How to "insulation resistance test" procedure????

[Carter]

Testing the circuits individually
lets say that test above is for testing from the tails, so when doing it individually do you have to remove the cpc and neutral, use a croc clip for them and use the probe onto the breaker?

If for instance you are testing between N and E from the N-bar and E-bars you will read the cumulative parallel insulation resistances or faults from all of the connected neutrals to their associated and other grouped cpc's. Nothing wrong with that per-se but you won't be reading the individual circuit's I.R. reading You need at least one of them Neut or CPC disconnected.

can the test be done, having the supply isolated, all breakers on. and testing by using the probes onto the earth bar & neutral bar.
neutral bar & isolated side of the main breaker? is this ok?

Yep! Page 36 of Guidance Note 3 says...

Simple installations that contain no distribution circuits should be tested as a whole.

- (my emphaisis)

If you haven't got a copy it further adds...

The tests should be carried out with the main switch off, all fuses in place, switches and cct breakers closed, lamps removed, and flourescent and discharge luminaires and other equipment disconnected.
Where the removal of lamps and/or the disconnection of current using eqpt is impractical, the local switches controlling such lamps and/or eqpt. should be open.

To perform the test in a complex installation it may need to be sub-divided into its component parts.

So yes you can test the installation as a whole and so long as 0.5Meg is achieved it is compliant although a reading below 2Meg would indicate a possible latent defect and would require confirmation that is a consequence of normal circuit functioning.
Diags of the procedure on pages 38/39 of GN3

If testing the whole board at the tails then you need the supply to the board OFF i.e its main switch and tails de-energised and the board's mainswitch in the ON condition.

If the supply to the board cannot be removed just lock the mainswitch off at the board and test the whole shebang from the switched side of the isolator. (now dead/use proving unit before and after)

If testing individual ccts at the load side of their breakers you need the board isolator OFF and LOCKED and the circuit's breaker set to the OFF state or you will read the paralleled I.R.s of other ccts back through the busbar.

thankyou in advanced, please quote where i've gone wrong cheers

no one like to add...?

The only thing is don't just switch off, LOCK IT OFF! and then put the key in your pocket/on your keyring, don't leave it on top of the board. You'd feel a right chump if the assessor taps you on the shoulder and hands you the padlock.

 

[LukeScotty]

nice one carter.. much appreciated

 

[hmiddity]

hey, could some explain how to do an insulation test, to niceic Test standards, of how you should do it when YOUR being assesed. correct procedures, aimed at those whos just done it and passed cheers

Hello, Just read your comments. I am in the same position. I have a feed from the lighting circuit to a fused double pole switch which goes to a transformer for a shower pump.
What would the effect be if the neon lights and transformers were left in place?
Regards and thanks for any advice

 

[telectrix]

you could not IR L/N as the transformer and neons would give a low reading. all you could do would be join L/N and IR to E.

 

[hmiddity]

you could not IR L/N as the transformer and neons would give a low reading. all you could do would be join L/N and IR to E.

Thanks for your reply.
My electrical system has a new consumer unit with two rcds. Some of the wiring is quite old and is gradually being replaced.
In one of the mcbs I have two wiring circuits, 1) is for some lighting and 2) is for the doorbell and an understairs light. Neither of the circuits has an earth cable. Also the line and neutral are separate cables. What is the best way to determine which line goes with wich neutral?
Thanks in advance for any help.