Live Neutral Reverse Fault

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Hi Guys,

I could do with some advice from you fine people. Today I was spurring off a socket in the lounge of my house that I’m renovating. After adding the new socket I tested it with a plug in socket tester. And it came up with a ‘Live Neutral reverse’ fault. I checked the socket and it was wired up correctly. So I went around testing more sockets and found all the ones in the Lounge and the master bedroom to be in the same fault. Never tested them before. I have all the sockets away from the wall atm, so had a look and they are all wired correctly. The house is empty and there is very little plugged in

There are two circuit loops in the house. I switched off the one that supplies the good sockets so could see which loop was affected. There are some sockets on the loop that are reading correctly.

Would it be the case that some sockets would have a Live Neutral Fault and some be reading ok on the same loop?

After that I isolated the RCD unit. Opened it up and had a look. All the Live red wires where going into the top of the MCBs and all the neutral black wires where going to the neutral bus bar. All earths connected to the earth bus bar. Everything seemed to look ok.

So I disconnected the two live red wires from the top of the MCB of the affected main loop and checked them for continuity. No problems. Then I checked to see if I was getting any readings across the live and neutral. Found to be an open loop on my Fluke.

What am I missing here. Can anyone shed some light onto what’s going on I’m pulling my hair out today and my usual electrician is flat out busy and not answering his phone.

Is there something else I can try before ringing round to try and bring in help? Should I lift the floors boards and look to see if the is a JB i don’t know about?

Thanks

Alan
 
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Have you tried taking all the socket fronts off, perhaps on one or more of them the wires have been swapped around ?
 
With a cheap plug in tester you can testing if the line or neutral is same as the earth, for this to work the earth must be at neutral polarity, so the tester can't show if the line - neutral is swapped or the earth is missing and has enough capacitive and inductive linking to be an line polarity.

The more expensive types do use a load so less likely to show the wrong results, but still using a plug in tester may show there are unlikely to be faults but you need to use proper meters to be sure of the results.

I would start testing with no power switched on and standard test procedures.
 
I recall mine saying reverse polarity when it was not, i think a combination of other facters relating to the N and E causes it, i would usually then use my other tester to safely check voltages L to E, L to N and N to E
 
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You'd need 2 stealth wrong jbs to replicate your fault- going to be much easier to use your meter to test L-N, L-E and N-E at each socket before digging the floor up. Or (not meaning to be rude) how is your colour vision-black/red colourblindness is quite common
Did wonder whether this was going to be a whole house reverse polarity job- ran into that one in Mountain Ash in Welsh Wales years ago, apparently the whole street was originally supplied with DC from the mine engines, when AC came along someone cocked up!
 
If there is a break in the N or E loop then the first job is to find that I would say.

As said, the way the testers work, they can mis-display the cause of other faults.


Daniel
 
A floating CPC will be displayed as L&N reversed by a plug in socket tester.
 
A floating CPC will be displayed as L&N reversed by a plug in socket tester.
Althoiugh one hears quite a few disparaging comments about plug-in testers, I think that one thing to be said of them is that, apart from N-E reversals (which they admit cannot be detected), I think they will usually (always?) show some abnormality (even if not the right one) if anything is wrong.

In other words, if they show no faults, then I think one can be be fairly confident that there are no faults (other than, possibly, a N-E reversal - which could also be missed by other methods of testing).

... although I suppose someone is probably now going to cite scenarios in which that is not necessarily true!

Kind Regards, John
 
Althoiugh one hears quite a few disparaging comments about plug-in testers, I think that one thing to be said of them is that, apart from N-E reversals (which they admit cannot be detected), I think they will usually (always?) show some abnormality (even if not the right one) if anything is wrong.

In other words, if they show no faults, then I think one can be be fairly confident that there are no faults (other than, possibly, a N-E reversal - which could also be missed by other methods of testing).

... although I suppose someone is probably now going to cite scenarios in which that is not necessarily true!

Kind Regards, John

Yep its just another weapon in the arsenal of test gear to be used wisely
 
Hi Guys. Thanks for all the responses. here is a follow up.

I had the electrician round and it was found to be an earth fault. I realised that when changing a socket in the month I found a snapped earth and I had to repair it with a connection block. As tradesmen had been using the socket (its away from the wall due to decorating) it had popped out the connector. after repairing again the fault went away.

But its seemed strange as a break in the loop wouldn't normally show a fault as there are two paths for the earth in the loop. we tested the circuit and it is still showing an open circuit on the earth. So Im guessing there had always been a break somewhere and I caused a second break. Giving rise to the fault.

Goes to show these testers see a fault but don't really know what the fault is, as my head was thinking Live - Neutral Reverse.

Now I have to hunt the the broken earth. When the earth from the socket became disconnected all sockets on circuit showed a fault except the with the broken earth which was fine. So my conclusion is the break must be somewhere in between the consumer unit and first socket.
 
Now I have to hunt the the broken earth. When the earth from the socket became disconnected all sockets on circuit showed a fault except the with the broken earth which was fine. So my conclusion is the break must be somewhere in between the consumer unit and first socket.

Probably your easiest way to find the break, is by starting at the consumer unit and parting the two ends of the ring (power off!), then check for continuity between the two ends. Then use a long length of wire on one of the meter probes, so you can test from the CU earth, to the earth terminal of each socket in turn, until you either find the break or get to the far end of the ring.
 
Years ago around 1990 we had a problem of how to test 110 volt supplies had an earth, at this time there was no simple tester made, so I made one with LED's diodes resistors and neon, The two LED were wired lines to earth so with no earth neither would light, but neon wired line to line so it showed there was a supply even if no earth, it did work, but when propriety models came on the market I stopped using it.

With 230 volt testers I think around 6 mA to earth and 6 lamps with three having two colours, it always seemed odd to me that the first lamp lights between zero and 1.7Ω when with a ring pass limit has never been more than 1.5Ω. But with the loop test suppose they are reasonable testers, however I seem to remember they were withdrawn at one point, and a recall was issued, as to why not a clue, but Martindale would not have done it without reason.

Some makes even have a RCD tester
socket-and-see-sok36-tester-angled.jpg
not sure how they can be class II when it needs an earth to work? But both
Martindale-ez150.jpg
testers do a reasonable job and it is unlikely they will show too many wrong results, however as well as these testers there are also a whole host of cheap and nasty ones, some made by the same firms who make the versions shown. Problem is they are all called socket testers, and we have no idea how good the one being used is.

Unless there is a little load, even if only 6 mA, it is likely to pick up capacitive and inductive linked voltages and give wrong readings when an earth wire has become disconnected, they neither tell you the supply is OK or the supply is faulty with any certainty. However suppose better than nothing, I would be happy using one in my caravan, but would not be happy using one instead of proper meters as a work tool.
 

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