Short between N-cpc of another circuit?

[Flakey]

I have a lighting circuit on one RCD and ring on other RCD I'm getting neutral of ring to earth of lighting circuit fault. But clear IR between Neutral of ring and cpc of ring as far as I know the circuits are and should be electrically separated. All cables tested are tested out of terminal bars as neutral and earth are connected on the intake. Any ideas appreciated. All I can think is maybe a nail between two cables I.e lighting circuit and ring

Cheers

 

[Octopus]

What work has been done in the property? Is it a new build? Refurb?

Need a bit more information matey

 

[Farmelectrics]

do full test on all circuits one at a time you'll soon identify the fault

 

[Octopus]

do full test on all circuits one at a time you'll soon identify the fault

I think he's done that!

But he should leave all the CPC's connected when doing IR tests!

 

[Flakey]

What work has been done in the property? Is it a new build? Refurb?

Need a bit more information matey

Its a new build mate.

 

[Octopus]

Sounds like bob the builder has stuck a nail or screw in!

Now who is going to pay for your time for the investigation?

 

[Flakey]

I initially did test on each circuit 1 at a time and there were no faults to the individual circuits. Only when i powered up the the board first RCD with lighting stays on second RCD with ring tripped when Lightin circuit MCB is switched on. Initially thought was a case of crossed neutrals in the board which has turned out not to be the case. So IR test between all of the ring cables and earth bar identified Lighting cpc as culprit pulled cpc from earth bar and pulled neutral of ring tested between them dead short. I mean all i can think at this point is a screw or something similar may have gone through grouped cables skinning the cpc in one cable and neutral in the other thus creating a dead short. But i want to make sure im not over thinking before i start cutting through newly painted walls . will be breaking the circuits down tommorow as i had a painter in the apartment today wanting light.

Thanks again for any help

Cheers!!

 

[Flakey]

Tbh im on day rate but its one of those were you want to get to the bottom of the problem with as little destroying as possible lol!!

 

[telectrix]

then you first need to split the RFC down to find which section has the fault. then get the hammer out.

 

[Flakey]

then you first need to split the RFC down to find which section has the fault. then get the hammer out.

Yes mate done the split hammer is in my bag seems like its gonna be demolition derby

 

[tony mc]

You say dead short what reading are you getting 0.00Meg or are we talking low ohms ?

You need to start doing a bit of maths and testing to get as close to the fault as possible before ripping everything apart !

 

[Octopus]

Tbh im on day rate but its one of those were you want to get to the bottom of the problem with as little destroying as possible lol!!

So you can take as long as you like? best you get the clients approval on this matey!

 

[7029 dave]

Did you run the cables?, do you know the runs, I would bet it's going to be on route to cu the finals where they are bunched together, or somewhere where the 2 cables are running together.

 

[SJD]

You need to elaborate on the phrase "dead short". Is this 0.00 Meg, on an IR setting, or some very low Ohm reading on continuity?

If there is a nail or something connecting CPC of one to N of another cable, then you should be able to measure the resistance in Ohms, likely some fraction of an Ohm. You might well be able to use this reading to estimate how far along the cable run the fault is, remembering of course the different CSAs of the two cables.