Potential difference between Earth and Neutral

[Gigsy]

Has anyone ever encountered a fault with a RCD which causes a potential on earth in respect to neutral?



I am a trainee electrician, working with an experienced electrician. We encountered a fault today, earth had a potential of 238V in respect to Neutral and a 0 V potential in respect to line.



We did an insulation resistance test at 500V on all circuits from line to neutral, line to earth and neutral to earth. All circuits gave a resistance of >999M ohm. So there is no way line and earth can be crossed anywhere.



The fault didn't trip the RCD or the MCB, yet there was a potential difference between neutral and earth.



We got really strange voltage readings while probing around, differences between earth and neutral ranging from 100v to over 300v, how can this be as nominal voltage was 238V.



The potential difference between neutral and earth was greater when the RCD was in the closed position.



All I can possibly think of is the somehow the line windings around the iron core in the RCD have made contact with the Neutral windings. Could a fault like this possibly create a voltage on Neutral, and cos it is a TN-C-S system, Neutral is connected to earth at the incoming supply, so is it possible this voltage could be seen on the earth bar in the consumer unit?

 

[Barry White]

Line and neutral reversed ?

 

[PEG]

Hi dude,no guess would be possible,without knowing where you were measuring this voltage,and what position all the various switches/breakers,etc were in.

Start from a position upstream,where all measurements are as expected,or if not,somebody has a bigger problem

 

[Gigsy]

I just would like to know if anyone thinks it is remotely possible a fault inside the RCD could cause this issue?

 

[Octopus]

You've posted this on another forum.

Why didn't you test Ze?

 

[HandySparks]

I just would like to know if anyone thinks it is remotely possible a fault inside the RCD could cause this issue?

I don't think it's even remotely possible.

 

[Gigsy]

You've posted this on another forum.

Why didn't you test Ze?

Yes I got a temp ban on this forum, so I joined another one. You use two forums too, else how would you know?

We didnt suspect the issue to be with the distributor.

 

[Gigsy]

Line and neutral reversed ?

Line and Neutral reversed coming into the distribution board?

That could make allot of sense. We didn't do a live polarity test thinking about it.

 

[dmxtothemax]

it's more than likely a ghost voltage !

 

[Bobster]

Sounds like a floating neutral to me.

With the earth connected to the DNO's incoming earth, what resistance are you getting between N > E

 

[Octopus]

I'm gob smacked that 2 sparks and 1 trainee didn't check the incoming supply...... all sounds a bit smelly IMHO

 

[Gigsy]

Sounds like a floating neutral to me.

With the earth connected to the DNO's incoming earth, what resistance are you getting between N > E

> 999 on 500v

 

[Gigsy]

Sounds like a floating neutral to me.

With the earth connected to the DNO's incoming earth, what resistance are you getting between N > E

>999 on 500V

 

[Octopus]

So Gigsy..... are you going to update this forum with your findings reported on the other forum?

 

[Gigsy]

So Gigsy..... are you going to update this forum with your findings reported on the other forum?

Is that necessary? I don't think anyone would be interested? Is it frowned upon to use two forums? If so why do you use more than on forum? Which forum do you like the best? Why are you making an issue with me using two forums?