Do cheap meters explode when you abuse them?

[george graves]

See Martin's video of his visit to Fluke.

http://mjlorton.com/forum/index.php?topic=821.0

It is a good video to watch to learn about fluke testing - kinda - there's a lot of sales pitch thrown in - but they guy makes a great show of why flukes are safe to probe +300v.  Mjlorton's videos are often full of flaws. (Like tons of them)  He openly admits it in his show opening, that he's just mucking about.  Take anything he says with a grain of salt. 

[paulie]

Paulie keep arguing until someone gets hurt,

I probably will not follow your advice as suggestions like that are indication of a twisted personality. You do seem to be a perfect example of the type alluded to earlier so forgive me if I take your claim of seeing "a multimeter and leads blow up in person" with a grain of salt. "Shock" tactics don't work on me.

Anyway there is more news on cheap meters vs protection. All the whining about having to spend a hundred bucks or even as little as fifty to save lives may be a bit misplaced in view of recent dissection of my $12 Uni-T meter (well, I took the back off) . Turns out to my surprise there IS a 10a fuse in addition to the milliamp one. And guess what? CERAMIC !!! I know some of us love those.  Let's think up some other picayune trait for those with more money than brains to go on and on about.

ps. I can put up some photos if there is interest.

[Kleinstein]

For the Uni-T meters, there are several versions, that look very similar from the outside and have same label.  So especially with a very cheap meter, unless you open it up, you don't know if you get the version for US, European (possibly OK) or the Chinese / Russian marked or even a countrified one thats even worse. So even if one meter survives a test this does not mean that model is safe. At best a failed test shows that this model is not safe.

With mains voltage, the distance to the meter and transformer can make a big difference. I once saw what happens if distances are short (in this case very short - less than 5 m to the distribution transformer). A normal ligh bulb blew with an short - normaly just the fuse blows. However this time the 16 A (electromechanical) and 35 A (melt type) and 100 A fuse blew. The light bulb literally exploded with the glass partially covered with copper from the inside. The cable to the fuse cabinet and from fuse cabinet turned brown.  Likely the 16 A fuse was not able to brake the current - though rated at something like 6 to 10 kA. So be extra careful if you have a low impedance output that might need CAT III rating.

[Fungus]

my $12 Uni-T meter (well, I took the back off) . Turns out to my surprise there IS a 10a fuse in addition to the milliamp one. And guess what? CERAMIC !!!

Sure. In yours.

PS: That statement should tell you something about yet another difference between Uni-T and Fluke.

[SeanB]

You get fake ceramic fuses as well, I have had them explode in microwave ovens before, where they are supposed to blow without turning into shrapnel.

[nanofrog]

You get fake ceramic fuses as well, I have had them explode in microwave ovens before, where they are supposed to blow without turning into shrapnel.

Sadly, if there's a profit to be made as a result of producing counterfeits, someone will.

[Lightages]

Let's think up some other picayune trait for those with more money than brains to go on and on about.

Hmmmmm, I wonder which is worse, being liberal with other people's money, or being liberal with other people's safety?

It can be, and has been demonstrated that cheap meters have injured and killed people. I am sure you cannot demonstrate the opposite.

And why are you insulting other people here instead of sticking to the subject? This is usually a sign that a person does not have valid points or real evidence to back their claims.

[helius]

ceramic fuses are not the highest safety rated kind of fuse. ceramic is a brittle material and will shatter with sufficient force. the HRC fuses are made from woven melamine for this reason.

[johansen]

If you need to hold the meter in your hand while probing fused mains circuits, then you should get a professional quality, appropriately rated one with a rubber sleeve on it as that adds extra protection where you are most likely to be gripping it, which can only help if it fails catastrophically.   If you are probing high current high voltage circuits, you should be using individually fused test leads as well.

make sure to wear a face shield 

[John Coloccia]

Personally, I think we should stop arguing and simply let evolution run it's course.

[helius]

If you are probing high current high voltage circuits, you should be using individually fused test leads as well.

I have a question about this. Do both leads need to be fused? If only one, does it matter if it is the high or low side (or the + or common jack?)

[nanofrog]

ceramic fuses are not the highest safety rated kind of fuse. ceramic is a brittle material and will shatter with sufficient force. the HRC fuses are made from woven melamine for this reason.

I've Cooper-Busmann's that have the woven body you describe, but the Siba's I have, use a smooth, unglazed porcelain/ceramic type of finish (may not actually be a ceramic type of material, just the best description I can give).

FWIW, I do have a blown Siba sitting around I kept for the P/N, just never bothered to tear it apart (P/N = 5019906.11). Maybe time to break out the Dremel... 

[retiredcaps]

I've Cooper-Busmann's that have the woven body you describe, but the Siba's I have, use a smooth, unglazed porcelain/ceramic type of finish (may not actually be a ceramic type of material, just the best description I can give).

Modemhead had pictures of his Cooper Bussmann fuse.  If I remember the story correctly, he forgot to change back the probes back to the appropriate input jacks while measuring mains?

http://mrmodemhead.com/blog/inside-a-multimeter-fuse/

[Ian.M]

If you are probing high current high voltage circuits, you should be using individually fused test leads as well.

I have a question about this. Do both leads need to be fused? If only one, does it matter if it is the high or low side (or the + or common jack?)

Both.  Otherwise you cannot safely make a phase to phase measurement.

The fuses are for protection if the leads get damaged, and if an unfused lead clipped to  neutral or earth drags across a sharp edge on a live terminal, you are going to get arc flash.  At best, with the right PPE it will ruin your week, at worst, it would be preferable if it actually kills you outright.

[Muxr]

Fear the arc flash:

[joeqsmith]

I have been reading 61010-2-033:2012.   

Part 2-033: Particular requirements for HAND-HELD MULTIMETERS
and other METERS, for domestic and professional use,
capable of measuring MAINS voltage

I assume this is what they mean when they test to when the refer to 1010.     It is very interesting.       


Setup a simple experiment to create the 8/20 waveform.   I did not have the parts needed, but came up with something more like an 4/8, up to 4KV.  Only makes about 500A with a 2 ohm source.   Really not talking about a lot of energy.    I didn't want to get too crazy with it, so left off the mains and just hit the BK with the spike alone to see if the meter would handle it.   I assume if the generator is on a 50A service, with 220 mains,  all hell's going to break loose if the meter has any sort of internal breakdown.   

So I started out just using 2KV with the meter in DC volts.  Meter is CAT II.   Wasn't expecting much with such a short pulse and low voltage.    Picture shows damage after one hit in the positive direction.  Sorry, I did not make a video of it.

Would have been fun to see what would have happened on a real setup. 

This meter was marked CAT II.   I expected it to take handle this little test with ease.   Really curious now about other meters.    After this experiment, if I actually ever needed to check something on a CAT III or IV setup, I would need to see the mfg's test report before I would even consider it..   Then I would take out an insurance policy....    There is no way I would just trust any meter, even if it has a lot of marks on it and it costs X that it would not flash over. 

So explode when abused, sure. 

[paulie]

Looks like "explode" is in the eye of the beholder. When the dial from Dave's Fluke blows off across the room everything is "good as gold" even though obviously destroyed by the blast. But no explosion here. A chip with pit or black mark on the PCB definitely cause to call the bomb squad. This does seem to be one of the more entertaining threads to come along in a while. Not so much technical but more a study in human psychology.

[joeqsmith]

"burst or shatter violently and noisily as a result of rapid combustion, decomposition, excessive internal pressure, or other process, typically scattering fragments widely."

Yea, an explosion....  just not on an epic scale.  Again, the real energy is from the mains after the flash over.   Because there were no mains involved, the explosion was minimized.    Sorry, there is no way I would consider attempting a scaled down lines test.    I am not setup for it.   

Dang, I was way off on my post.....  Here is the waveform that exploded the BK on an ant scale   

C1, is looking at current with a Pearson current transformer.  The scale is 0.1 volts per Amp or 200 Amps/div.    C2 is using one of my new homemade 100X probes.  1KV/div  Rise time is really maybe 3nS ad 200nS width.    Imagine a real test setup....   



 

[paulie]

"burst or shatter violently and noisily as a result of rapid combustion, decomposition, excessive internal pressure, or other process, typically scattering fragments widely."

Sorry but from my viewpoint it was more like "one fragment scattered closely" rather than "fragments scattered widely". Some of the videos posted did show what I consider explosions but unless at the least case flies apart no explosion. Only harm would come to those inside the case.

I am interested in better description though. Not sure what BK is and was that 2 kilovolts at 500 amps? If so we have different idea of what's "not talking about a lot of energy".

So with previous mention of scope and cfl supplies it looks like I will have to reproduce my kv geiger accidents except on purpose this time and document. My HF meter worked fine afterwards but we were talking microamps not amps. Stay tuned.

[joeqsmith]

I am interested in better description though. Not sure what BK is and was that 2 kilovolts at 500 amps? If so we have different idea of what's "not talking about a lot of energy".

Well, you could start by reading the standards they test to.     

Think in terms of Joules, not Watts.   Time.   So again, the duration is very short compared to what the standards call for (<< Joules).   Now again consider that once that energy dissipates, that's it.   If there were an infinite supply of energy (AKA the power lines) that could continue to feed the fire, we get some scary things happening.   

So, say it was a square pulse I hit it with (obviously it was not).  Power = VI or 2KV *500A or 1MW.  You think, WOW that's a lot of free energy!  But we need to consider it was only there for 200ns.   Energy = Power * Time. 

With the line sure we may only have a few hundred volts and much lower currents, but time is much much much larger..      While the device we tested may have required a small amount of energy at a few KV to start the reaction,  it only needs a very small voltage to sustain it.   Think about how a TIG welder works. 

Hope this helps clear up the difference between power and energy.   

[dom0]

The impulse in the scope shot above has about ~40 mJ ... that's like, nothing, but still enough to blow the chip and destroy the meter.

[paulie]

You're a prime candidate for Narcissistic Personality Disorder. Don't listen to anyone, shoot down all advice, preoccupied with your own agenda, endangering others while you do it. Anyone who has been around the block a few times spots idiots like you a mile away, sorry about that, you might not like hearing it,

Are you kidding me? I LOVE hearing this stuff. Getting guys like you going is one of the main reasons to keep coming back here. Hooking borderline personalities is every trolls dream. Actually it's better than just trolling for me... more like shooting the fish in a barrel.... no tackle or lines required. LOL

I never initiate personal attacks. Ever. But when dudes like you and Lightage start I do enjoy playing. Please continue. But I do think you can do better than that. Maybe slightly less lame next time.

[paulie]

Well, you could start by reading the standards they test to.

Unfortunately I can't do that. If caught I could lose membership in the anti-safety league.

All seriousness aside, I am more interested in the actual meter you used and the equipment for the test. Obviously more of a science experiment and not something the average arduinotard hobbyist would encounter but still interesting. Kinda like the equipment in that Fluke "public service" video ( http://mjlorton.com/forum/index.php?topic=821.0 ). Maybe a photo or at least more info on that meter and test setup.

[Fungus]

You're a prime candidate for Narcissistic Personality Disorder. Don't listen to anyone, shoot down all advice, preoccupied with your own agenda, endangering others while you do it. Anyone who has been around the block a few times spots idiots like you a mile away, sorry about that, you might not like hearing it,

Are you kidding me? I LOVE hearing this stuff. Getting guys like you going is one of the main reasons to keep coming back here.

You think you're a maverick but really you're just a redneck and all you're 'constructing' is this:

The only reason anybody's bothering with you is you haven't figured out that hundreds of newbies might be reading extracts of this via google results and thinking there's no difference between a $4 multimeter and a $40 Fluke.

[paulie]

Yeeeee... Hawwwww !!! The more fish in that barrel the merrier. Specially such fine members of the community defending truth and justice (if not American Way) from troglodytes like me. gnawww... gnawwww... LOL

And BTW I do know the difference. Exactly $36 USD. And with some element of "Lamborghini Syndrome" and touch of FUD.