Puzzler - Low IR

[sythai]

Just curious, think I know my answer here (apologies if this seems a bit basic for a 'real' spark)..... but

IR test on RFC at 250v : L to CPC and N to CPC giving some very low readings under 1Mohm.

Bit of a puzzler and checked all the obvious things, neons, tv booster etc. But it's just come me that there is an RCD spur which I completely forgot about.

Reckon thats got to be it.

Any thoughts please and thank you for your time

Sy

(ps - been one of those weeks, also in process of trying to locate a random RCD tripper on a another job. 2 or 3 times a day/night. Urghhh)

 

[Richard Burns]

Could well be the RCD spur, though it shouldn't give these results they do seem to do so.
Possibly a surge protector in place somewhere; does the problem resolve if you: disconnect the RCD spur (for RCD) or test at 250V (for surge protection)

 

[telectrix]

have you tried getting a continuity reading L-N? this would tell you if anything is connected

 

[sythai]

Could well be the RCD spur, though it shouldn't give these results they do seem to do so.
Possibly a surge protector in place somewhere; does the problem resolve if you: disconnect the RCD spur (for RCD) or test at 250V (for surge protection)

Back Monday so will give a try and see what happens.

 

[sythai]

have you tried getting a continuity reading L-N? this would tell you if anything is connected

Like that Tel thank you.... nice to add new things to my useful testing list.
Another which I always do on a CU change is continuity between all the lighting for any shared neutrals.

 

[Octopus]

RCD's in the the shape of the RCD socket or a RCD fused spur will often give very low IR in my experience, and it one of the things I look for when I see low IR.

Best remove it and see what happens.

I was trying to test a socket circuit yesterday - the readings suggested a connected load - but could I locate it - no. very frustrating.

 

[urbanmonkey]

Seen this with RCD sockets a fair bit, locate it, disconnect and try again I bet it will clear.

good call on the testing for borrowed neutrals! I always do it, amazes me the amount of people that don't. I check all the Neutrals not just lights tho, seen them robbed from RFC junction boxes in the loft before.

 

[HappyHippyDad]

Why would an RCD spur give low IR readings from Line - CPC, its not connected in any way?

I've had low IR readings L-N when I've forgotten about the RCD, but I dont think they've been low when tested to the CPC (not certain though!)

Can you remember the actual IR readings sythai?

 

[sythai]

Think they were both around 0.4 Mohm....

Sy

 

[Octopus]

Think they were both around 0.4 Mohm....

Sy

Defo whip out the RCD and test again!

 

[HappyHippyDad]

I'm going to bring all my years of experience to bear and say it's not the RCD and there is a fault somewhere.

Do let us know on monday sythai! :smiley2:

 

[sythai]

Sure will keep you posted chap :icon14:

 

[davesparks]

Most RCD spurs or sockets are of the 'active' variety and have an earth connection in to the gubbins of the RCD. And so they give bad IR readings.

Much the same as an RCBO with an earth connection can give funny numbers on an IR test.

 

[HappyHippyDad]

Come on Sythai!! What was it then? Dont leave us in suspense... :smiley2:

 

[sythai]

Come on Sythai!! What was it then? Dont leave us in suspense... :smiley2:

Sorry guys.... bit slow there coming back, certainly was the rcd spur this time :yesnod: