment being tested then they are to be used for the test.Compliance is checked by testing to verify no hazard occurs when switching selector settings."So while yes, there is no explicit statement that the fuses must not be rated below the rated voltage of other terminals it is implied. Obviously some or many manufacturers did not interpret the above correctly or used it as a loophole. It is not a given that a 250V fuse could cause harm in a properly contained housing, but if the fuse is not rated to break the current then other hazards would arise very quickly. I would guess this is why the changes to the latest standard to explicitly prohibit fuses not rated for the highest voltage on the equipment. But either way, if the terminal itself is not labelled for the safe voltage use on the equipment it has not met the standards since at least 2004.

author: Wytnucls
author_rank: Super Contributor
timestamp: November 01, 2012, 04:33:15 pm
content: This is how I interpret the old regulations:Assuming the meter passed the destructive 30KVA 1000V test on the A/mA ranges with its 250V fuses and the CAT III/IV tests on the Volt/Ohm ranges, the correct labelling would be CAT IV 600V CAT III 1000V on the Volt/Ohms jacks and 1A/10A MAX, according to fuse ratings, on the A/mA jacks.I don't see the need to mark the amps jacks with a restrictive voltage if the meter passed the test, not to mention the possible confusion for users, which could lead to voltage measurement with the probes in the amps jacks.If the meter didn't pass the 30KVA test on the A/mA ranges, it would lose its CAT rating on the Volt/Ohms range or at least be downgraded.That would make the labelling correct on most meters built before the new regulations came into effect.

author: Lightages
author_rank: Unknown
timestamp: November 01, 2012, 05:12:10 pm
content: I agree with you. The problem is that there is no requirement for actual 3rd party testing. Therefore, any company could label their meter as meeting a specific CAT rating based on the design only. Perhaps the need to force manufacturers to use fuses rated for the CAT rating stated came from some of these "legally" labelled meters failing in real world conditions and/or tests in a dangerous or harmful way. I would make an educated guess that my UT71E would explode if a 30kVA pulse was passed through the current ranges at 600V. There is no way that little glass fuse is going quench the little plasma fireball that would be created.The problem with the word is that if there is a way to interpret something in a way that meets a spec or requirement in a way that benefits the manufacturer in cost, many will choose that over following the intent of the specification, instead they try to get around it. I suspect that is why the standard for fuses was changed.

author: Wytnucls
author_rank: Super Contributor
timestamp: November 01, 2012, 06:01:44 pm
content: The datasheet for those fast glass fuses states a breaking capacity of 35A for the 500mA one and 100A for the 10A fuse, both at 250V. I'd love to see how they do at 1000V!I can't understand why Uni-T went for those weaklings in the 71 series, when cheap ceramic fuses are available in that 205 size and the PCB had a footprint for a 3AG fuse, from the very first board revision. Not HRC, but it would have been a big improvement anyway.Voltcraft sells the 71 series in Germany under their own brand. I wonder if the fuses were upgraded in that one.

author: Wytnucls
author_rank: Super Contributor
timestamp: November 01, 2012, 09:30:02 pm
content: Here is the certificate of conformity (2009) from Conrad for the UT-71 German brother (Voltcraft VC920):For those who don't know Conrad, they have the biggest brick and mortar electronic shop network in Germany, selling equipment all over Europe and Eastern Europe as retailers and also online.The fuses are the same in both versions:Fuse 1 for protecting the mA range:0.5 A 250 V fast-acting 5 x 20 mm (F0.5A 250V)Fuse 2 for protecting the 10A range:10 A 250 V fast-acting 5 x 20 mm (F10A 250V)

author: Lightages
author_rank: Unknown
timestamp: November 01, 2012, 09:41:04 pm
content: Wow, Conrad really stuck their neck out on that one. The UT71E does not have any 3rd party testing as far as I can see and the Voltcraft rebadge is being guaranteed by Conrad only!

author: Wytnucls
author_rank: Super Contributor
timestamp: November 01, 2012, 10:20:46 pm
content: Yes, they sure did, but knowing how the German companies operate, they must have done some testing of their own or put the meters through a German safety audit, as litigation would put the reputation of the company at risk.They also produced their own operating manual for the meters, in several languages.VOLTCRAFT® products are developed in the “Conrad Technology Centre (CTC).They have been selling these UT71 clones since 1995.

author: T4P
author_rank: Super Contributor
timestamp: November 03, 2012, 08:45:30 am
content: Rebadges not clones.They do the independent testing and probably upgraded the fuses, i remember seeing a UT61X from a german company for slightly more with upgraded fuses

author: Lightages
author_rank: Unknown
timestamp: January 15, 2013, 07:29:43 pm
content: Further information from Brymen in relation to a question I sent them on the altitude specification in the manuals:Altitude up to 2 000 m is the normal environmental condition (clause 1.4.1) in IEC61010-1 safety regulation. Altitude above 2 000 m is specified as extended environmental condition (clause 1.4.2), and all CLEARANCES shall be multiplied by an applicable factor. They are:1.14 at 2001 to 3000 m1.29 at 3001 to 4000 m1.48 at 4001 to 5000 mPer altitude <2000 m, BM869 is a CAT IV 1000V design using clearance of 14 mm, which is, in turn, 1.75 times of 8 mm as in the one step lower CAT III 1000V & CAT IV 600V requirements. It is then a CAT III 1000V & CAT IV 600V design up to 5000 m, the highest altitude as specified in the regulation.Best Regards,Gary Wang/BrymenProduct Marketing Manager

author: safetyfirst
author_rank: Newbie
timestamp: October 08, 2013, 06:50:21 am
content: Here is the timing on the new standards (fromhttp://www.ul.com/global/eng/pages/offerings/industries/healthsciences/ul61010/):UL 61010 Part 1 - 2nd edition (published 7/12/04) combined the three previous UL standards into a single standard- UL 61010A-1 for laboratory equipment- UL 61010B-1 for test and measurement equipment- UL 61010C-1 for process control equipment into a single standard.UL 61010-1 2nd edition is completely aligned with the current edition of IEC 61010-1, except for some U.S. national differences. Since the effective date for this standard is January 1, 2014, and all products that only mee the 1st edition must be withdrawn.There are other dates:October 1, 2013 -- EU date of cessation for IEC 61010-1 2nd edition.January 1, 2014 -- UL 61010A-1, UL 61010B-1 and UL 61010C-1 will be withdrawn.June 1, 2014 -- All new product submissions that are in the scope of IEC61010-2-033 must comply with this standard and UL61010-1 3rd editionJanuary 1, 2018 -- UL 61010-1 2nd edition will be withdrawn.We are now in the middle of the transition. All new submitted products must meet the new requirements. Previously approved products can continue (until 2018?). Based on this thread, a safer DMM should meet the 3rd edition requirements

author: Lightages
author_rank: Unknown
timestamp: October 08, 2013, 06:55:10 am
content: Thanks for the update.