domestic PIR no end to end reading on Neutrals

[freedomrun]

Domestic PIR (TN-S, 60A MAIN, 16MM EARTH, MAIN BONDING 6MM). Neutrals on end to end test at a S/O give zero ohms, Live gives 0.30 ohms & cpc gives 2.7 ohms at same S/O. I'm thinking that if this is a ring then the Neutral is loose somewhere on this cct. Any advice please - i may be overlooking the obvious - (i have measured 230v at all S/O on the cct) - Thanks.

 

[Octopus]

Time to start removing sockets and FCU's then!

 

[ezzzekiel]

Open neutrals would give a high reading not low sounds like additional path somewhere i would take readings from consumer unit end not at socket outlet

 

[freedomrun]

Agreed - would get a high reading on Neutrals if loose in the cct. The circuit is supplying some of the S/O in the property and not all - CU has three 2.5 T&E connected for use on S/O (already noted as too many on one protective device). Other ideas?

 

[oxocube]

Has the client agreed to pay for repairing the fault?

 

[freedomrun]

Customer is paying for any faults that require correction - also looking at CU swap when PIR done - just after advice on this zero ohm reading from Neutral as not had this before.

 

[oxocube]

I would suspect that neutrals have got crossed/mixed up with another rfc at the cu.

 

[freedomrun]

I will isolate the Neutrals on the 3 ccts supplying the rfc's at the CU - what if i still get a zero ohm reading when performing end to end check (I am getting 230V at all sockets) on Neutral conductors for these S/O's.

 

[HandySparks]

CU has three 2.5 T&E connected for use on S/O (already noted as too many on one protective device).

If you mean that there are three 2.5 T&E on one 30A or 32A protective device, then this may just be the two ends of the ring plus one unfused spur, which is an acceptable circuit arrangement. BRB Appendix 15.

 

[dagrat]

Additionally if we are talking 2.5mm twin then the cpc end to end seems pretty high, if line to line is 0.3, would have expected 0.5 ohms or less for cpc, depending on paralel paths.

 

[SPARTYKUS]

Domestic PIR (TN-S, 60A MAIN, 16MM EARTH, MAIN BONDING 6MM). Neutrals on end to end test at a S/O give zero ohms, Live gives 0.30 ohms & cpc gives 2.7 ohms at same S/O. I'm thinking that if this is a ring then the Neutral is loose somewhere on this cct. Any advice please - i may be overlooking the obvious - (i have measured 230v at all S/O on the cct) - Thanks.

Hello freedomrun - I assume you mean it's open circuit and therefore infinite ohms, not zero. Zero ohms would be quite nice really.

quick and easy way to make it safER would be perhaps to change MCB from 32A (if its this) to 20A. Depends what your remit is as said depends if you are there to fix faults or just report.

 

[ezzzekiel]

Reducing the mcb still leaves a broken conductor somewhere either record it for pir or locate break and make safe or repair the ring

 

[eddybs23]

Simple answer - you got a broken neutral in your circuit - you gotta find where (as already stated - start taking S/O FCU's apart)! Also cpc too high. R1 x 1.67 = cpc. (not taking into account parallel paths).

 

[SPARTYKUS]

Reducing the mcb still leaves a broken conductor somewhere either record it for pir or locate break and make safe or repair the ring

...or do as I said (reduce breaker size) depending on your remit

 

[GreenLightElec]

you could split the circuit into two 16a radials which would require disconnecting a leg of the "ring" at a S/O as you have continuity on the live and cpc?

As eddy mentioned your cpc measurement is too high and your max Zs will exceed 1.15 (assuming type B 60898 MCB) So you need to do further investigation and find out what is tapped into the original ring circuit. I would quote for 1 hours testing to investigate the fault which should be enough time to remove all points if required and carry out the remedial work to put the circuit right. Splitting the circuit should be plan B as more often than not, upon investigation, you will find a departure.

 

[ezzzekiel]

Reducing the mcb size would still leave a unterminated broken conductor lying around somewhere, the fault would need to be located and the damaged leg removed or repaired

 

[dagrat]

I agree with ezzekiel, finding the broken neutral is a priority if your leaving the cable in circuit.

 

[SPARTYKUS]

I agree with ezzekiel, finding the broken neutral is a priority if your leaving the cable in circuit.

And I agree with Ezzzekiel too, the point I am making is that dependant on your remit, i.e. what you can and can't or have been paid / asked to do, that might not actually be possible in the real world, in which case a five minute job to make it safer is to downrate the MCB. Maybe then on the two weeks until the job is put right and the fault traced, there is no chance of the cable being overloaded.

It depends on the job. I have for example PIR'd a house and reinstated a few things, and found the lighting circuit on a 40A MCB (wired in 1.5 T+E). The job was NOT for me to go fixing everything and setting the world and his dog to look like a carbon copy of the regs, so I disconnected it, turned it off, took pictures and made damned sure the owner understood why.

That was all. It's all very well saying what must be done, but sometimes it might take 6 months for it to happen. My post was meant to offer a slightly more tactical approach. The strategic would be to clear the fault :carolers:

 

[ezzzekiel]

Better clarification now i see the point you are making

But your original reply would appear to the op as leaving on a smaller mcb would suffice

Personally i would choose this option as a temp overnight fix if it was too late in day to repair the break

 

[SPARTYKUS]

Sorry didn't make myself clear. yes overnight would be ok. Would not want to leave a situation like that either.