Low IR reading

[Clinchy]

Hey people,

I did some testing for a sporadic RCD trip this week.

The customer did some playing about and narrowed it down to the garage.

Tested the garage circuits and all were good. Tested the feed and found with the CPC still in the bar I got 0.076 meg but when I pulled it out the fault cleared.

All I can think is it's chaffed through somewhere like maybe on a CH pipe? but just thought I would check I'm not doing something stupid before pulling in a new feed.

Cheers,

Luke.

 

[pc1966]

It going high with the CPC off the MET implies the fault is L to true earth, not the cable's CPC

So most likely insulation damage as you say but 0.078M is too high for a direct metal-metal contact to Earth, but an otherwise floating metal water pipe (i.e. electrically isolated from whole system by plastic sections), a charred cable (or fried rat remains), or a water filled accessory might explain it.

 

[pc1966]

Just to add, can you isolate the feed cable at the garage end and verify the fault is on that section, and not within the garage?

 

[Clinchy]

Thanks for the help PC, I went back today and found it.

The feed comes out the house into a junction box, under the path in SWA and into another junction box. When I looked in them last week everything looked good and earthed with a banjo at one end and the IR was high on that section.

I disconnected both ends today and check IR with a wander lead back to the MET and low and behold there was the fault, pulled the dust cover down and the SWA had been pulled out the gland on the banjo end ? Customer said she had the patio done a couple of years ago and he was in and out down the alley on a mini digger for days where the SWA was.

Thanks again for the help.

 

[pc1966]

Always good to hear the outcome!