L-E reversed and low voltage on RFC

[diced carrots]

Trainee here so it's likely I've got my wires crossed!

I've got a small unoccupied rental property which had a rewirable fuseboard which my work colleague (fully qualified spark) and I replaced the other day with an 8 way RCBO board, surge protected. He did the board change while I replaced some sockets with USB charging sockets.

Initial end to end testing on the Ring Final indicated that there was a break in the ring somewhere, so we swapped out the 32a breaker for a 20a. All circuits were holding fine on the RCBO's after we went home on Friday evening. The plan was that I would come back today to investigate the broken ring, carry out some testing and to label up the board.

So, when I got back to the property today I plugged my socket tester into a socket and it indicated Live Earth Reversal. I pulled off all the sockets to check they were all wired correctly and they all looked good. Using my MFT I tested the voltage between L-N and it showed 60v, between N-E voltage was 190.

Any ideas?

 

[Pete999]

Trainee here so it's likely I've got my wires crossed!

I've got a small unoccupied rental property which had a rewirable fuseboard which my work colleague (fully qualified spark) and I replaced the other day with an 8 way RCBO board, surge protected. He did the board change while I replaced some sockets with USB charging sockets.

Initial end to end testing on the Ring Final indicated that there was a break in the ring somewhere, so we swapped out the 32a breaker for a 20a. All circuits were holding fine on the RCBO's after we went home on Friday evening. The plan was that I would come back today to investigate the broken ring, carry out some testing and to label up the board.

So, when I got back to the property today I plugged my socket tester into a socket and it indicated Live Earth Reversal. I pulled off all the sockets to check they were all wired correctly and they all looked good. Using my MFT I tested the voltage between L-N and it showed 60v, between N-E voltage was 190.

Any ideas?

Done any r1 r2 testing?

 

[ipf]

Sounds like a neutral problem...and if you've a break in the ring, where's the place to start?
What are the ring continuities?

 

[diced carrots]

Done any r1 r2 testing?

Not yet. Was called home to other duties before I could get stuck in!
[automerge]1582477287[/automerge]

Sounds like a neutral problem...and if you've a break in the ring, where's the place to start?
What are the ring continuities?

I've been right through the property all sockets off and terminals checked. I found one that was pumped full of silicone but I replaced that one with a new socket and the fault remained.

Also, all sockets worked until we changed the board. The previous tenant had damaged a few sockets and had removed one, but I think I've accounted for all of that.

 

[snowhead]

I think the answer is obvious, but did you test before the board change, if so were the L-E, L-N, N-E results the same as now?

And have you checked the connections for the Ring in the new C.U?

 

[marconi]

diced carrots: a clear opening post - well done Sir.

 

[telectrix]

socket testers will often show L-E reversal if you have a floating N. that's where the fault is. a poor connection somewhere on N. do a end-end on N and then track it down by splitting the ring.

 

[static zap]

L-N and it showed 60v, between N-E voltage was 190.

If the voltages are stable with socket tester present ,
and they add to aprox 250 .
Something is floating up , due to presence of socket tester.
One of your notional ref points is actually a mid point voltage !
Think potential divider.

(2nd half of post self supressed -involved wagos ,a socket and fly cables --stay safe )

 

[Strima]

Had the exact same last week, broken neutral and disconnected CPC.

 

[diced carrots]

Thanks all for your help, it's much appreciated!

I've been back to the property this evening and tested the circuit.

• End to ends were 0.64 (r1) and 1.11 (r2).
• L-N tests at sockets ranged between 0.30 and 0.36.
• L-CPC ranged between 0.39 and 0.48
• Zs 0.66

When I screwed the conductors back in to their terminals in the CU the original fault rectified itself. I suspect there might have been a loose connection at the Neutral terminal?

 

[Megawatt]

Had the exact same last week, broken neutral and disconnected CPC.View attachment 55947

That black wire looks burnt not broken

 

[Strima]

That black wire looks burnt not broken

Overheated, possibly due to a loose termination however the screw terminal was damaged so I was unable to check.

 

[Lucien Nunes]

OK, so you found a disconnect or a likely disconnect in the neutral, which was also indicated by your odd L-N and N-E voltages (both readings involving the neutral were wrong but the L-E voltage presumably OK). However, the socket tester reported a different kind of problem than the actual one present, which was confusing. L-E reversal is clearly very dangerous and in practice rather unlikely, so the first thing to think about in that situation is 'what is the test actually trying to tell me'. Socket testers are not very intelligent!

BTW, please always give the units when stating measurements:

L-N tests at sockets ranged between 0.30 and 0.36

If those numbers are ohms, I would make one diagnosis. If they are megohms, I would make another. Put a different way, would you be worried if I dropped something on your head that weighed 0.36?

 

[Pete999]

OK, so you found a disconnect or a likely disconnect in the neutral, which was also indicated by your odd L-N and N-E voltages (both readings involving the neutral were wrong but the L-E voltage presumably OK). However, the socket tester reported a different kind of problem than the actual one present, which was confusing. L-E reversal is clearly very dangerous and in practice rather unlikely, so the first thing to think about in that situation is 'what is the test actually trying to tell me'. Socket testers are not very intelligent!

BTW, please always give the units when stating measurements:


If those numbers are ohms, I would make one diagnosis. If they are megohms, I would make another. Put a different way, would you be worried if I dropped something on your head that weighed 0.36?

Right on Lucien!