Insulation resistance testing with no cpc

[bigbaddave]

Even with the lack of a CPC on any particular circuit I would still be testing between L-E and N-E. When conducting IR tests it's called earth for a reason, we're not meggering the CPC, we're meggering the earth, ie. from the line conductor to the earth bar or MET and the same for the neutral conductor. What if somewhere on a circuit with no CPC the cable has been damaged enough through whatever means so that one or other of the conductors are in connection with an exposed or extraneous conductive part? Or what if there's a nice fat screw through the cable linking it to another circuit? In my humble opinion, there's a multitude of reasons why we should still be conducting the IR tests as required.

I totally agree. However testing L-Cpc and N-CPC doesnt test the lighting circuits does it if there is no cpc. L-N is the only test which can prove the condition of the cable in this case..

 

[D Skelton]

I totally agree. However testing L-Cpc and N-CPC doesnt test the lighting circuits does it if there is no cpc. L-N is the only test which can prove the condition of the cable in this case..

If you read my post again you will see that I made a clear distinction between a cable's CPC and Earth in general. When IR testing a cable with no CPC, as well as the obvious L-N test you would carry out on the cable, you should also be carrying out L-E and N-E. Imagine one scenario; the cable has been damaged and the line conductor is exposed and resting neatly on a hot water pipe. How will just a L-N IR test pick this up?

 

[bigbaddave]

If you read my post again you will see that I made a clear distinction between a cable's CPC and Earth in general. When IR testing a cable with no CPC, as well as the obvious L-N test you would carry out on the cable, you should also be carrying out L-E and N-E. Imagine one scenario; the cable has been damaged and the line conductor is exposed and resting neatly on a hot water pipe. How will just a L-N IR test pick this up?

Ah me sees, It wont. Sorry I assumed that you meant this was replacing the L-N test.. N- earth is allways done globally (for me) as it takes less time than doing individually. Only if the reading was less than 2 meg then id be testing individually..

Normally for CCU change and a load of lamps then L/N - Cpc is done globally a) When pricing up and b) When its finished..

 

[lodmoorhill]

When doing a CU change and lights have no cpc. ... What would you do?

Follow the advice in the ESC Best Practice Guide No1, Issue 2.