Volts Between N And Earth

[installer44]

Whats the possible fault when you get a voltage between neutral and earth trying to sort a job where im getting about 15 volts.

[sparky999]

Whats the possible fault when you get a voltage between neutral and earth trying to sort a job where im getting about 15 volts.

Could be several faults such as water ingression or a trapped cable. If this is on a ring main you will have to break it down.

Pete

[luggsey]

Is it TT earth or PME, TT can do weird things as can PME faults.

Most likely cause is induced voltage, try turning off all other circuits and testing then.

I presume you have done 500 volt insulation tests?

[y-i-out-of-bed]

it could be meny things is there any IT equipment there? or could be earth leak from an applience or cable

[lawandorder]

It may not be faulty at all, what are the earthing arrangements?

[SUBS]

What are you reading it with ?

A DMM has such a high OPV that readings like tis can be confusing, try it with a 20,000 OPV analogue meter, or just put a resistor across the probes and see what changes. You might find there not a fault there at all, just some induced voltage, a reading through the capacitance in surge a limiter somewhere, or something like that.

[motco]

I seem to recall that neutral is earthed at the power station or local sub-station, and a small voltage can often be detected on the neutral conductor caused by the resistance of the neutral supply cable somewhere. Might be dreaming though...

[james.wilson]

you got a voltage on the neutral when the star point is not in the centre. This is caused by improper phase balacing

[DirectFS]

Whats the possible fault when you get a voltage between neutral and earth trying to sort a job where im getting about 15 volts.

Could be many things. Much depends on where you're taking your measurement from and how.

What else is connected to the circuit you've pulled your supply from? e.g. IT equipment, white goods?

Is the 15V measured at the board with circuits disconnected - e.g. is the fault on the supplier side or on the installation side?

It could also be poor connections, loose wiring, faulty wiring (e.g. a cable cut which has also cut inner sheathes), - an insulation test at 500V as someone said will answer that for you.

Someone also said that it could be reliant on the type of earthing arrangement for the installation - TT, for example, is earthed using copper rods driven into the ground, whereas with a TN type system, you have an earth supplied with the phase couresty of your friendly local supplier. As to how this is provided, depends on a number of factors - TN-C is supplied bonded to neutral (also known as PME) though arrives often as two seperate terminals - as in a phase, neutral and a tap for earth, so there should in theory never be any variance on the supplier side, whereas TN-S is supplied as a seperate earth. There are other earthing systems too, though not common in the UK any longer. Most of the UK is TN-C, though both TN-S and TT exist copiously in rural areas (especially where supplied by overhead cable).

So, without knowing much of the above, it is hard to give any sort of definitive answer......

Bill.

[luggsey]

I seem to recall that neutral is earthed at the power station or local sub-station, and a small voltage can often be detected on the neutral conductor caused by the resistance of the neutral supply cable somewhere. Might be dreaming though...

You could see this if the supply company neutral is high z and you or someone on the same supply phase has a neutral earth fault, the difference in potential will make really weird things happen!

James your description of a star point not being in the middle baffles me, can you explain what you mean a bit more?