quick IR test question

[pushrod]

Am i correct in thinking that if you did an insulation resistance test part way along a radial back to the CU with it switched on and just the mcb for that circuit tripped that you should get a zero reading between N and CPC (with a TN-C-S supply).
cheers.

 

[a.e.s]

If the main switch is on, then yes, you will get a reading of 0

 

[pushrod]

cheers

 

[Mr Mark Sparks]

even with the main switch off unless all other circuits are clear readings from these will show on your circ

 

[ian.settle1]

Am i correct in thinking that if you did an insulation resistance test part way along a radial back to the CU with it switched on and just the mcb for that circuit tripped that you should get a zero reading between N and CPC (with a TN-C-S supply).
cheers.

You would on any circuit or type of supply as the N and E are connected to the star point at the supply transformer

even with the main switch off unless all other circuits are clear readings from these will show on your circ

As the main switch is normally DP then the is no connection between the N and E if switched off.

 

[pushrod]

You would on any circuit or type of supply as the N and E are connected to the star point at the supply transformer

Does that apply to a TT system as well?

 

[Mr Mark Sparks]

You would on any circuit or type of supply as the N and E are connected to the star point at the supply transformer




As the main switch is normally DP then the is no connection between the N and E if switched off.

what i was saying is if there was a fault on one of the other circs it would show on the one being tested hence why the need to discon the n being tested

 

[ian.settle1]

Does that apply to a TT system as well?

Yes as the path to the transformer is via the consumers earth electrode and the earth electrode at the transformer or how else would you have a path to allow the protective device to operate on a fault to earth?