Part P testing

[LeeST]

Quick one,

The electrician wired my electrics in my new extension. The builder apparently told him they would be getting inspected by a third party (due to a mix up). so he tested and never recorded the results.

Anyway he's now coming back to do it, whats involved?

I ask as I have since fitted lightwave smart dimmers and the instructions say they must be disconnected if an "insulation resistance test" is carried out.

Will they be doing this?

 

[JohnW2]

I ask as I have since fitted lightwave smart dimmers and the instructions say they must be disconnected if an "insulation resistance test" is carried out. ... Will they be doing this?

Yes, they should.

Bring the dimmers to the attention of the electrician concerned and he/she should then deal with the necessary precautions - that may or may not involve their disconnecting the dimmers.

Kind Regards, John

 

[LeeST]

Thanks,

Apparently the tests were done but results not recorder as the builder told him a third party was carrying it out...……...

I hate builders

 

[JohnW2]

Apparently the tests were done but results not recorder as the builder told him a third party was carrying it out...……...

Well, although it's obviously too late to change that, I would personally regard it as daft.

If I were going to the trouble of doing testing (or doing anything else which produced 'results') I would record the results in some way, even if only in scribbles on the back of a cigarette packet 'just in case'! Apart from anything else, without such records it would be difficult to even attempt to respond to an accusation that the tests had not actually been done!

Kind Regards, John

 

[LeeST]

Well anything to do with this small extension I have had done as been a nightmare, the common thread being the builder who has arranged and overseen everything.

The nicest comment I could give him is that everything he has done has been badly organised.

In fact, he only seems happy when he has had to do just about every single aspect of it twice. I think he is slowly trying to do me in !!

 

[JohnW2]

Well anything to do with this small extension I have had done as been a nightmare, the common thread being the builder who has arranged and overseen everything.

Far from optimal 'overseeing', it would seem Mind you, as I'm sure you realise, you are very far from being alone!

Kind Regards, John

 

[LeeST]

Far from optimal 'overseeing', it would seem Mind you, as I'm sure you realise, you are very far from being alone!

Kind Regards, John

He see's ok, just fails to act or prevent.

Anyhow i'm not alone and this forum has been a godsend this last few weeks, its allowed me to get on and sort things or at least find out how things should be done before I get blinded with science which some people like to do.

Never again, ever!

 

[SimonH2]

Testing guidance has been changed and now allows for testing at 250V instead of 500V where items like dimmers may be damaged by the hugher voltage. But they may still have to be removed if they interfere with test results - and will have to be linked through in order to do full tests properly (so might as well just disconnect and stick the wires in a chock block).

 

[ericmark]

There is only one person who can issue an installations certificate and that's the person doing the work, it is the installation certificate which has all the test results on, the completion or compliance certificate can be issued by the LABC or scheme provider the latter can be either the person doing the works scheme provider or a third party scheme provider and it is possible testing to some extent is done twice once to fill in the installation certificate and also latter for the provision of the completion or compliance certificate where the person issuing it confirms the results, but always the installation certificate is completed by the person controlling the work.

 

[JohnW2]

There is only one person who can issue an installations certificate and that's the person doing the work, it is the installation certificate which has all the test results on...

True. It is perhaps not totally clear, but it sounds from the OP as if that is very probably what is going to happen (potentially confusing bits about a 'third party' removed from this quote)...

The electrician wired my electrics in my new extension .... he tested and never recorded the results. .... Anyway he's now coming back to do it, whats involved?

The OP will hopefully be able to confirm whether or not my interpretation is correct.

Kind Regards, John

 

[Risteard]

There is generally no reason that insulation testing cannot be carried out at 500V d.c. for the entire electrical installation with live conductors connected together and tested against Earth. Unless there are SPDs present then there shouldn't be an issue. (SPDs will test OK at 250V d.c. as they won't see this as a surge.)

 

[JohnW2]

There is generally no reason that insulation testing cannot be carried out at 500V d.c. for the entire electrical installation with live conductors connected together and tested against Earth.

That is true. However, if one wants to undertake 'comprehensive' IR testing, that really needs to include L-N testing - something which is not really possible (at any credible voltage) in the presence of any connected loads - because of the effect on the IR results (with any test voltage), as well as the potential damage to the 'loads' if the testing voltage is high.

Kind Regards, John

 

[Risteard]

That is true. However, if one wants to undertake 'comprehensive' IR testing, that really needs to include L-N testing - something which is not really possible (at any credible voltage) in the presence of any connected loads - because of the effect on the IR results (with any test voltage), as well as the potential damage to the 'loads' if the testing voltage is high.

Kind Regards, John

Of course it's true that testing between live conductors is not possibly with connected lamps/loads. However it is worth remembering that by far the most important test is the one to Earth anyway. In fact in much of the world it is the sole requirement.

What should always be remembered about insulation testing is that the minimum values quoted are for the entire electrical installation, or in the case of large installations each distribution circuit & distribution board with all final circuits connected - it is not a value for an individual circuit. So the requirement is actually much more onerous than many people appear to understand.

 

[JohnW2]

Of course it's true that testing between live conductors is not possibly with connected lamps/loads. However it is worth remembering that by far the most important test is the one to Earth anyway.

True, particularly when all the wiring in in T+E cable, in which case there is very unlikely to be a L-N 'leak' which does not also involve the CPC. However, if the installation involves any other sort of cables (e.g. 'flex', SWA, 'singles' etc.), then the possibility of an L-N fault not involving a CPC becomes greater - so, as I said, 'comprehensive' IR testing should include L-N.

BS7671 is rather contradictory on this issue. 643.3.1 clearly states (without any qualifications/exceptions) that an IR test should be conducted between live conductors, as well as between them and earth, but 643.3.3 says that if there are connected electronic equipment which could influence results, or be damaged, then only a test between (joined) live conductors and earth should be undertaken.

What should always be remembered about insulation testing is that the minimum values quoted are for the entire electrical installation, or in the case of large installations each distribution circuit & distribution board with all final circuits connected - it is not a value for an individual circuit. So the requirement is actually much more onerous than many people appear to understand.

True, although I'm not sure that I would personally describe the requirement as 'onerous'. Given the nature of PVC etc., I am fairly uncomfortable with any 'measurable' whole-installation IR (i.e. an IR which is not 'off the top of the scale' of the meter), and would be very uncomfortable with anything remotely as low as 1MΩ.

Kind Regards, John

 

[Risteard]

True, particularly when all the wiring in in T+E cable, in which case there is very unlikely to be a L-N 'leak' which does not also involve the CPC. However, if the installation involves any other sort of cables (e.g. 'flex', SWA, 'singles' etc.), then the possibility of an L-N fault not involving a CPC becomes greater - so, as I said, 'comprehensive' IR testing should include L-N.

BS7671 is rather contradictory on this issue. 643.3.1 clearly states (without any qualifications/exceptions) that an IR test should be conducted between live conductors, as well as between them and earth, but 643.3.3 says that if there are connected electronic equipment which could influence results, or be damaged, then only a test between (joined) live conductors and earth should be undertaken.
True, although I'm not sure that I would personally describe the requirement as 'onerous'. Given the nature of PVC etc., I am fairly uncomfortable with any 'measurable' whole-installation IR (i.e. an IR which is not 'off the top of the scale' of the meter), and would be very uncomfortable with anything remotely as low as 1MΩ.

Kind Regards, John

I certainly wouldn't be concerned with a measurable insulation resistance for the entire installation. One new installation recently had an insulation resistance to Earth of about 60 Megohms and rising, and another wired in new I.S. 201 cable (with insulated cpc) gave around 132 Megohms.

It certainly doesn't need to go off the scale - the entire installation is being measured in parallel so it's often unrealistic to expect that you will go off the scale of the meter, especially when plaster etc. may still be damp.

RECI Inspectors during routine inspections will invariably make you measure the insulation resistance of the entire installation in parallel between all live conductors connected together to Earth at 500V d.c. I agree with their approach as it mirrors what the Wiring Rules actually stipulate (and indeed BS7671 is worded very similarly on this).