Low IR test readings on lighting and RFC.

[Piotr1000]

Hi,guys went to do an EICR and when doing IR test I got L-E ON RFC like 0.02 MOHM and two lighting circuits L-E AND L-N the results were like 0,14 and 0,15 MOHM.It is old wiring where all the cables live and neutrals are black put in the walls in steel conduit.My question is is it possible that low readings are due to dumpness in the wall?Took one light down and can see dumpness on the cables.Doe to time limit coulf not disconnect everything,but surely L-E and N-E should give some higher readings.Thank uou in advance for all help.

 

[pc1966]

Check if there are any RCD sockets/FCU on the circuit.

I have been caught before discovering they have a low-ish internal resistance to the CPC (presumably to trip if wiring fault?) and after disconnecting them it went to the ~10M or so I would prefer to see.

 

[westward10]

It is what it is. I will have a quick scan as per @pc1966 looking for obvious causes but aside from that record the figure you get. Forget L to N readings on an EICR.

 

[DefyG]

Filtered sockets or extension blocks always cause low IR readings on RFC's
Damp will obviously cause problems with IR but more likely at a termination than the actual cable (unless cable is damaged of course).

 

[pc1966]

Filtered sockets or extension blocks always cause low IR readings on RFC's

This is another good point. If you ever see low IR then re-test at 250V, if you get a really big difference (going from < 1M to > 10M sort of thing) then it has all the hallmarks of an SPD in some multi-way block or similar.

 

[buzzlightyear]

if you get a really big difference (going from < 1M to > 10M sort of thing

Ho master, maybe you could tell us what what sighs to look out for in low lr readings.

 

[mattg4321]

Surge protected extension leads usually give a reading of around 0.33Mohms in my experience. Change to 250v test and it disappears