Short in socket - why/how?

[davesparks]

However when I re-energised the circuit and plugged the appliances back in there was a crack, a small bang, and a weird (perhaps acidy) smell, which I understand to be a short circuit.

No, that is not a short circuit, that is two noises and a smell, these could have been caused by a short circuit or an earth fault.

A short circuit is a connection of negligible resistance between live conductors, an earth fault is a connection of negligible resistance between one or more love conductors and earth.

 

[TheJack]

Morning. So I've now carried out some IR testing at the board:

Neutral to earth = 0.43
Line to earth = 0.43
Line to neutral = 0.00

 

[westward10]

0.43 could be caused by an RCD socket or spur. It could also be a filtered extension lead (have you tested at 250v?).
Testing an existing circuit you should have your neutral conductors disconnected and linked to the line conductors, keep the cpcs connected. Do not test line to neutral unless everything is disconnected.

 

[TheJack]

0.43 could be caused by an RCD socket or spur. It could also be a filtered extension lead (have you tested at 250v?).
Testing an existing circuit you should have your neutral conductors disconnected and linked to the line conductors, keep the cpcs connected. Do not test line to neutral unless everything is disconnected.

Thanks Westward.

So how I've been taught to perform an IR test:

• CB safely isolated
• MFT in Isolation mode at 500v
• Zero by touching probes together
• Test N/E, L/E, L/N
• Probes at at top of breaker (for line) or terminals at top of board (for N & E)

 

[westward10]

That is fine for a new initial verification but this is an existing in use circuit. Your zero across L and N was probably something still connected across the circuit. Test as suggested in #13.

 

[TheJack]

0.43 could be caused by an RCD socket or spur. It could also be a filtered extension lead (have you tested at 250v?).
Testing an existing circuit you should have your neutral conductors disconnected and linked to the line conductors, keep the cpcs connected. Do not test line to neutral unless everything is disconnected.

Hi Westard. I've been back to this installation again.

Re "Testing an existing circuit you should have your neutral conductors disconnected and linked to the line conductors, keep the cpcs connected" - do you mean that at the board I leave the CPC connected and remove the line and neutral conductors for the relevant circuit and connect them with a jump lead? So as per the attached illustration?

Once I'm clear on that and I'm back at the installation I'll perform the test, but in the meantime I corrected a couple of mistakes I realised I had made with the wiring and retested as per post 14 and have different (better?) results:

Neutral to earth: >999
Line to earth: 0.31
Line to neutral: >999

As I understand it my Line to Earth is my issue as less than 2 mega ohms is a fail.

I've been around the ring circuit unplugging everything and identified a few accessories that I hadn't previously been aware of: a spurred electric radiator, its switch (which has a couple of neons), a socket with a USB port. I disconnected all these and - to maintain the ring - joined the relevant conductors (earth to earth, line to line, neutral to neutral) together with jump leads / wagos (which I presume was the correct thing to do???).

This made no difference however, the reading remained at 0.31.

One theory: 4 of the double sockets have tiny neon on/off lights on the switches - could that be responsible for the reading? Or am I simply overlooking something that's still in the circuit?

 

[brianmoooore]

I disconnected all these and - to maintain the ring - joined the relevant conductors (earth to earth, line to line, neutral to neutral) together with jump leads / wagos (which I presume was the correct thing to do???).

If you've broken the ring up, leave it broken and test the individual sections.

 

[TheJack]

Hi Westard. I've been back to this installation again.

Re "Testing an existing circuit you should have your neutral conductors disconnected and linked to the line conductors, keep the cpcs connected" - do you mean that at the board I leave the CPC connected and remove the line and neutral conductors for the relevant circuit and connect them with a jump lead? So as per the attached illustration?

Once I'm clear on that and I'm back at the installation I'll perform the test, but in the meantime I corrected a couple of mistakes I realised I had made with the wiring and retested as per post 14 and have different (better?) results:

Neutral to earth: >999
Line to earth: 0.31
Line to neutral: >999

As I understand it my Line to Earth is my issue as less than 2 mega ohms is a fail.

I've been around the ring circuit unplugging everything and identified a few accessories that I hadn't previously been aware of: a spurred electric radiator, its switch (which has a couple of neons), a socket with a USB port. I disconnected all these and - to maintain the ring - joined the relevant conductors (earth to earth, line to line, neutral to neutral) together with jump leads / wagos (which I presume was the correct thing to do???).

This made no difference however, the reading remained at 0.31.

One theory: 4 of the double sockets have tiny neon on/off lights on the switches - could that be responsible for the reading? Or am I simply overlooking something that's still in the circuit?

Bumping this up