Has anyone ever megged a multimeter ? (HV testing)

[LinuxGuy123]

There is lots of talk about how some (less expensive, imported) multimeters are or could be dangerous for HV work.

Has anyone ever connected a (cheap) multimeter to a HV source and tested its rating or purposely destroyed one ?

[Kean]

Oh boy, you have some catching up to do...

https://www.eevblog.com/forum/testgear/hear-kitty-kitty-kitty-nope-not-that-kind-of-cat/

https://www.youtube.com/@joesmith-je3tq/videos

[LinuxGuy123]

This group never disappoints !   Excellent work.

[joeqsmith]

Kean became an unintentional expert in this area 

https://www.eevblog.com/forum/testgear/hear-kitty-kitty-kitty-nope-not-that-kind-of-cat/msg1601299/#msg1601299

[Kean]

Good memory Joe!

Gee, that was 6.5 years ago and I've not yet managed to repeat it.  I've actually been fixing things quicker than damaging them lately  .

[bdunham7]

Has anyone ever connected a (cheap) multimeter to a HV source and tested its rating or purposely destroyed one ?

Blowing up meters is a common sport around here.  Dave Jones posted a video long ago blowing them up (literally) with a huge capacitor bank.

The problem with just using a Megger or low-energy HV source is that it isn't really testing what meters are most vulnerable to in real life, namely transients and high energy circuits.  In fact, using a Megger or HVDC, the cheapest or most unprotected meters may actually outperform good meters because they don't have any devices that clamp overvoltages.

I've attached a photo of is what is widely regarded as the worst of the worst cheap meters--although it theoretically has an infinite bang-for-buck ratio because the typical price was $0.00 at Harbor Freight.  As you can see, the meter is rated for 250VAC but I have it connected to 1100VAC and other than being not very accurate, it doesn't fail in any way.  I don't have my HV supplies set up on bench right now, but I previously connected a different version (the older, yellow ones that had 1000VAC/750VAC printed on them) and I was able to crank it up to 1600VDC and it just indicated the voltage without complaint.  I would have gone to 2000 volts but the input divider was smoking a bit so I backed off.  They only have a 1M input impedance so at 1600V that miniscule resistor is dissipating over 2.5W.

A CAT-III/600V meter might be better and safer in every way but not do as well with those inputs because the input devices would start to clamp and dissipate heat.  They're designed to withstand transients at much higher voltages but not necessarily continuous application of severe overvoltages.  Good meters will also withstand full rated input voltage even if you select the wrong range, perhaps ohms, temperature or capacitance.  There is a video somewhere of a Fluke rep demonstrating this using the very same HF meter that I have here. For home electrical in North America even this cheap Harbor Freight meter is unlikely to be the primary cause of any serious injuries even if used in service panels or outdoor wiring because single-phase 240VAC just doesn't pose the same hazards that three-phase high-energy installations do.  If it blows up because you left it in ohms mode while testing your circuit breakers  or left the leads in the amp jacks, you'll just get minor burns and flying shrapnel at the worst--maybe bit of molten metal in the eye.  I would be more concerned about the atrocious leads and semi-sheathed connections than anything else. 

[Aldo22]

... even this cheap Harbor Freight meter is unlikely to be the primary cause of any serious injuries even if used in service panels or outdoor wiring because single-phase 240VAC just doesn't pose the same hazards that three-phase high-energy installations do.  If it blows up because you left it in ohms mode while testing your circuit breakers  or left the leads in the amp jacks, you'll just get minor burns and flying shrapnel at the worst--maybe bit of molten metal in the eye.  I would be more concerned about the atrocious leads and semi-sheathed connections than anything else. 

Exactly! 
And with a ZT-225, not even that happens.
The sturdy structure alone with the fat, slightly elastic holster simply does not allow it to “blow to smithereens” (attachment).
It is immune to incorrect setting of the selector.
The only place where something could happen is the 20A input with ceramic fuse.
But the circuit breakers are at 16A in our house. What comes first?

Nevertheless, “cheap” DMMs are always eagerly discouraged here because they said to be “unsafe” and potentially deadly.
Deadly for whom? For Fluke? I don't think so. 

And before you get into anything that requires electrician training, you should get electrician training.
Then you'll know what tools and safety measures you need. That might not include a Zotek meter, but protective goggles, protective gloves, a second person...

But for anything on this side of CAT II, I wonder what the point of these exaggerated warnings is?
After all, this is an "electronics engineering" forum and not a lineman forum. 

[Zero999]

Insulation testers apply a tiny current, typically around 1mA, which shouldn't damage a decent multimeter.

[joeqsmith]

I look for meters that are electrically robust and care little about safety.  Cost doesn't seem to be a factor as the $50 Fluke 101 was one of the most robust meters I have looked at to date.  I personally want a meter that can survive some basic low level transients because I do experiment with electronics beyond the world of logic gates and ESD is a factor in my home.   

At least at my home, arc flash is of no concern.  Someone once brought up fault currents and I took the time to measure them in my lab.   
https://www.eevblog.com/forum/testgear/trashy-meters-redux/msg4835948/#msg4835948

Insulation testers apply a tiny current, typically around 1mA, which shouldn't damage a decent multimeter.

I had seen a few videos of people running such a test, claiming they were putting some high voltage across the meter but ignorant of the fact that the meter was loading down the supply.  Viewers comment how great the meters are for surviving such a high voltage.   

My question is why does the vintage Fluke calibrator need such bling?   My wife fixed up my whore of a scope.   Maybe some nice hoop rings and gold chain would have augmented the look. 

[bdunham7]

It is immune to incorrect setting of the selector.

And before you get into anything that requires electrician training, you should get electrician training.

After all, this is an "electronics engineering" forum and not a lineman forum. 

I'm not going to sneak into your house at night and confiscate your meter, but I have some issues with those three statements.

First, IIRC there is a Youtuber who tested the meter in ohms, etc at 220VAC.  The meter is labeled, among other things, as "CATIII/1000V".  Just to prove a point I put my old Fluke 27 in ohms mode and applied 1000VAC, photo attached.  No harm done, meter is still fine.  IDK, maybe your ZT-225 would do as well--or perhaps not.  Would you try it?  It's not just an explosion or fire issue, it's also a question of whether the meter is easily killed or not.

Next, the "you shouldn't be doing that anyway" argument doesn't address the issue of whether a device meets the ratings that are printed on it.  The OP clearly works with systems that have significant energy and didn't seem to be aware that some meters that are labeled as appropriate for that might not actually be up to the task.  Some people would look at my old Fluke 27 which is labeled only CAT III/1000V and compare it with the newer ZT-225, which is additionally labeled CAT IV/600V, and then conclude that the newer meter with the additional rating is probably better.  Zotek's own marketing repeatedly mentions the CAT ratings and claims it is an appropriate tool for "electricians and maintenancers".  I'm not convinced.

https://zotektools.com/products/zoyi-zt-225/

[bdunham7]

My question is why does the vintage Fluke calibrator need such bling?   

The calibrator is standing up and since the face is now a horizontal surface, it accumulates stuff.  That's a Timex watch that I'm suppose to fix someday.

[joeqsmith]

If you place a second meter in parallel with the Fluke, do you actually get 1000VAC out of the calibrator?   When you let the Fluke cool, then turn on the calibrators output, does it immediately read 1kV?  I'm surprised it can drive that much current.

[tooki]

If you place a second meter in parallel with the Fluke, do you actually get 1000VAC out of the calibrator?   When you let the Fluke cool, then turn on the calibrators output, does it immediately read 1kV?  I'm surprised it can drive that much current.

The datasheet says 6mA maximum.

[Fungus]

And with a ZT-225, not even that happens.
The sturdy structure alone with the fat, slightly elastic holster simply does not allow it to “blow to smithereens” (attachment).
It is immune to incorrect setting of the selector.
The only place where something could happen is the 20A input with ceramic fuse.

Go watch a few more joesmith videos. There's quite a few where the meters jump around inside the box even on his low energy generator.

Converting copper into vapor is an explosive process.

Even if it doesn't kill you directly the fright of it going "bang" in your hand could easily make you fall off a ladder or something.

[Aldo22]

I'm not going to sneak into your house at night and confiscate your meter,

You are welcome! 
Second option: Order one just to see what it can take.
https://www.aliexpress.com/item/1005007244323221.html

First, IIRC there is a Youtuber who tested the meter in ohms, etc at 220VAC.  The meter is labeled, among other things, as "CATIII/1000V".  Just to prove a point I put my old Fluke 27 in ohms mode and applied 1000VAC, photo attached.  No harm done, meter is still fine.  IDK, maybe your ZT-225 would do as well--or perhaps not.  Would you try it?  It's not just an explosion or fire issue, it's also a question of whether the meter is easily killed or not.

I don't have a 1000V source myself, and to be honest, I'm about as interested in that as whether the DMM implodes at the bottom of the Mariana Trench.
And with a DMM that costs as much as a Fluke fuse, I'm not interested in whether the DMM will break in (for me) unrealistic situations.

Next, the "you shouldn't be doing that anyway" argument doesn't address the issue of whether a device meets the ratings that are printed on it.  The OP clearly works with systems that have significant energy and didn't seem to be aware that some meters that are labeled as appropriate for that might not actually be up to the task. 

Yes, but he OP also said in the other thread that he will continue to use his Agilent 1271A for the “dangerous stuff”.
I also pointed out there that I would use a more professional tool than the Zoyi for his case (480VAC).
Not necessarily because I think the Zoyi would kill him, but simply because I assume a different attitude to safety-related issues in these areas.


But that's not really my point at all.
Why don't you just say, “The ZT-225 is an incredibly great DMM for electronics hobbyists at a very reasonable price.
If you think the meter might fall into the wrong hands, scrape out the CAT ratings and have fun measuring microvolts and nanoamps." 

[tooki]

And with a ZT-225, not even that happens.
The sturdy structure alone with the fat, slightly elastic holster simply does not allow it to “blow to smithereens” (attachment).
It is immune to incorrect setting of the selector.
The only place where something could happen is the 20A input with ceramic fuse.

Go watch a few more joesmith videos. There's quite a few where the meters jump around inside the box even on his low energy generator.

Converting copper into vapor is an explosive process.

Indeed.

Someone made a video about this very topic the other day:



One nugget of info from it: in nuclear bombs, they don’t use chemical igniters to start the reaction because the timing is too imprecise. So they use exploding wire to time it to ns precision. It’s not the thermal effects, but the actual pressure wave from the exploding wire that is used to begin the explosions that ultimately compress the fissile material to criticality.



Our resident multimeter anti-safety crusader, Aldo22, is absolutely correct that most people here do not need a meter capable of protecting users from high-energy discharges, since most forum users aren’t working on high-energy circuits. But I do think he wildly underestimates what high-energy circuits are capable of, and may not fully understand which circuits are actually high-energy enough to be problematic.

[Aldo22]

Some people would look at my old Fluke 27 which is labeled only CAT III/1000V and compare it with the newer ZT-225, which is additionally labeled CAT IV/600V, and then conclude that the newer meter with the additional rating is probably better.  Zotek's own marketing repeatedly mentions the CAT ratings and claims it is an appropriate tool for "electricians and maintenancers".  I'm not convinced.

In my case, I wouldn't need these CAT ratings on the Zoyi and perhaps it would be clearer to simply leave them out. You're right about that.
It would still be the same useful device for me and we wouldn't have to have these irrelevant discussions all the time.

[themadhippy]

If your gonna use a megger then at least use a megger thumper not a piddle little 1000v megger insulation tester

[bdunham7]

If you place a second meter in parallel with the Fluke, do you actually get 1000VAC out of the calibrator?   When you let the Fluke cool, then turn on the calibrators output, does it immediately read 1kV?  I'm surprised it can drive that much current.

Yes and no.

I don't need actually need the parallel meter as the calibrator will shut off if it is overloaded and can't maintain the voltage.  It's pretty good about that--it will display OL pretty quickly anytime the feedback loop isn't satisfied and then shut off the output if that continues for more than a few seconds. 

For initial output into a cold PTC it indeed cannot put out the 250mA or so that would take so I have to "walk it up" by heating the PTC in stages.  I'll start at 200VAC and then turn it up over a 15-20 second period.  I do have DC supplies that will put out enough of a surge that they can drive the meter directly at 1000VDC but they're not connected and ready right now.  The result is the same, as one would expect.  The clamps just have to be big enough to not blow up (or off the board) and the Fluke 27 uses "select" MPS6560 or similar transistors in a TO-92 case. 

[bdunham7]

Yes, but he OP also said in the other thread that he will continue to use his Agilent 1271A for the “dangerous stuff”.

Yes, he did say that after the issue was pointed out.

But that's not really my point at all.
Why don't you just say, “The ZT-225 is an incredibly great DMM for electronics hobbyists at a very reasonable price.
If you think the meter might fall into the wrong hands, scrape out the CAT ratings and have fun measuring microvolts and nanoamps." 

Well I don't say it because that's your point.  And if the meter wasn't labeled or said "not for electricians" or something like that, I'd have no objections.  I do have meters and stuff on my bench that probably aren't protected any better than the ZT-225 but I do prefer stuff that doesn't blow up if I make a mistake.  Bench PSUs that blow up if you connect a battery to them are my other pet peeve....

[tooki]

Some people would look at my old Fluke 27 which is labeled only CAT III/1000V and compare it with the newer ZT-225, which is additionally labeled CAT IV/600V, and then conclude that the newer meter with the additional rating is probably better.  Zotek's own marketing repeatedly mentions the CAT ratings and claims it is an appropriate tool for "electricians and maintenancers".  I'm not convinced.

In my case, I wouldn't need these CAT ratings on the Zoyi and perhaps it would be clearer to simply leave them out. You're right about that.
It would still be the same useful device for me and we wouldn't have to have these irrelevant discussions all the time.

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.

[joeqsmith]

Converting copper into vapor is an explosive process.

Correct and was the basis for my model rocket. 

[Aldo22]

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.
I don't know enough about it.

But yes, as Dave Jones said, the CAT I and II declarations on the front of a meter will be removed in future anyway. That would be a good opportunity to do away with dubious CAT ratings completely.

Personally, I am interested in other things, such as accuracy and precision/resolution, measuring range etc. etc.
I have never bought a DMM because of CAT ratings.

[joeqsmith]

...
 I do have DC supplies that will put out enough of a surge that they can drive the meter directly at 1000VDC but they're not connected and ready right now.  The result is the same, as one would expect.  The clamps just have to be big enough to not blow up (or off the board) and the Fluke 27 uses "select" MPS6560 or similar transistors in a TO-92 case. 

I will test them with DC based on what ever they claim the meter can handle (normally 600 or 1kV).  But I only do this with the meter set to DCV and I slowly bring them up.  To date, this has never cause any meter to fail.  No surprise. 

The homemade transient generator does have a 220V transformer which I run through a full wave rectifier and apply to the meter with them set to each mode.   The transient generator measures the current through the meter and will turn off if it gets too high.  The only time it trips is when I have demonstrated this circuit by shorting the output or driving something like an incandescent bulb as a load.   This simple test has damaged six meters to date.

I also perform a 1kV transient test.  I would expect every meter would pass this but  six of them have failed.  They don't like that fast edge.   I have a kV supply that can easily output enough current that it will not droop when driving a meter, but I don't use it as part of my testing.  My guess based on the 1kV transient tests, there are meters out there it would damage. 

As a hobbyist, and a cheap one at that, I am also interested in if I can repair the meters after they are damaged.  Someone recently posted how I am able to repair the majority of them.  Actually, the majority are damaged beyond repair.   Some, like that crappy, expensive Keysight use custom parts that are not protected.  Once damaged, good luck finding parts.   Many of the < $100 use COB which are often damaged. 

IMO, the worse meters are the ones that cost >$20 that can't survive a basic ESD pulse.   The free meters from HF will not survive much of anything but they are free with purchase.  They are on par with my first Fluke meter.

[joeqsmith]

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.

For home use, same.  I could care less about 61000 safety.  I want something that survive 61326.   The accuracy, ..... other specs, I have to trust the manufacture to meet what they claim as I have no way to test them for calibration.   Still, I don't recall seeing any meters that appeared to be far out of spec when I do my basic checks.