Napit assesment coming up, some advice please

[flameport]

D. Will they want to see locking off devices used on mcb's and signs?

Hopefully not.

Signs are of no value to anyone, they can easily be removed, not read, not understood.
MCB locking devices in a domestic environment are generally cack as well - a good many can easily be removed without tools or the key. Then there are those countless installations where it is impossible to fit such things.

The proper method for isolating the circuit is to remove the line and neutral conductors from the MCB / neutral bar / RCBO or other device and put them in the earth bar.
This ensures no one can switch the circuit on, avoids the whole-house RCD tripping when you mistakenly connect N&E together when removing a socket, and it means you can confirm the circuit you disconnected is the correct one (test for continuity between the three conductors), and it also eliminates any possibility of that circuit becoming energised from some other source such as when two or more circuits are connected together due to fools and blunderers having worked on it previously.

 

[flyingsparks]

D. Will they want to see locking off devices used on mcb's and signs?

The proper method for isolating the circuit is to remove the line and neutral conductors from the MCB / neutral bar / RCBO or other device and put them in the earth bar..

Yes I agree, but then to do the polarity check, you would need to disconnect the neutral (if doing by r1+r2) because else you could be reading the result of r2 + rn.

 

[ban-all-sheds]

What if you accidentally set your multimeter to current instead of voltage and then shove it straight across the incommer?

I was waiting for someone to come up with that one!

Indeed.

The moment I read this

A multimeter set to the wrong range is no more dangerous than a test lamp with a dead lamp/bulb.

I thought "not so".

 

[ban-all-sheds]

All I was really wondering is if I need to go out and waste my money on something like a voltage proving unit, which I have never had a need for, or will need in the future. I always test on the live supply present before isolation(where possible and fe to do so)

So you never need to test for dead in a location where you do not know that you have a live supply present?

 

[JohnW2]

The moment I read this

A multimeter set to the wrong range is no more dangerous than a test lamp with a dead lamp/bulb.

I thought "not so".

You are taking my comment out of context. Maybe I was not clear enough but when I talked of 'dangerous' I was (meant to be!) specifically refering to the risk of getting a dangerous ('false dead') answer to a 'test for dead'. As I went on to say, in either case one can only be confident of one's test for dead if one proves the test device immediately before and imemdiately after the actual test. Just like a test lamp with a dead lamp, a multimeter on an inappropriate range will fail the provong test.

In view of some of the reponses I got, I would also re-iterate that I personally do not regard 'proving' as 'proper proving' if it uses DC to 'prove' something that is to be used to test for AC. OK, with a lamp, it's not going to make any difference, but with anything electronic, it could theoretically result in catastrophic outcomes. It's not as if it's that difficult to create an AC proving unit.

Kind Regards, John

 

[Wontdothatagain]

Just from a DNO perspective,

We are ONLY allowed to use a Drumond test lamp for testing for dead. This MUST be "proved" before and after testing with an compatible proving unit.

We are not allowed to use any other instrument as has previously been said, they can be set wrong, batterys flat, defective.

With a drummond as long as you prove it before and after testing, you cant go wrong and the "error" factor is negligible

 

[JohnW2]

Just from a DNO perspective, We are ONLY allowed to use a Drumond test lamp for testing for dead. This MUST be "proved" before and after testing with an compatible proving unit.

That sound very reasonable, and as I would have expected.

We are not allowed to use any other instrument as has previously been said, they can be set wrong, batterys flat, defective.

That is also 'as expected', but ....

With a drummond as long as you prove it before and after testing, you cant go wrong and the "error" factor is negligible

... isn't it really true of any device used for testing for dead that "... as long as you prove it before and after testing, you cant go wrong" (even it is set wrong, has flat batteries or is defective)?

Kind Regards, John

 

[Wontdothatagain]

isn't it really true of any device used for testing for dead that "... as long as you prove it before and after testing, you cant go wrong" (even it is set wrong, has flat batteries or is defective)?

What i was trying to get across was with other instruments, there is still a degree of error that can creep in but with a drummond and a proving unit, it is pretty much idiot proof

With a Drummond, the lamp either works or does not, if it does not, you investergate, if it lights up, you are good to go.

With digital displays, you are looking for something different and the lack of something can be interpeted for something else

 

[JohnW2]

isn't it really true of any device used for testing for dead that "... as long as you prove it before and after testing, you cant go wrong" (even it is set wrong, has flat batteries or is defective)?

What i was trying to get across was with other instruments, there is still a degree of error that can creep in but with a drummond and a proving unit, it is pretty much idiot proof

Yes, I realised that, but was questioning whether a test lamp really had a monopoly on that.

With a Drummond, the lamp either works or does not, if it does not, you investergate, if it lights up, you are good to go. With digital displays, you are looking for something different and the lack of something can be interpeted for something else

Maybe. I have to say that if I was tempted to use a multimeter, I'd be more inclined to use an old-fashioned analogue one.

Of course, an insuperable problem is that, even with a test lamp properly proven before and after use, there is still scope for human error creeping in - since the easiest way to fail to detect voltage which is present is to fail to establish satisfactory contact between the probes and the test points (probably more of a potential issue with a lamp than any other type of device) - but that's an inevitable consequence of any testing when the 'safe' result is 'nothing happening'. What would be ideal would be a device which would 'do something' (rather than 'do nothing'), which it would only 'do' if there was satisfactory connection to the conductors, when there was no voltage, but there's no really practical way of achieving that.

... not that any of this will change my personal practice from using a lamp!

Kind Regards, John