Multimeter mistakes

[musht]

Certainly made me think about where would stick the probes of a low cost meter

 

http://ecmweb.com/ops_maintenance/defectiv...pment-20100101/

[dbuckley]

I had a low cost analogue Maplin meter go bang on me many years ago measuring across 415V. Despite the fact it was nothing like the incident reported above, I did need a change of underwear.

 

On returning the meter to Malins, they claimed I must have been changing ranges whilst the probes were connected.

 

That one incident has marred my opinion of Maplins ever since.

 

Now I wouldn't go near power electrics with a meter that wasn't Cat III certified for above the voltage concerned.

 

Arc flash is a really scary thing. If you think you're up to it (ie watching people dying), go search youtube.

[Smiffy]

Fluke... They really should be considered the ONLY people that make mains test equipment I've had my meter for years, never an issue with it. Although it rarely leaves the house these days as I tend to spend most of my time behind the production desk rather than knee deep in the kit...

 

 

Edit: SpAG

[KevinE]

Fluke... They really should be considered the ONLY people that make mains test equipment

 

Bit misleading, this! There are many brands of suitable equipment.

[Smiffy]

Old habits die hard Kevin :** laughs out loud **:

[dbuckley]

Fluke... They really should be considered the ONLY people that make mains test equipment

Bit misleading, this! There are many brands of suitable equipment.

There indeed are, and I have several, but there is the old truism: "In Fluke we trust".

 

Thus if you dont know any better, and to bend an old saying, you wont get fired for buying Fluke.

[Robin Pratt]

I sort of argree with Smiffy here in that I wouldn't risk using an own brand or "budget" test instrument for live mains work, but there are reputable brands other than Fluke that I'd be happy with. I'm quite happy with mains test gear from all the big names like AVO/Megger, Martindale, and being me of course, Robin :** laughs out loud **:

 

Of course its equally important not to use damaged probes or leads, and only to use the proper spec. fuses in them.

[JimWebber]

Ouch!!!

 

I will never forget a (near) incident a couple of years back.

 

I was training about four students in a certain electrical system. I am not joking when I say I cannot go into details here, but let us just say that it is on the complicated side. We were discussing the operation of one of the cabinets, and one of the students asked me what the output voltage of a certain transformer was.

 

In true facilitive style, I said "Find it out for yourself" and handed him a (Calibrated and tested) Fluke.

 

I should at this point say that I was dealing with a mature, experienced engineer with plenty of previous experience.

 

He then took that meter, and in a moment of madness, set it to "A" and approached the transformer terminals with the test probes. The look on his face when I bawled at him, and knocked it out of his hands was a picture. Once I had explained the error of his ways, he then went on to safely measure the voltage.

 

I still shudder to think of the effects of him putting (essentially) a dead short on a 195 Volt transformer - On a system rated at over 8Kw

 

As much as I agree with the above comments about "In Fluke we trust" I still have doubts as to what would happen to a hand-held meter carrying those sort of fault currents...

 

The point behind my ramblings here is that even with a decent meter, a three second mind f*rt can still result in toast.

 

Jim

[Jivemaster]

I wouldn't trust an inline fuse in a meter lead after my bro in law (who really does have a MA test suite tracable to standards) did a test on a supposed 1000a breaking fused lead which just lit up as an arc and stayed lit!

[dbuckley]

As much as I agree with the above comments about "In Fluke we trust" I still have doubts as to what would happen to a hand-held meter carrying those sort of fault currents...

Any meter with Cat III rating will have no difficulty whatsoever with a souce as puny as an 8KW transformer at 195V.

 

For more info, read Fluke's ABCs of Multimeter Safety (pdf).

 

For the avoidence of doubt: If you are going to measure stuff that has the potential of being high energy (so any measurement involving mains) if the meter (and the probes it came with) don't have Cat III 600V written on it then just walk away; your life may depend upon that decision. Cat IV is better than Cat III, Cat IV 600V is better than Cat III 1000V.

[JimWebber]

Any meter with Cat III rating will have no difficulty whatsoever with a souce as puny as an 8KW transformer at 195V.

 

Cheers David!

 

I am more then happy to bow down to your expert knowledge on this one, but from reading the article, it was hypothesised that the much of the destructive arc was possibly caused by the operator pulling the probe away and breaking the fault current. Would this still be a risk with a cat III or IV meter?

 

JW

[Dmills]

possibly caused by the operator pulling the probe away and breaking the fault current. Would this still be a risk with a cat III or IV meter?

Indeed, but if the meter had failed safe (open circuit) rather then turning into a short, that arc from the probe tip would not have been there to spread across the busbars and cause the explosion.

 

Incidentally on the subject of arcflash, those of you running older ETC Sensors with ED15s might want to have a look at the connection to the bottom circuit breaker in the modules, I have some that were more then a bit too close on the clearance, the slightly more modern ones are fine (as are these after a little application of additional insulation), but the early ones were rather scary if you have a stiff supply.

 

Regards, Dan.

[dbuckley]

... it was hypothesised that the much of the destructive arc was possibly caused by the operator pulling the probe away and breaking the fault current. Would this still be a risk with a cat III or IV meter?

Should not be as the fuse should open thus extinuishing the arc.

 

A lot of what the Cat III etc is about is ensuring that the overloaded fuse opens under conditions of high short circuit current. The energy released during the fault clearing process should not cause the instrument to lose structural integrity.

 

A Cat III meter can't protect you against bad things happening, but should ensure that the meter isn't the cause of the problem.