Anyone ever had a false positive testing for dead with...

[Geps]

I'm still confused as to why testing with a multimeter is dangerous when live checks are done before and after.......

 

[JohnW2]

I'm still confused as to why testing with a multimeter is dangerous when live checks are done before and after.......

It's not you. Provided one does the before and after proving checks, I can think of no rational engineeering reason (even taking into account the possibility of human errors such as having the meter on an inappropriate range) why use of a multimeter should be any more dangerous than a test lamp - even if the rules, regulations and guidelines don't accept that.

Kind Regards, John.

 

[333rocky333]

a multimeter should NOT be used to prove a circuit is live or dead.

Because?

On all H and S courses your told that, it is too easy for the meter to be on the wrong setting and the user getting a wrong reading

 

[JohnW2]

On all H and S courses your told that, it is too easy for the meter to be on the wrong setting and the user getting a wrong reading

That's only a danger if you don't do it properly - i.e. prove the meter both before and after your test.

Exactly the same is true using a test lamp. If you don't prove both before and after your test, that improper procedure can result in disaster just as easily as can a meter set to the wrong range.

A dangerous workman shouldn't blame his tools!

Kind Regards, John

 

[Geps]

a multimeter should NOT be used to prove a circuit is live or dead.

Because?

On all H and S courses your told that, it is too easy for the meter to be on the wrong setting and the user getting a wrong reading

I don't buy the mantra of 'the course said this so I don't do it that way' for the course to say that they must have some justification. If it's the for the wrong scale I accept but if I'm testing for live before hand I'm looking for a a 230ish reading...and I can't think of anything that would give that reading on the wrong gauge.....

Just to be clear - I'm not advocating ignoring best practice and proper procedures, just from my perspective I must know WHY it is that way to put my mind at ease....

 

[JohnW2]

I don't buy the mantra of 'the course said this so I don't do it that way' for the course to say that they must have some justification. If it's the for the wrong scale I accept but if I'm testing for live before hand I'm looking for a a 230ish reading...and I can't think of anything that would give that reading on the wrong gauge....

Exactly. I can't think of anything else that would do that, either. More to the point, no matter what range the meter was on, if (for whatever reason) it gave an indication of about 230 when known 230V AC was applied to it before and after the test, but indicated no voltage during the test, I'd be quite happy that the circuit tested was dead.

There's no doubt that the rules, guidelines and teachers are all determined to uphold this 'rule' and seem to be trying desparately hard (but to my mind not very convincingly) to find ways to justify it!

Kind Regards, John.

 

[333rocky333]

To be honest ive seen many engineers test for dead wrongly, by not testing or proving first, i think its more aimed at them people.

At least with a lamp theres more chance of them seing its live, before diving in, ive cringed when ive seen panel engineers work on busbars after just putting a multmeter on them and just seeing a zero reading.

Ive also been called out by oven engineers saying there units are dead, and a multimeter by there tools and my martindale shows all 3 phases live.

Sometimes it is worrying.

 

[JohnW2]

To be honest ive seen many engineers test for dead wrongly, by not testing or proving first, i think its more aimed at them people.

Indeed - but, as I said, one should not blame the tools for the actions of dangerous work(wo)men.

I don't see all that many electricians working but of those I have seen (virtually all in domestic environments), quite a few haven't routinely 'tested for dead' at all (unless they are uncertain about switches/isolators), a good few have tested with a lamp without any proving and a few have tested with a lamp after proving - but I don't think I've ever seen one prove both before and after testing. However, as I said, that's on the basis of fairly limited observations,so might not be a representative picture of what goes on in the world as a whole.

Kind Regards, John.

 

[TheGayOwl]

BLIMEY!

This is all turning into to some kind of HSE nightmare.... AGREED, MFT or multimeter fine for said purpose, which I suppose would not necessarily require calbration but simply proving....??

My argument would lean to Darwin... If testing for V you have the meter on the wrong setting and are wondering why it says 'error' or '0.44ohms' then get a zap then you are incompetent. The 'this install has two colours to BS7671' labels annoy the heck out of me. If someone cannot ascertain what colour does what and why then they should not be dabbling. Let em do so at their own risk. Darwin...populations are thinned out for a reason.

 

[333rocky333]

For anyone reading who may be interested

http://www.hse.gov.uk/pubns/priced/gs38.pdf

 

[JohnW2]

For anyone reading who may be interested http://www.hse.gov.uk/pubns/priced/gs38.pdf[/QUOTE]
Thanks. I've just had a quick read through and virtually of it is essentially very good common sense - most of which one would hope those using electrical test equipment would not really need to be told - but it does no harm to have it written down!

In the context of this thread, I note with interest that what is actually says about 'testing for dead' is:

to establish the presence or absence of voltage, the preferred method is to use a proprietary test lamp or 2-pole voltage detector suitable for the working voltage of the system rather than a multimeter.

... which seems appreciably weaker than the 'thou shalt not use multimeters' line that has been asserted in this thread! It easily could say "don't use multimeters", but it doesn't.

Kind Regards, John.

 

[securespark]

next with the back of the forefinger to make sure - dead as expected.

FFS. You got a death wish??

Do that again and you may well never return home.

 

[Spark123]

I'm still confused as to why testing with a multimeter is dangerous when live checks are done before and after.......

What if the circuit you were isolating had DC in it, a multimeter set to AC would register zero. Also, some meters will shut down if HF is applied to them.
That is why a proper set of voltage indicators needs to be used - they will register AC or DC volts without the user having to set them. I think proving units actually provide a DC source too.
I would get absolutely crucified at work and possibly sacked for using a multimeter on an isolation.

 

[Spark123]

i disagree.

If im isolating a manufacturing vessel to allow a mechanical engineer to enter the vessel and remove a disc dissolver, and i dont use the correct equipment to check the circuit for dead i am leaving myself wide open for prosecution if that dissolver was infact still live and was started by some unsuspecting operator. Against a dissolver you stand no chance of survival - 95 Kw of 3 phase motor with a 14 inch cutting disc on the end of the shaft.

I'd also try and start the machine afterwards to ensure the isolation as contactors will show the 3 phase to the motor as dead even if the supply fuses are fitted and isolator on.

 

[plugwash]

On many multimeters the 10A socket isn't fused at all. Yeah it's not a socket you use very often but even so you could still plug into it by accident. Even on ranges that are fused the fuses in cheap multimeters are often only glass cartridge fuses.

If you are going to be using a multimeter for mains installation work at least make sure you get a set of approved fused test leads for it.