Author Topic: Has anyone ever megged a multimeter ? (HV testing)  (Read 5890 times)

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Offline tooki

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Re: Has anyone ever megged a multimeter ? (HV testing)
« Reply #25 on: January 24, 2025, 05:09:56 pm »
There is widespread agreement here that we would welcome multimeter manufacturers being honest about little meters without CAT ratings. There is absolutely a place for those meters.

What is inexcusable is lying about CAT ratings, because it could put someone in danger, for example if some unwitting buyer at a power company buys fake-CAT-rated meters for the company’s linemen who actually are working on dangerous high-energy circuits. The fake paper trail makes it seem the meters are suitable, and the guys using them are at serious risk if something goes wrong. Those meters might have been perfectly safe for 99% of buyers, but not for those linemen.

Well, the fact that the budget meters do not comply with their declared standards would have to be proven in individual cases.
It is usually simply assumed in this forum.
No, it isn’t just assumed.

When you see a meter with a 250V AC 5x20 (or 5x10!) glass fuse, you know it is by definition not compliant. When you see one with no fuse at all (on the current ranges), you KNOW it isn’t compliant! When you see a meter with input PCB traces with a screw running between them, using up all of the space between the traces (such that it is almost shorting them out) you know there is no way it could pass CAT rating testing. When you see a meter that explodes when subjected to the CAT rating’s test conditions, you know it isn’t compliant.

There do exist properly CAT-rated meters without fuses: meters without current ranges. ;)

I mention fuses a lot because they’re an easy first sign of… effort. Do you think the big manufacturers would use cheaper fuses if they could, and still meet the stated rating? Of course they would. It’d be cheaper for them and less annoying for users. So the fact that the big names use the $$$ fuses is a strong indicator that the CAT ratings cannot be met without those fuses.

But it’s not just fuses: if a meter lacks real input protection, it’s not likely to meet CAT ratings. Again, we see what the big names do (adding things like gas discharge tubes and other overvoltage devices), which the cheap brands leave out, and which the big brands would leave out if not necessary.

And there are meters that, regardless of CAT rating printed on them, do clearly make more effort than others, because of using better fuses (like British-standard ceramic mains fuses), and having decent input protection otherwise.



I don't know enough about it.
Which is why it’s really, really annoying that you keep inserting yourself into those discussions, declaring that everyone else is exaggerating the risks. You don’t know nearly enough about the subject to be lecturing everyone else about it! Your ignorance is not of equal value as others’ expertise!!

But yes, as Dave Jones said, the CAT I and II declarations on the front of a meter will be removed in future anyway.
It’s bizarre to me that they decided to eliminate the lower categories. :/

That would be a good opportunity to do away with dubious CAT ratings completely.
How would it? The problem is that cheap meter makers always slap either CAT III or IV on meters, even ones that very obviously cannot meet those ratings.

Personally, I am interested in other things, such as accuracy and precision/resolution, measuring range etc. etc.
I have never bought a DMM because of CAT ratings.
And that is absolutely fine. But it’s irresponsible to tell everyone else here that they don’t need to observe CAT ratings either, and it’s absurd to basically insult people who try to take a more nuanced position.
 
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Online bdunham7

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Re: Has anyone ever megged a multimeter ? (HV testing)
« Reply #26 on: January 24, 2025, 05:12:43 pm »
Well, the fact that the budget meters do not comply with their declared standards would have to be proven in individual cases.
It is usually simply assumed in this forum.

It isn't just simply assumed, or at least it wasn't until there were plenty of examples and evidence.  Then there appears to be some differences in how those standards are interpreted, specifically whether the requirement is that the meter simply not blow up or whether it should continue to operate.  Certain manufacturers have shown specific contempt for the standards by simply omitting the relevant components when selling the meters in markets where there is little inspection or enforcement or by selling the exact same meter in one jurisdiction with much higher ratings then ones sold somewhere that cares.  Others have been found to have submitted samples for certification and then selling meters that aren't not manufactured as the samples were.  So if CEM, Uni-T, Zotek or whoever print a CAT rating on their meter I'm not going to give them the benefit of the doubt.

And old thread discussing this, with examples:

https://www.eevblog.com/forum/testgear/a-list-of-multimeters-that-do-not-appear-to-meet-their-claimed-safety-specs/msg157700/#msg157700
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 
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Online Aldo22

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Re: Has anyone ever megged a multimeter ? (HV testing)
« Reply #27 on: January 24, 2025, 05:23:24 pm »
And that is absolutely fine. But it’s irresponsible to tell everyone else here that they don’t need to observe CAT ratings either, and it’s absurd to basically insult people who try to take a more nuanced position.
I am not insulting anyone.
I just think that CAT ratings are irrelevant for most electronics hobbyists and that a budget meter can have other advantages and you shouldn't reject these devices simply because of their (dubious) CAT ratings.
And I also clearly stated that you should buy professional gear beyond CAT II.
Let's not get carried away.
 

Offline tooki

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Re: Has anyone ever megged a multimeter ? (HV testing)
« Reply #28 on: January 24, 2025, 05:47:30 pm »
And that is absolutely fine. But it’s irresponsible to tell everyone else here that they don’t need to observe CAT ratings either, and it’s absurd to basically insult people who try to take a more nuanced position.
I am not insulting anyone.
I just think that CAT ratings are irrelevant for most electronics hobbyists and that a budget meter can have other advantages and you shouldn't reject these devices simply because of their (dubious) CAT ratings.
And I also clearly stated that you should buy professional gear beyond CAT II.
Let's not get carried away.
Suggesting that being concerned about safety is “FUD”, and insinuating that everyone who concerned themselves with safety was spreading it, could certainly be interpreted as insulting:
Many times, people ask without specifying what their use case is. Until we know that it is a low-energy application, we err on the side of safety.

Yes, but the title of this thread says it's about “budget multimeters” and immediately you're back to Fluke, Brymen and fuses, which cost more than 5 “budget multimeters”.
Does it always have to be like this?

I also can't shake the suspicion that this is often about advertising.
The term “FUD” always comes to mind in this context.

"The aim is to create fear, uncertainty and doubt in the recipient of the information (e.g. customers, voters) about a competitor or its products (propaganda). This exploits the fact that people's feelings of fear are irrational and that even demonstrably false information can lead to uncertainty."

But well, the topic keeps coming up here...
The “boss” has also commented on this.


And before that you said:
But as I said, I suspect that this problem is massively exaggerated in this forum and plays virtually no role statistically.
Or to put it another way: if you were to recommend that the hobbyist buy an AN870 instead of a Fluke and use the difference to buy some running shoes or healthier food, you would probably have “saved more lives”.  ;)

Those are some bold statements from somebody who doesn’t
know enough about it.
 
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Online joeqsmith

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Re: Has anyone ever megged a multimeter ? (HV testing)
« Reply #29 on: January 24, 2025, 05:57:46 pm »
And that is absolutely fine. But it’s irresponsible to tell everyone else here that they don’t need to observe CAT ratings either, and it’s absurd to basically insult people who try to take a more nuanced position.
I am not insulting anyone.
I just think that CAT ratings are irrelevant for most electronics hobbyists and that a budget meter can have other advantages and you shouldn't reject these devices simply because of their (dubious) CAT ratings.
And I also clearly stated that you should buy professional gear beyond CAT II.
Let's not get carried away.



...And with a ZT-225, not even that happens....
The sturdy structure alone with the fat, slightly elastic holster simply does not allow it to “blow to smithereens” (attachment).

I have never attempted to blow a meter to smithereens.  When designing the transient generator I use to evaluate the meters, I purposely limited the amount of energy (again, I was never interested in safety).   I have seen some meters that will breakdown during my testing or supplied with glass fuses.  For these special meters, I will apply the HV transient (enough to cause the meter to arc and develop a low impedance path) and then inject enough energy to simulate a half cycle of AC (about 600J max).   Not a lot, but enough to provide some idea of what could happen. 

It would be interesting to see an accredited lab run independent tests on meters.  Till that time comes, I guess take what I show for what it is.  All meters tested to limited low energy sources.

Online Aldo22

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Re: Has anyone ever megged a multimeter ? (HV testing)
« Reply #30 on: January 24, 2025, 06:06:40 pm »
@tooki: Please calm down a bit. It's not that important, is it?  ;)

Maybe I have no idea, but Dave Jones is heading in the same direction:

Multimeter safety is a tad overrated, and has been pushed toward the extreme end of the OH&S spectrum.
That's not a bad thing of course, in fact it's great, but people do get a tad carried away.
Sure the general recommendation of "CAT III for anything mains related and above" is good general advice, but it's not needed.
Most people do not work on such high energy systems to warrant being that worried about it.
And basically it's limited to only one fault scenario, probes in the A jack by mistake when measuring mains or another high energy system.
The whole peak overload thing (e.g lighting strike on the mains) is so remote an issue that it's almost not a thing.

And by the way, have a nice evening!
I have to go now.
« Last Edit: January 24, 2025, 06:09:01 pm by Aldo22 »
 

Online joeqsmith

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Re: Has anyone ever megged a multimeter ? (HV testing)
« Reply #31 on: January 24, 2025, 07:22:53 pm »
Is Dave the gold standard for all advice?

Offline Gyro

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Re: Has anyone ever megged a multimeter ? (HV testing)
« Reply #32 on: January 24, 2025, 07:38:39 pm »
I really hope not!  >:D
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Offline tautech

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Re: Has anyone ever megged a multimeter ? (HV testing)
« Reply #33 on: January 24, 2025, 07:42:18 pm »
Is Dave the gold standard for all advice?
Certainly not.

The standards are.
My last hobby DMM purchase was a Fluke 15B that does all I need and has provided many years of service.
Fluke 106 were given to my 2 sons last Xmas and I know that investment will protect them.....
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Online bdunham7

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Re: Has anyone ever megged a multimeter ? (HV testing)
« Reply #34 on: January 24, 2025, 10:15:46 pm »
If your gonna use a megger then at least use a megger thumper not a piddle little 1000v megger insulation tester

https://www.megger.com/en-us/products/ez-thump-12-kv-model-v3-cable-fault-location-system

I especially like the arc-reflection TDR feature!  Now imagine you've left your DMM connected on the other end when you "thump" the cable.
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Online joeqsmith

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Re: Has anyone ever megged a multimeter ? (HV testing)
« Reply #35 on: January 24, 2025, 10:46:37 pm »
If your gonna use a megger then at least use a megger thumper not a piddle little 1000v megger insulation tester

https://www.megger.com/en-us/products/ez-thump-12-kv-model-v3-cable-fault-location-system

I especially like the arc-reflection TDR feature!  Now imagine you've left your DMM connected on the other end when you "thump" the cable.

I doubt many typical CAT III/IV rated handheld meters would survive.   500J is on par with my low voltage generator but at 12kV, that's a lot of stress.  Try it with your meter of choice and report back....  :-DD

Offline Sensorcat

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Re: Has anyone ever megged a multimeter ? (HV testing)
« Reply #36 on: January 25, 2025, 02:00:17 am »
The only place where something could happen is the 20A input with ceramic fuse.
But the circuit breakers are at 16A in our house. What comes first?
This nonsense-assertion (in more than one way) alone is the proof that you should stop spreading your new religion over the forum!

The real danger is this:

The usual beginner that asks for DMM-selection advice starts like "I need a DMM, what should I take for my work, primarily Arduino stuff?" Means: "I do not exclude anything, just want to mention what I usually do." Being bold after a while, having developed impressive half-knowledge on Arduino stuff, he thinks that an electrician is no longer needed for fixing stuff in his house. It's the same kind of being bold with half-knowledge that makes YOU, Aldo22, lecture professionals on safety matter.
 
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Online Aldo22

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Re: Has anyone ever megged a multimeter ? (HV testing)
« Reply #37 on: January 25, 2025, 08:45:35 am »
Is Dave the gold standard for all advice?

Yes, of course!  ;D

No, but what he writes here sounds sensible, balanced and comprehensible.
I'm sure the professionals here actually know that, but don't admit it for various, probably well-intentioned reasons.
« Last Edit: January 25, 2025, 10:29:17 am by Aldo22 »
 

Online tggzzz

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Re: Has anyone ever megged a multimeter ? (HV testing)
« Reply #38 on: January 25, 2025, 09:46:11 am »
Is Dave the gold standard for all advice?

Yes, of course!  ;D

No, but what he writes here sounds sensible, balanced and comprehensible.
I'm sure the professionals here actually know that, but don't admit it for various reasons.

Sounding that way is completely insufficient.

As tautech pointed out, the published standards are the appropriate source.

One characteristic of such standards and codes of practice is that they often contain sections that appear bizarre and/or irrelevant. That's because they reflect what has been a subtle and/or rare problem in the past. They appear bizarre/irrelevant because the reader doesn't know/imagine/understand the problem. Another classic example of that phenomenon is disconnecting protective mains earth when floating a scope.

It is reasonable and acceptable to be ignorant of the reasons standards/codes are the the way they are. It is not acceptable to push the line that the standards are unnecessary in some way.
There are lies, damned lies, statistics - and ADC/DAC specs.
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Offline pryce64

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Re: Has anyone ever megged a multimeter ? (HV testing)
« Reply #39 on: January 25, 2025, 12:39:09 pm »
Afternoon,
Not sure why you would megger a DMM.
Part of my role is we megger electronic equipment used in rail traction equipment.
You first megger between vehicle earth and battery +ve and -ve record readings, then you apply high voltage flash test then you re megger.

I have seen a AVO 8 meter blown to bits by sticking it across to high of a voltage and the noise was impressive.

Built megger and flash ATE system to check RS485 cable on Class 390 tilt trains, no train was harmed.
 

Offline tautech

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Re: Has anyone ever megged a multimeter ? (HV testing)
« Reply #40 on: January 25, 2025, 01:40:43 pm »
Afternoon,
Not sure why you would megger a DMM.
Part of my role is we megger electronic equipment used in rail traction equipment.
You first megger between vehicle earth and battery +ve and -ve record readings, then you apply high voltage flash test then you re megger.

I have seen a AVO 8 meter blown to bits by sticking it across to high of a voltage and the noise was impressive.

Built megger and flash ATE system to check RS485 cable on Class 390 tilt trains, no train was harmed.
How high ?

AVO's typically had 2.5 or 3kV max ranges and were subject to a standard 7kV flashover test.
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Offline m k

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Re: Has anyone ever megged a multimeter ? (HV testing)
« Reply #41 on: January 25, 2025, 02:11:11 pm »
It would be interesting to see an accredited lab run independent tests on meters

I've not seen it, but I've seen results after mains connected electronics testing.

Back in the day the machine was burned if it didn't include an accepted report of used materials and their smoke properties.
With accepted report it was still partially burned using overvoltage to see how it ignites.
In case the machine included safety features, like preventing overloading, all of those features were bypassed and tested again.
If memory serves the minimal amount needed was three machines.

The entity behind those tests was the old "FI" approval sign ratifier, like "S", "N" and "D" for other nordics.
Compared to "CE" those old signs were real approvals.
Advance-Aneng-Appa-AVO-Beckman-Danbridge-Data Tech-Fluke-General Radio-H. W. Sullivan-Heathkit-HP-Kaise-Kyoritsu-Leeds & Northrup-Mastech-OR-X-REO-Simpson-Sinclair-Tektronix-Tokyo Rikosha-Topward-Triplett-Tritron-YFE
(plus lesser brands from the work shop of the world)
 

Offline pryce64

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Re: Has anyone ever megged a multimeter ? (HV testing)
« Reply #42 on: January 25, 2025, 04:26:03 pm »
How high,

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

Online bdunham7

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Re: Has anyone ever megged a multimeter ? (HV testing)
« Reply #43 on: January 25, 2025, 04:40:26 pm »
It is not acceptable to push the line that the standards are unnecessary in some way.

Why?  Is there some public policy restriction on what we're allowed to say?  I see no issues with simply pointing out that arc-flash is not a household hazard.
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 
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Offline pryce64

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Re: Has anyone ever megged a multimeter ? (HV testing)
« Reply #44 on: January 25, 2025, 05:17:19 pm »
Disagree,

Arc-flash is a household hazard, to the hobby welder as me and our Niel found out while trying to weld a FIAT 500 floor pan in without using a shield back in 1980 and ending up in A&E(hospital).
 
 

Online joeqsmith

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Re: Has anyone ever megged a multimeter ? (HV testing)
« Reply #45 on: January 25, 2025, 05:29:14 pm »
It is not acceptable to push the line that the standards are unnecessary in some way.

Why?  Is there some public policy restriction on what we're allowed to say?  I see no issues with simply pointing out that arc-flash is not a household hazard.

Just to be clear, I could care less about surge or fault currents when working at home. 

Multimeter safety is a tad overrated, and has been pushed toward the extreme end of the OH&S spectrum.
That's not a bad thing of course, in fact it's great, but people do get a tad carried away.
Sure the general recommendation of "CAT III for anything mains related and above" is good general advice, but it's not needed.
Most people do not work on such high energy systems to warrant being that worried about it.
And basically it's limited to only one fault scenario, probes in the A jack by mistake when measuring mains or another high energy system.

The above suggests that people who do work in industrial environments only need to be concerned with placing the leads into the Amps jacks and measuring current. 

The whole peak overload thing (e.g lighting strike on the mains) is so remote an issue that it's almost not a thing.

The above suggests that in an industrial environment, the only source of high energy over loads is lightning.  While I am not an electrician and do not work in a factory, even my limited exposure to what goes on around the world suggests both statements are false.   

When I wrote:
Quote
I have seen some meters that will breakdown during my testing or supplied with glass fuses.  For these special meters, I will apply the HV transient (enough to cause the meter to arc and develop a low impedance path) and then inject enough energy to simulate a half cycle of AC (about 600J max).   Not a lot, but enough to provide some idea of what could happen.

I suspect that low voltage transient generator I designed could be applied directly to ANY handheld DMM I have evaluated, and nothing would happen.   The reason is the voltage it puts out is so low, it is within the working range of products I have looked at.    The damage comes from a meter that breaks down, or arcs.   The low impedance path basically shorts the low voltage generator.   It doesn't take a lot of energy to get a meter to break down.  I test at less that 20J.

Point being that we really don't even need a high energy, high voltage transient to start such a reaction.   Any transient that caused a DMM to arc is good enough. 

While I harp on people who claim my testing is about safety, it is hard to ignore that if you have a meter that breaks down at low voltages, it could present a problem.  Again, not at home, or at least my home.   Again, look at that fault current data I provided for my lab.   But in an industrial environment where arc flash is possible, I personally wouldn't use such a meter.    Sound like Dave along with a few others, see it different.   

Online joeqsmith

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Re: Has anyone ever megged a multimeter ? (HV testing)
« Reply #46 on: January 25, 2025, 05:36:14 pm »
Disagree,

Arc-flash is a household hazard, to the hobby welder as me and our Niel found out while trying to weld a FIAT 500 floor pan in without using a shield back in 1980 and ending up in A&E(hospital).

I am interested in details about what happened in your specific case?

Online tggzzz

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Re: Has anyone ever megged a multimeter ? (HV testing)
« Reply #47 on: January 25, 2025, 05:44:46 pm »
It is not acceptable to push the line that the standards are unnecessary in some way.

Why?  Is there some public policy restriction on what we're allowed to say?  I see no issues with simply pointing out that arc-flash is not a household hazard.

Is there a "public policy restriction" on telling inexperienced people that it is OK to run or walk into a road without looking? Would anybody regard it as acceptable to tell a child that?

It must be OK, since I've walked into a road without looking and haven't come to any harm (yet).
There are lies, damned lies, statistics - and ADC/DAC specs.
Glider pilot's aphorism: "there is no substitute for span". Retort: "There is a substitute: skill+imagination. But you can buy span".
Having fun doing more, with less
 

Online bdunham7

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Re: Has anyone ever megged a multimeter ? (HV testing)
« Reply #48 on: January 25, 2025, 05:46:02 pm »
Disagree,

Arc-flash is a household hazard, to the hobby welder as me and our Niel found out while trying to weld a FIAT 500 floor pan in without using a shield back in 1980 and ending up in A&E(hospital).

Perhaps that term means something different to you than it does to me. 

https://en.wikipedia.org/wiki/Arc_flash

A welding suntan (or burn) is a different occasion, although arguably due to similar causes.

A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Online joeqsmith

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Re: Has anyone ever megged a multimeter ? (HV testing)
« Reply #49 on: January 25, 2025, 05:55:08 pm »
Disagree,

Arc-flash is a household hazard, to the hobby welder as me and our Niel found out while trying to weld a FIAT 500 floor pan in without using a shield back in 1980 and ending up in A&E(hospital).

Perhaps that term means something different to you than it does to me. 

https://en.wikipedia.org/wiki/Arc_flash

A welding suntan (or burn) is a different occasion, although arguably due to similar causes.

So you think he is suggesting that the arc as a result from welding and a bit of sun burn is what he is referring to as an arc flash?  It could be.  The arc blast from it would do much.  At least, I have never felt any sort of pressure wave while welding.


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