Interesting and sad case of electrical injury - Page 1
Forum section: electronics / projects

author: calzap
author_rank: Frequent Contributor
timestamp: May 24, 2024, 06:40:48 pm
content: Encountered this story in recent issue of EC&M magazine. Although similar stories are easy to find on the net, this one caught my eye because of the before and after pictures. At an industrial job location, the foreman of an electrical crew assigned an apprentice to tidy and clean-up some switchgear. He told the apprentice not to work on anything “hot” and walked away. Apprentice was to determine what was hot with a multimeter which was not rated for some of the voltages in the facility. Apprentice was not wearing any PPE. Everything went well until the apprentice opened a cabinet with 4,160 V potential transformers. See first picture. Given the small size of the transformers, I assume they dropped the voltage for sensing and control purposes. There was no high voltage sign on the cabinet. The apprentice dutifully put the meter probes on the primary conductors. The conductors, probes and meter exploded in a ball of fire. See the last two pictures. It’s obvious which two conductors were probed. Can anyone identify the meter? Looks like the plastic shells of the transformers burned or vaporized. Apprentice sustained severe burns and spent several days in a hospital burn unit. Was not stated whether there were permanent injuries.The contractor and facility owner were both to blame, but the bulk of the blame is on the contractor. The foreman knew that some of the cabinets had high voltage. The apprentice should have never been allowed to work on the equipment alone. Anyone working on it should have had appropriately rated equipment and should have been wearing PPE. Unless functional testing of the transformers was needed, power should have been locked-off upstream. Was not stated whether fire-fighting equipment or first aid supplies were present or what penalties were imposed.Mike

author: Gyro
author_rank: Super Contributor
timestamp: May 24, 2024, 07:29:39 pm
content: Quote from: calzap on May 24, 2024, 06:40:48 pmSeveraldays? I would say that he was incredibly lucky! People can spend months in those burns units.That meter does look vaguely familiar from old magazines, amateur grade.

author: Kim Christensen
author_rank: Super Contributor
timestamp: May 24, 2024, 07:52:55 pm
content: The meter looks like this one:

author: Stray Electron
author_rank: Super Contributor
timestamp: May 24, 2024, 08:00:03 pm
content: I think there must be a LOT more to this story than what the article is telling! First. what exactly did they mean by "tidying up"? It already looks pretty clean to me. Also how did they just happen to have a "before" picture? Also any meter should be fused and even if it wasn't, 4,000 volts should have just fried the meter and not caused all of the damage outside of the meter and to the meter leads and inside of the electrical cabinet.I spend a few years working with 12,000 volt systems and later spend 4 years working on U.S.A.F. Search RADARS that operated at 15,000 volts at 200 amps and I've never seen anything like this. 4,000/ 12,000/ 15,000 volts really aren't that dangerous IMO as long as you follow the proper procedures.I did see one high powered 480 3 phase AC electrical cabinet burn up, similar to this, after the cleaning crew sprayed it directly with a VERY high pressure water hose!But IMO the damage in the pictures wasn't caused by someone probing with a meter.

author: Gyro
author_rank: Super Contributor
timestamp: May 24, 2024, 08:09:38 pm
content: Quote from: Kim Christensen on May 24, 2024, 07:52:55 pmYes, that's the one. A 2 socket special with current ranges! 20mm glass fuse at best. Ancient.

author: ejeffrey
author_rank: Super Contributor
timestamp: May 24, 2024, 08:32:34 pm
content: Does that meter have a 20 amp range on the same jack as the volts? That's nuts.

author: thm_w
author_rank: Super Contributor
timestamp: May 24, 2024, 08:34:47 pm
content: Quote from: Stray Electron on May 24, 2024, 08:00:03 pmThe before photo is a different cabinet.

author: Gyro
author_rank: Super Contributor
timestamp: May 24, 2024, 08:48:22 pm
content: Quote from: ejeffrey on May 24, 2024, 08:32:34 pm200mA but it doesn't matter at that point, it's as near a HV short as makes no difference. Yes, absolutely nuts to be in that environment and a fuse eater on an amateur's bench. It was a Radio Shack brand!

author: calzap
author_rank: Frequent Contributor
timestamp: May 24, 2024, 09:10:47 pm
content: Quote from: thm_w on May 24, 2024, 08:34:47 pmYou're right. No wires entering the top of the cabinet in the before photo, but there are in the after photo.

author: coppercone2
author_rank: Super Contributor
timestamp: May 24, 2024, 09:11:34 pm
content: Well I noticed if you probe a high voltage circuit you get sparks on the leads for a meter (i.e. vacuum tube transformer), even a 34401A when you probe it near the limit of the voltage. something is getting chargedI think the problem is cheap meter. I see what the radio shack meter has is like a little bead MOV on the input. It does not have any special box for containing and directing plasma etc. The protection element shorted and blew up the meter. MOV turn into plasma when they get hit hard enough, I saw it happen in a power strip.The better things use protection to help contain the blast, heat shrink, kapton, and its own container. I took a RS dmm apart, it just has a blue little MOV sitting out there in the PCB. they give it a bit of spacing from the other parts, but thats it. Chances are the plastic is cheaper too.I think if you don't contain it, the plasma keeps spreading and the 'load' impedance keeps decreasing. so even as it cools, more stuff decides to short out... as the explosion propegates through the PCB. Suddenly you have char and metalization short circuits connecting the MCU as a 4000V load. its like not letting it extingush because more and more shit is connnected to the circuit as it burns. So the R of the load goes down as more and more of the meter is burned up, not to mention the plastic if cheap might char and turn conductive.Whats going to break the circuit if its 4kV connected to a expanding charcoal load that keeps finding more 'short circuit' to heat up? It needs to be contained so the R increases not decreases over time during the fireWhat I think is that they should have a meter that can take probing anything in the room. Locks can fail, signs can fall off. Lets say a sign falls off and a lock breaks. Someone can think "they opened this for me". IMO lockout is kinda BS, people and nature always messes with it... you gotta be ready for anything.The only thing thats certain is what is likely to be in a room based on the design of the building LOL, no way can you reliably predict WTF kind of BS is going down in there since then.Especially a random ass contractor. they should equip HV CAT IV equipment to all the soldiers of fortune that work for them. this ALWAYS involves contractors because they basically regularly walk into traps.If you have a contractor come into a building, chances are you don't know WTF is going on and its considered mad dangerous/tricky/hardBut the box damage is interesting. I wonder if thats just residue from the burning meter or what. Maybe the wrong kind of paint or plastic was used on the transformers? or dirty? too tightly packed ? you would think it would just burn up the meter and stop

author: calzap
author_rank: Frequent Contributor
timestamp: May 24, 2024, 09:34:19 pm
content: Quote from: Stray Electron on May 24, 2024, 08:00:03 pmAn arc flash from using an underrated meter on high voltage, high amperage equipment can destroy the meter, severely damage the surrounding equipment, and injure or kill the operator. The video linked below describes a tragic accident where a 600 V rated meter was used on 2200 V switchgear. The operator was killed. In this case, the operator was an experienced electrician, who in a temporary lapse of judgement, violated several safety rules.Mike

author: coppercone2
author_rank: Super Contributor
timestamp: May 24, 2024, 09:42:30 pm
content: Do you ever get the feeling the equipment damage is a sign that maybe something could be designed better? i understand the meter blowing up, but sometimes you figure maybe more spacing or something would have prevented it from getting so bad... like I think sometimes you would think it can be designed to kinda prevent the plasma fireball from building up so muchI generally noticed if i try to engineer anything to a standard (i.e. rackmount) it always pisses me off and I gotta make compromises that seem very inane to meet some specific size requirement.I think something must be wrong with the cabinet for it to get that damaged in the picture. and that there should be something more substantial then a label for HV transformers. Like a front facing Plaque with the voltage on it, like engraved acrylic, not something that can fall off. I can imagine now, the door hinge corroded, so they made a DIY replacement for the door without a sticker. Seems that you should label more then the cabinet

author: amyk
author_rank: Super Contributor
timestamp: May 25, 2024, 04:33:50 am
content: Quote from: Stray Electron on May 24, 2024, 08:00:03 pmIt's not just the voltage; a static shock can be over 4kV. In this case it's 4kV with a huge amount of current available, so the smallest short turns into a huge ball of plasma.

author: Stray Electron
author_rank: Super Contributor
timestamp: May 25, 2024, 12:38:27 pm
content: Another thing that I noticed was that each of the three legs in the box appear to be fused but in the After picture, the metallic center conductor of the fuses appears to be the only parts of the fuses that survived! It appears that their fuses were massively over rated and that they offered no protection at all and that is why the electrical box suffered so much damage.I wonder when and where (what country) where this happened? For a box that is supposed to contain 4,000 VAC there are no warnings on it, no insulating shields and the wires are small and appear be have only 600 volt (at best) insulation and their conductors are clearly not designed to carry the amount of current that would have been required to do this amount of damage.There's clearly a lot more at fault here than just the fact than just the fact that somebody used a shoddy meter on an HV circuit. I'm still deeply skeptical of the entire event as described. This looks more like a lightning strike on a small modest electrical panel than what was described.I for one grew up using those crappy RS meters and so did millions of other American kids but I've never seen anything like this happen because of using one. If the meters caused this kind of accidents there would have been thousands of dead wannabe electronic types.

author: Stray Electron
author_rank: Super Contributor
timestamp: May 25, 2024, 12:53:18 pm
content: Quote from: amyk on May 25, 2024, 04:33:50 amIt's not just the voltage; a static shock can be over 4kV. In this case it's 4kV with a huge amount of current availableWell that's the thing, there wasn't that much power available. Go back and look at the picture and look at the size wire coming into the top of the panel. It looks like 3 each two conductor and possibly 16 gauge so at the maximum it would have only been rated for about 15 amps of current. It could carry more current in the event of a short but not many more times more and not for more than a fraction of a second before the wire itself would have exploded. And of course, the fuses should have blownlongbefore that.

author: Haenk
author_rank: Super Contributor
timestamp: May 25, 2024, 02:40:23 pm
content: So an unexperienced apprentice is left alone working on electric HV installations, with no safety measures in place, neither on the guy nor on the installation? Plus his tool does not meet safety standards of the last 30 years (I assume the US has rather similar safety standards for professionals as in Europe.)This is indeed sad, and I certainly hope the contractor and the business do get shut down for good.

author: robert.rozee
author_rank: Frequent Contributor
timestamp: May 25, 2024, 03:16:50 pm
content: the article referred to by Mike, dated March 16, 2024, appears to be here:https://www.ecmweb.com/test-measurement/article/21283647/is-troubleshooting-considered-energized-workbut is only available to site members. however, the content seems to be from an April 1, 2020 article here:https://netaworldjournal.org/is-troubleshooting-energized-work/and can be read by anyone. this 2020 article refers back to a case history presentation:“Who’s at Fault — Owner or Contractor?” presented to the2002IEEE Electrical Safety Workshop byJoseph Andrews.given the story is true, it is very likely the apprentice applied his meter probes to the top ends of the outermost two fuses, and thus the fuses were not 'involved' in the arc event. however,the resulting explosiondestroyed the outer shells of the fuses while leaving the inner fusible elements intact. had the apprentice applied the probes to the bottom ends of the fuses, the result may well have been less severe.like others, i am (a) concerned that the apprentice was left in the situation unsupervised, and (b)horrifiedby the standard of multimeter he was using. while it was 22 years ago, i would still expect any electrical apprentice to be issued with a Fluke or similar grade of multimeter by their employer.cheers,rob :-)addendum:a reworked version of (part of) the 2020 article is located here:https://netaworldjournal.org/looking-at-nfpa-70e-2021/(see about half way down the page)this states "The apprentice technician was told only to tighten things “that were not hot.” The apprentice mistakenly used a 1,000-volt-rated tester to test a 4,160-volt potential transformer (PT) to see if it was energized". i am pretty sure the meter as identified by others isnotrated to 1000 volts!

author: CaptDon
author_rank: Super Contributor
timestamp: May 25, 2024, 03:20:19 pm
content: Stray Electron, With nearly unlimited energy from the 4160 mains once the arc flash starts it just goes and goes because the plasma has enough resistance to not trip the mains protective devices so the burning continues!!! Yes, that looks exactly like the meter initiated the event!! Your 15,000 volts at 200 amps was the pulse current not the sustained current. That would be a 3 megawatt peak pulse. What was the duty cycle, perhaps .005 max? That would be 15KW average which would be believable for a U.S.A.F. search radar from years ago. With today's quieter MMIC front ends you could search the same area with about 1/10th the pulse power of the old rigs.

author: calzap
author_rank: Frequent Contributor
timestamp: May 25, 2024, 03:23:51 pm
content: As mentioned by Robert, the “short”, i.e. the underrated meter, occurred before the fuses. No reason they should have blown. Their outer casings were shattered by the plasma blast. It is probable that upstream fuses or breakers did react. But when what is effectively a dead short is applied to conductors at 4 kV with 100’s of amps available, the usual types of fuses and breakers aren’t going to prevent an arc flash. If you’ve caused a short at more than 12 V than on anything that that was fused, you probably saw a spark at the short as the fuse was blowing. That small bit of plasma was likely harmless. Now, imagine it 100,000 or a million times larger.There is a huge safety difference in applying our common multimeters to high voltage sources like a cattle prod or even a microwave transformer versus industrial switchgear and motor controllers. Usually, on the lower current equipment, only the meter will be damaged internally. Long ago, I foolishly tried to measure the voltage of a cattle prod with a Beckman multimeter. Yup, it died but was fixable. On high voltage, high amperage sources, ordinary multimeters are bombs.Hard to know if the insulation on the three supply wires entering the back of the cabinet was rated for 4 kV. However, in the “before” picture, they are lying against the back cabinet wall, which was presumably grounded, and they look OK. The other wires in the cabinet were probably carrying relatively low (240 V or less) voltage for sensing and control. Can anyone identify the transformers?The case was presented originally at an IEEE symposium on safety and then discussed in EC&M magazine. I believe it’s a fairly accurate depiction. Watch the video; it’s happened before. On youtube and elsewhere, you can watch an arc flash occur. They can be incredibly powerful. This is why working with this kind of equipment live should be done with strong PPE and tools that can be used at a distance. And never done alone except in emergencies involving a threat to safety of people.Mike

author: jitter
author_rank: Frequent Contributor
timestamp: May 25, 2024, 03:27:06 pm
content: Quote from: Stray Electron on May 24, 2024, 08:00:03 pmI wonder if those photos were actually correct for the article. Is that wiring on the primary side of the transformers even rated for 4 kV? Somehow, I doubt it.Having said that, even low voltage can cause impressive electrical arcs as this very old but still relevant PPE demonstration video shows:Maybe not so relevant to the thread, but this shows what a failing buried MV (probably 10 kV) cable can cause:And as an extra, this video shows the impressive arc on a HV station after a human error and a failing protective device (look at how the power lines expand and sag, they even hit overhead lines of the railway network, damaging so much equipment that the rail network couldn't be used for many months):

author: CaptDon
author_rank: Super Contributor
timestamp: May 25, 2024, 03:35:08 pm
content: Even a modern day issued DMM, lets think about it?? The probe leads don't seem like they can sustain 4KV safely. Also, what if the arc flash starts inside the meter? The fuses inside the meter probably cannot interrupt 4KV. The internal fuse would probably be a plasma ball and sustain and grow!!! I have seen a plasma arc that I estimate to be over 4 feet in length travel the length of a city block between 2 of the 3 phases of an overhead 4160 neighborhood 3 phase feedline. Most folks can't even begin to understand the available plasma energy available on 4160 and 13,200 feedlines. The big problem with plasma on three phase when all three phases are part of the plasma ball is that energy is ALWAYS available unlike a single phase feed where the voltage will go through zero allowing extinguishing time. With 3 phase the arc sustains as it migrates from phase to phase following the highest available voltage. The arc rotates just like a syncronis motor!!

author: jitter
author_rank: Frequent Contributor
timestamp: May 25, 2024, 03:44:28 pm
content: Agreed. Even those incredibly expensive Bussman KTK fuses that you will find in the better multimeters (like Fluke) are rated to break 100 kA, but only at 600 Vac or less.I guess even a cat IV multimeter will blow up in your face if you were to connect it to 4 kV or higher.

author: robert.rozee
author_rank: Frequent Contributor
timestamp: May 25, 2024, 04:35:35 pm
content: Quote from: jitter on May 25, 2024, 03:44:28 pmthose fuses are only active when the meter is measuring current. when measuring voltage it is just a couple of MOVs and a fusible resistor in circuit. for example, from the schematic for the Fluke 77 series II, see below...cheers,rob :-)

author: Marco
author_rank: Super Contributor
timestamp: May 25, 2024, 05:21:42 pm
content: What actually happens to a CAT-III 600V Fluke if you connect continuous 4kV to it?

author: CaptDon
author_rank: Super Contributor
timestamp: May 25, 2024, 05:45:27 pm
content: And remember, we are not talking about some wimpy 4KV supply from a CRT flyback or CCFL inverter!! We are talking here about (looking at the picture) a cabinet fed from mains 4160 three phase that maybe could sustain 30 amps or more and on a dead short could produce probably over 1000 amps for a short duration. You could have been staring down an arc flash of over 4 megawatts or over 5000 horsepower even if for a second or two. That will ruin anyone's day!!

author: joeqsmith
author_rank: Super Contributor
timestamp: May 25, 2024, 06:35:56 pm
content: Quote from: Marco on May 25, 2024, 05:21:42 pmI assume you are asking about AC, 60/50Hz with unlimited current for all practical purposes? And with the meter set to ACV mode only?It would certainly be possible to see if a meter could be damaged using low currents without too much risk. My guess, most would be damaged but it's not something I have ever considered trying.***If you wanted to do it for real, maybe contact some of the test labs:https://ep-us.mersen.com/sites/mersen_us/files/2018-11/BR-High-Power-Test-Lab-Brochure.pdf

author: calzap
author_rank: Frequent Contributor
timestamp: May 25, 2024, 06:50:40 pm
content: Quote from: joeqsmith on May 25, 2024, 06:35:56 pm4kV with unlimited current is what happened in my original post. Wouldn't have mattered if it had been a Fluke instead of an RS meter. Up to 600 V with effectively unlimited current ... OK. Beyond 600 V with unlimited current, you're holding a bomb.Mike

author: Marco
author_rank: Super Contributor
timestamp: May 25, 2024, 07:14:44 pm
content: Quote from: calzap on May 25, 2024, 06:50:40 pmWith 1 Meg series resistance to the input voltage limiting, it's going to burn through pretty fast. With a couple Watt 10 Meg series resistance and assuming the selector switch and PCB don't arc over, it could probably hold off the voltage indefinitely.I think it's 1 Meg though.

author: calzap
author_rank: Frequent Contributor
timestamp: May 25, 2024, 08:35:36 pm
content: Quote from: Marco on May 25, 2024, 07:14:44 pmDo you really think you could apply a continuous 4kV with essentially unlimited current to the input of any regular multimeter of any brand without internal arcing? Doesn’t matter if a resistor is 1 gigohm if it arcs over. With that kind of current, any tiny arc will almost instantly grow to catastrophic proportions.Mike

author: coppercone2
author_rank: Super Contributor
timestamp: May 25, 2024, 08:59:05 pm
content: what does this table mean?it says 12kV for a 1000V rated meter, and 8kV for a 600V CAT IV meter. It says for impulse thoughhttps://www.flir.com/discover/professional-tools/what-do-cat-ratings-mean/would the 1000V rated CAT IV meter still explode like that?And it made me wonder, if you can't fuse it there, I wonder if they could make a advanced AFCI that actually detects where the arc is. Like a arc TDR. I know they expect some arcing with HV circuits, maybe you can determine if arcing is happening in the correct location and shut it down if its not? If it had a resolution of a foot to determine if its in the switch or if its in the transformer case.

author: shapirus
author_rank: Super Contributor
timestamp: May 25, 2024, 09:05:58 pm
content: Quote from: calzap on May 25, 2024, 08:35:36 pm"If it arcs over" is key. The question is, will it?

author: joeqsmith
author_rank: Super Contributor
timestamp: May 25, 2024, 09:10:52 pm
content: Quote from: Marco on May 25, 2024, 07:14:44 pmWell, you did mention Fluke brand and not the bottom end. I'll remind you of someone that had told me about how my testing was damaging the meter's MOVs. I ran a test with a few kV for days measuring the current. Person did not understand that the PTCs and series resistors limit what the MOV is exposed to.To be clear, there is typically a surge rated resistor in series with a large body PTC in series with some MOV combination. The 1M you mention is basically looking across the MOVs. Clamped typically under 2kV. So, say 2.5kV across the surge rated resistor and PTC. As the PTC heats (which it would in this condition) the voltage drop across it will increase. I doubt very much that the 5mm PTCs I typically see in the low end meters would survive but I really have no feel for the large parts I see in the Fluke meters.It's certainly possible to check it (safely ish... sort of... assuming you have some idea what you are doing and take precautions.)

author: Marco
author_rank: Super Contributor
timestamp: May 26, 2024, 12:03:57 am
content: Quote from: calzap on May 25, 2024, 08:35:36 pmIt already has to hold it off for a bit for CAT-III 600V. How long exactly? (I haven't read the standard.) If it's microseconds it likely won't arc, but if it's milliseconds and it can arc it will arc already.It's not like the distance needed to hold off 4kV across a clean PCB is huge.

author: Someone
author_rank: Super Contributor
timestamp: May 26, 2024, 12:42:14 am
content: Quote from: Marco on May 26, 2024, 12:03:57 amQuoteDifferent limits for the different testing regimes. But transient overvoltage is only over the 1,2/50 μs waveform.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 26, 2024, 12:49:46 am
content: Standard surge is 50us FWHH. For 4kV, I test using 100us FWHH with a 2ohm source, limited to about 15J.I had tested that Fluke 101 using 13KV peak, 100us FWHH, 2 ohm source and it was not damaged. A member here repeated the test using an actual combo generator following the IEC standards and saw no damage as well.Still, there's a big difference between that and 50/60Hz 4kV. With a 100us FWHH, I doubt the PTC would even respond. So the voltage across the two (surge rated resistor and PTC) will more closely match. Not the case with the low voltage AC mains.I would never suggest that the Fluke 101 would survive it without running at least some minimal test..

author: robert.rozee
author_rank: Frequent Contributor
timestamp: May 26, 2024, 03:54:31 am
content: Quote from: joeqsmith on May 26, 2024, 12:49:46 ami'd certainly not expect any meter to survive it, but rather to be able to contain/absorb the 'event'.attached below is the full schematic of the Fluke 77 series II. from this one can see that R2/E1 are largely there to protect the OHS pin of U1 (if S1 is closed) and pins 11 and 10 of S1 (if S1 is open). at 1500v (E2 strikes) R2 would see approximately 1.5 watts, at 4kV it would see 16 watts; even at this power level i would expect it to survive for a few seconds,assumingit did not arc over.the main show involves R1, RV1 and RV2.to have any hope of containing/absorbing a 4kV continuous input i would suspect thatbothR1 (1k ohm)andR2 (1M ohm) would each need to be split across multiple parts that were good for 1kV each. it would then be necessary to add a fuse in series with the 'V/O HI' input connector such that our new fuse:(a) was essentially rated at near to zero current. ie, a "10mA fuse",(b) could break 4kV and contain/extinguish the resulting plasma,(c) would go open prior to the R1 (1k ohm) combination overheating.R1 would no longer need to be a fusible part, as our "10mA fuse" would replace this function.now all these changes would add size to the meter, as well as cost. plus, they wouldn't help if our user tried to measure 10kV.i'd still be keen to know how a bog-standard Fluke 77 reacted to a 4kV continuous inputcheers,rob :-)

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 26, 2024, 05:02:29 am
content: Quote from: robert.rozee on May 26, 2024, 03:54:31 amIf the current can be sufficiently limited, that's surprisingly easy based on the videos of hobbyists playing with neon sign transformers. Probably would make most sense to have that fuse be in the probe, one design that would be sensitive enough would be a high voltage resistor soldered to a spring that would pull apart when it melts, with some sort of dielectric liquid to quench the arc. At the same time, it needs to give a visual indication that it has blown to not create another hazard of the meter silently indicating no voltage.

author: calzap
author_rank: Frequent Contributor
timestamp: May 26, 2024, 05:14:32 am
content: In the video of the Eddie Adams accident, he was using a multimeter rated at either 600 or 1000 volts (both values are mentioned in the video). The voltage he applied it to was mentioned as 2200 or 2300 volts; however, the equipment can be seen to have a label of 2300 volts. The multimeter was almost certainly a Fluke. Perhaps someone can identify the charred remains as a Fluke. However, the electricians interviewed appear to be holding a Fluke at times. The electrician doing the reenactment appears to be holding a Fluke. They all worked for the same company; so likely all the company’s electricians were issued Flukes. Someone familiar with Flukes can probably identify the model(s).So, a Fluke rated at either 600 or 1000 V was applied to a continuous voltage of 2300 volts with huge current available. And it exploded.Mike

author: johansen
author_rank: Super Contributor
timestamp: May 26, 2024, 06:18:17 am
content: I have a capacitor bank which can be configured for 80uf at 8kv or 320uf at 4kv.Its not enough to shrink quarters but it can bend them, self resonant frequency is 50khzPlease send me expensive test equipment to blow up.

author: coppercone2
author_rank: Super Contributor
timestamp: May 26, 2024, 06:26:51 am
content: I think the one in the picture is thishttps://www.ebay.com/itm/175764036511

author: johansen
author_rank: Super Contributor
timestamp: May 26, 2024, 06:42:19 am
content: Quote from: CaptDon on May 25, 2024, 05:45:27 pmYou are off by a couple orders of magnitude.An average 120/240 system on a larger building has a short circuit current of 10,000 amps depending on the size of the pole transformer and length do the utility drop. My parents house had a short circuit current around 5ka4000 volt systems are typically fed from 100Kva and larger transformers of 4 to 10% impedance. Lets say a 10 megawatt transformer and 6% impedance, your short circuit current is 30 to 50,000 amps. Which my capacitor bank can do, for about 20 microseconds.

author: jitter
author_rank: Frequent Contributor
timestamp: May 26, 2024, 07:52:16 am
content: Quote from: robert.rozee on May 25, 2024, 04:35:35 pmThat is very true, and normally DMMs don't use fused probes. And to be honest, I totally forgot about this. But I'm pretty sure that a high enough voltage (maybe not 4 kV, but probably 10 kV and higher) will have no problems destroying those wimpy MOVs and strike and sustain an arc across the pcb and the air where lower voltages would not have the 'reach' to do so.Fused probes are available, however, and come as standard on power quality analyzers like the Fluke 1775. I still don't think those fuses will be rated high enough when it comes to high voltages. The fuses in our 10 kV grid are about the length of my under arm.

author: jitter
author_rank: Frequent Contributor
timestamp: May 26, 2024, 07:54:53 am
content: Quote from: Marco on May 25, 2024, 05:21:42 pmOK, not continuous 4 kV but 1 ms discharges, our own Dave has made a video in his early days that may be of interest:This is done at 400 J per discharge and hence looks underwhelming. But you can probably imagine that continuous exposure (and hence sustained arc) is going to be a bit more impressive and maybe those pictures are actually correct for the article, after all.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 26, 2024, 08:59:20 am
content: Quote from: robert.rozee on May 26, 2024, 03:54:31 amThe Fluke 77 is a very old meter. Fluke and other companies improved their input designs as I mentioned.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 26, 2024, 09:03:52 am
content: Quote from: johansen on May 26, 2024, 06:42:19 amThe highest ASCC I measured in our home for the 110 outlets was 0.39kA.https://www.eevblog.com/forum/testgear/trashy-meters-redux/msg4835948/#msg4835948

author: joeqsmith
author_rank: Super Contributor
timestamp: May 26, 2024, 09:49:19 am
content: Quote from: jitter on May 26, 2024, 07:54:53 amWhen looking at the Fluke 28, he points to the large PTC and identifies it as a MOV, that is basically the front end I would expect to see.https://youtu.be/M-FZP1U2dkM?t=663But is does seem to suggest that a modern Fluke would not survive at 4kV 50/60HzQuote from: calzap on May 26, 2024, 05:14:32 amAs I mentioned, Fluke hasn't remained stagnant. Some of their old products could easily be damaged.Looking at my own tests, I ran 1.6kVDC into a modern Fluke for several minutes while monitoring the current. I think the MOVs were rated to 800 ea. So now we are only talking about 700V across the PTC and surge rated resistor. Seems like it might survive.700V/2500 Ohms or about 280mA. My DC supplies would all fault out before the PTC would start to heat up.

author: jitter
author_rank: Frequent Contributor
timestamp: May 26, 2024, 12:12:34 pm
content: DC power supplies are one thing, but the grid another.A (e.g.) 10 kV distribution ring is protected by relais that receive data on current (and sometimes also voltage) from transformers, so a secondary measurement. When an overcurrent fault is detected, there's a preset time that needs to expire before the protection kicks in and operates a switch to isolate the circuit.The further away from the main station, the shorter these delay times. This is done to create selectivity in order to have the least amount of customers lose service when a fault occurs. Basically, these delay times are staggered and could end up being as long as 2 seconds but no shorter than 300 ms.Cables and switchgear must be rated to carry short circuit currents for this amount of time. A 1 ms discharge of 400 J is enough to blow up a DMM, how about 2 seconds of continuous discharge.These protection relays are there to prevent damage to equipment directly and personal injuries or death indirectly. They cannot protect against someone probing with the wrong equipment.When you look at the specs of multimeters supplied by the manufacturers, they simply tell you the max working voltage you can use it on. The CAT ratings taketransientspikes into account, depending on the use (and that depends on the source impedance, the lower, the higher the cat rating).I am required to have a cat IV meter for my work. Measuring high voltages (or rather: proving live or dead) are done with capacitive testers like the Pfisterer KP-5 Test on a long stick. Basically a Voltstick on steroids.

author: johansen
author_rank: Super Contributor
timestamp: May 26, 2024, 02:56:10 pm
content: Quote from: joeqsmith on May 26, 2024, 09:03:52 amAt 4000 volts the resistance of your 100 feet 14ga wire is negligible, and the short circuit current is 16,000 amps instead of 480 on 120vac. Ive shorted 120vac outlets out while changing them live, and didnt even see the spark when the breaker trips.Not sure why you thought to add to the conversation.As for dmms, ive put 2000 volts across two 10m ohm input dmms and they survived a long time.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 26, 2024, 03:40:06 pm
content: Quote from: johansen on May 26, 2024, 02:56:10 pmI don't have 4kV running to the house. 240 single phase is common.Quote from: johansen on May 26, 2024, 02:56:10 pmBecause you claimed to have measured more than 10X higher at your parents home.Quote from: johansen on May 26, 2024, 02:56:10 pmI will assume what you are describing is two meters in series. That should come as no surprise, assuming the two meters are well matched so the voltage balances evenly.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 26, 2024, 03:48:23 pm
content: Quote from: johansen on May 26, 2024, 06:18:17 amI've actually had people claim this is how I test hand held meters (connecting them directly to a bank of capacitors). In my case, I shape that waveform without a meter attached. If I were only charging up a bunch of caps with only the meters at the load, it's more like pushing DC through them (if they don't break down).

author: zapta
author_rank: Super Contributor
timestamp: May 26, 2024, 04:30:31 pm
content: Quote from: Stray Electron on May 24, 2024, 08:00:03 pmDid you use to clap behind the back of people working on high voltage?We did.

author: temperance
author_rank: Super Contributor
timestamp: May 26, 2024, 05:15:16 pm
content: QuoteHow funny. I had a colleague who like to do just that when I was working on a 5 kW +200 -200 V SMPS. He tried it twice. The third time I pushed him into a cabinet. He told me I wasn't normal.Later on he electrocuted himself by grabbing the busbars of 3 phase powered system while the thing was still plugged in. One burned tendon later, he's probably still having trouble masturbating.

author: Marco
author_rank: Super Contributor
timestamp: May 26, 2024, 05:37:12 pm
content: Quote from: joeqsmith on May 26, 2024, 09:49:19 amSo to hold off the allowed transient indefinetely you'd either need a large string of PTC's in series, or disconnect the ohm/diode path with the selector switch. Also the series resistance for the Voltage path to the MOV's would need to be 10+ Meg to keep dissipation reasonable. Doable, but maybe not having the meters blow up until even more dangerous voltages would just cause more dangerous behaviour.

author: Harry_22
author_rank: Frequent Contributor
timestamp: May 26, 2024, 06:44:04 pm
content: I was somehow struck by Wimshurst machine while having fun.The next day I was admitted to the hospital with atrial fibrillation.

author: jitter
author_rank: Frequent Contributor
timestamp: May 26, 2024, 07:30:20 pm
content: Quote from: joeqsmith on May 26, 2024, 03:40:06 pmAnd why not? It all depends on the impedance of the wiring between your distribution board and the transformer.I live pretty close to a distribution station, but the people living right nextdoor have a (calculated) wiring impedance of just 23 mΩ. If my calculation is correct, then they should have a short circuit current of about 10 kA at their board.

author: coppercone2
author_rank: Super Contributor
timestamp: May 26, 2024, 07:52:30 pm
content: making decisions not based on the standards is a bad idea even if your current is lower because the power co can always change things, especially with EVs and stuff requiring more power. you might have a drastically changed situation if they do upgradesI.e. i see in pheonix they put these ugly ass towers up for mains to support grid load on AC and EV where there is not enough local storage and very high peak demands. they might be getting some scary fault currents there now. it looks like thick 'pylons' in a residential neighborhood in peoples backyards.

author: SeanB
author_rank: Super Contributor
timestamp: May 26, 2024, 08:06:23 pm
content: I have seen a Fluke 77 that was returned "under warranty" because the arctrician tried to measure the primary side of a 11kV distribution transformer, and just grabbed the meter, and a long stick ( some thought there) to hold the probe near the connection. Inside the case was copper plated all the way down from display to input jacks, and there was no more copper on the board, other than the copper by components under the soldering. All blown off the soldermask, leaving bare board behind. Meter did not power on at all, the Fluke ASIC was there, missing the top of the package, and the thick film resistor network was cracked, and the resistors in it had marks of flash over on them for the input side one. Fuses were intact, along with the 9V battery, and the display was still working, put into another meter to verify, as that one was there because they had broken the display. Meter was scrapped, and the broken leads were also cut to pieces. New meter sent, along with the bill. I was still in school, visiting the one place that was a RS distributor (when RS catalogues were still the only way to get data sheets or more exotic IC's, and a 2 week wait for them to arrive) and which is still running these days.By me the distribution transformer (200kVA, is 50m away, 300m cable wise, and the cable itself probably dates from 1900 in places, being the original paper insulated cable, and the feed to me is only around 60 years old, well worn SWA paper insulated and oil filled, complete with lead wiped ends. 400A fuses by the substation, a standard size, though there are still a good number with 200A fuses, that date from the 1950's, still in use, only replaced when they blow, and they will not blow for 400A of load as evening peak, measured that one evening.

author: 44kgk1lkf6u
author_rank: Regular Contributor
timestamp: May 26, 2024, 10:42:16 pm
content: Quote from: zapta on May 26, 2024, 04:30:31 pmWhy? Was it to scare them?

author: johansen
author_rank: Super Contributor
timestamp: May 26, 2024, 11:00:10 pm
content: Quote from: 44kgk1lkf6u on May 26, 2024, 10:42:16 pmwe had no tolerance in the usmc for that bullshit.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 26, 2024, 11:59:59 pm
content: Quote from: jitter on May 26, 2024, 07:30:20 pmSorry, why not what?

author: joeqsmith
author_rank: Super Contributor
timestamp: May 27, 2024, 12:15:42 am
content: Quote from: Marco on May 26, 2024, 05:37:12 pmThat HV probe I made up for example is 400Meg but the resistors have a limited life. Using non-contact would be better.

author: johansen
author_rank: Super Contributor
timestamp: May 27, 2024, 12:18:54 am
content: Quote from: joeqsmith on May 26, 2024, 11:59:59 pmthis ain't your grandma's outlets.a typical industrial 120/208 system has a 10,000 amp fault current, and on industrial buildings they stencil the short circuit current on the panel.. -of course if you add in .25 ohms from 100 feet of 14 gauge wire then the short circuit current drops to what you measured, 390 amps.but lets imagine you now have a 4000 volt service. suddenly that additional .25 ohms doesn't really do much to limit the current! not to mention the wires in a 4000 volt system will likely be nothing less than 6 gauge.my house drops 4 volts at 60 amps, for a 3600 short circuit current, i'm about 60 feet of 4/0 aluminum cable direct to a pad mount 25kva transformer.Attached is a photo of the transformerThose wires sticking up out of the ground are live. I was able to stab them with my multi meter leads and measured a 3.6 volt drop at a 63 amp load.meaning 90% of the voltage drop is in the transformer. this is typical of a 25kva transformer.my neighbor had the power cut to her shed (it was a separate utility drop) i'm pretty sure they decided to just dig up the line and cut the cable and cap the ends, rather than pull the meter (which they didn't) --i've never seen bare wires left up out of the ground like this before but prior to this thread i wasn't inspired to mess with them.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 27, 2024, 12:25:36 am
content: Quote from: johansen on May 27, 2024, 12:18:54 amI'm sure your trying to make a point but it's lost on me. I provided the data I collected from our home for a reference. This was measured not calculated. I've already explained there is no 4000V service feeding into our home.

author: johansen
author_rank: Super Contributor
timestamp: May 27, 2024, 12:29:02 am
content: Quote from: joeqsmith on May 27, 2024, 12:25:36 amthe whole point of this thread regards why electrical meters blow up at 4000 volts.turns out 20,000 amps will do it?somehow you're not convinced that could happen?

author: joeqsmith
author_rank: Super Contributor
timestamp: May 27, 2024, 12:35:08 am
content: Quote from: johansen on May 27, 2024, 12:29:02 amI think you're reading more into my posts than what is there is all.

author: Monkeh
author_rank: Super Contributor
timestamp: May 27, 2024, 12:36:00 am
content: Quote from: joeqsmith on May 27, 2024, 12:25:36 amThe 5kA mentioned before would be between both legs of the phase, at 240V, at the origin of the installation. Whether you have 4kV at home or not isn't really relevant to his post.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 27, 2024, 12:38:15 am
content: Quote from: Monkeh on May 27, 2024, 12:36:00 amHe never posted how it was measured or at what location. I did provide that detail.

author: johansen
author_rank: Super Contributor
timestamp: May 27, 2024, 12:42:37 am
content: Quote from: Monkeh on May 27, 2024, 12:36:00 amThis is all turning into a gigantic waste of time, but at least i was inspired to find out if the wires sticking up out of the ground on my neighbor's side of the road are live.100 feet of 14 gauge wire (50 feet from your panel) is enough resistance that you can safely touch the wires together in front of your face and you will not be blown across the room by the expanding metal vapor cloud at 50,000 degrees kelvin!here is a classic 480v clip

author: joeqsmith
author_rank: Super Contributor
timestamp: May 27, 2024, 12:57:39 am
content: It's not like we have not discussed fault currents and arc flash before. Normally I have no interest but I am still curious about Marco's original question, which is what prompted me to post.

author: johansen
author_rank: Super Contributor
timestamp: May 27, 2024, 01:05:31 am
content: Quote from: Marco on May 25, 2024, 05:21:42 pmi fully expect it to explode.two cheap meters, a VC-99 and an older 2000 count meter survived 1999 volts on a slow rise time, but the 2000 count meter blew up when i reversed the polarity suddenly. -pretty sure i did not test the vc-99 the same way after the other one blew up.

author: Someone
author_rank: Super Contributor
timestamp: May 27, 2024, 02:08:58 am
content: Quote from: joeqsmith on May 27, 2024, 12:57:39 amOrly? how about the post quoted in full:Quote from: joeqsmith on May 26, 2024, 09:03:52 amSo you've cherry picked a lowball number as some argument against people discussing significant fault currents possible in residential/commercial installs. Pretty much exactly the same as the linked thread.Why go on replying and arguing? Some installs have significant fault current available, some don't. But they're not specifically labelled or decorated differently (in most locations) so people need to treat them as worst case unless otherwise proven.

author: coppercone2
author_rank: Super Contributor
timestamp: May 27, 2024, 02:50:43 am
content: Quote from: johansen on May 27, 2024, 12:42:37 amwhat is the current going on there? It looks like you combined about 40 or more high current stick welding arcs. That is gotta be like a few pounds of black powder going up in your face

author: coppercone2
author_rank: Super Contributor
timestamp: May 27, 2024, 02:59:59 am
content: does it do the jacobs ladder thing with multimeter leads?Do the HV meters have like 40AWG meter leads for this purpose?

author: joeqsmith
author_rank: Super Contributor
timestamp: May 27, 2024, 03:02:43 am
content: Quote from: Someone on May 27, 2024, 02:08:58 amI wasn't aware of any arguments. Rather I just provided a few measurements.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 27, 2024, 03:13:57 am
content: Quote from: johansen on May 27, 2024, 01:05:31 amI'm surprised you could apply 2kVDC into the VC-99 without damage. Was in the DCV mode only?I've never tested a meter with enough energy to make one explode. Worse case, I think a case once split open.

author: jitter
author_rank: Frequent Contributor
timestamp: May 27, 2024, 06:00:27 am
content: Quote from: SeanB on May 26, 2024, 08:06:23 pmWell, that confirms my expectations what will happen when a DMM is subjected to high energy high voltage supplies like the MV part of the grid is. I don't think even a modern day Fluke will behave differently, the creepage distances inside are simply too short.Off topic: that paper insulated cable, does it look anything like the picture below? If so, then they might not be as old as you think. Even though they have been superseded by XPLE cables, over here, production was stopped as late as 2005.For hose who don't read Dutch, from top to bottom it says: copper cunductor, conductor isolation, common isolation, lead ply, burlap ply, double iron ply, double burlap ply.The conductor isolation is made from paper and impregnated with oil. The burlap layers are impregnated with oil, wax and tar. At the termination point, these cables stick out of the soil vertically into the station and and are terminated in enclosures filled with oil that should be kept topped up.The outer layer of the cable also contains chalk, but has mostly rotted away by now. It's estimated our grid still has about 50% of this old style cable in it and continues to be in service just fine. Medium voltage cables in this style can also be found with aluminium conductors instead of copper.

author: jitter
author_rank: Frequent Contributor
timestamp: May 27, 2024, 06:18:39 am
content: Quote from: joeqsmith on May 26, 2024, 11:59:59 pmThe answer to that question was given in the same post (please quote it in its entirety, not just this question), 5 kA of short circuit current is perfectly possible in a residential situation but depends on the impedance of the grid at the connection. A 400 V threephase service, which almost everyone has over here by default, is capable of 10 kA short circuit current when there's only 23 milliOhms of impedance between the transformer in the station and the distribution board in the house. Obviously, the house wiring adds impedance, and depending on wire diameters and lengths, this will lower short circuit current some more.At the other extreme, 283 milliOhms are allowed (at the board) for a 3 x 25 A service which lowers the short circuit current to 0.816 kA. This must not be any lower otherwise protective devices may react too slowly or not at all.

author: SeanB
author_rank: Super Contributor
timestamp: May 27, 2024, 10:01:35 am
content: Quote from: jitter on May 27, 2024, 06:00:27 amYes, but those I do know the install date, because they are the original ones installed for the long removed tramway, and the one for the building is the original installed 70 years ago when it was built. Though it is very likely the cable buried underground no longer has any of the steel strap wrap left on it, and there is a good chance the lead is the only thing keeping the water out of the cable Just like the paper insulated phone cables, also around a century old, and likely the 200 pair bundle is now down to around 50 usable pairs, though of course finding any place that actually still uses copper phone service is getting rare, as the encumbent telco is officially no longer doing cable repairs, and has retrenched all the tech staff in that division, and they will simply sell you a mobile phone and port the number, "for free", once you sign a 36 month contract for it. If you had DSL tough, unless it was with them as well, in which place you also sign an additional 36 month data contract, with caps on it.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 27, 2024, 01:48:04 pm
content: Quote from: jitter on May 27, 2024, 06:18:39 amYou are trying to ask me a question but are not sure how to ask it, and you already have an answer?

author: Kim Christensen
author_rank: Super Contributor
timestamp: May 27, 2024, 02:49:32 pm
content: Quote from: jitter on May 27, 2024, 06:00:27 amI can't read Dutch, but in this case I prefer the Dutch words to the English ones.