UK Voltage in the cpc

[jeditricks85]

So had a call out last night to a house late night the lights had all tripped.
Had 2 lighting circuits in one breaker one with a dead short on it and the other is fine.

While i was there I also discovered there was 110v in one leg only of a cpc serving a final ring circuit but its not tripping the mcb I have to go back and go through it all has anyone come across this before and found it was something stupidly simple before I start breaking down every part of the circuit

 

[davesparks]

110V between the cpc and what?
measured with what type of tester?
Are you sure the voltage is real and not a phantom?

 

[jeditricks85]

110V between the cpc and what?
measured with what type of tester?
Are you sure the voltage is real and not a phantom?

between the earth conductor and the main earth, the live conductor to earth and neutral to earth. tested with a 1662 fluke multi functional tester calibrated and i checked it about 5 times

 

[littlespark]

On one leg of a rfc but not the other?
I don’t think you’ve got ring continuity there. The 2 legs should give near identical readings.

 

[Wilko]

Hi - if the circuit cpc is half way between L and N it implies (to me) it’s floating. And if it’s a ring final circuit that may mean more than one break in it.

 

[James]

As @littlespark says,
It looks like your ring is either not a ring or there is a break in it.
First check out the circuit whilst it is dead and repair the break in the ring continuity.
Whilst doing this, you might even find the reason for the voltage on cpc.
I am thinking it could be a mouse, a nail or other cable damage.

Finally worth considering, was there anything plugged into the circuit, some earth leakage from a pc could raise the cpc voltage.

Socket testers left plugged in can give rise to some strange readings when testing.

Also, you should not be disconnecting the cpc of a circuit that is energised. Any class 1 device plugged in can become lethal if there is a fault on the circuit.

 

[Lucien Nunes]

That section of CPC is floating; there must be at least 2 breaks as it should be connected at both ends. Any floating CPC will tend to take up a voltage somwhere between 0 and 230V from earth, due to the potential divider formed by its stray capacitance to the line and neutral conductors. Often it will be somewhat less than half the line volts as there's also capacitance to surrounding earth. If appliances with delta suppression caps are connected, it may be almost exactly half.

 

[davesparks]

between the earth conductor and the main earth, the live conductor to earth and neutral to earth. tested with a 1662 fluke multi functional tester calibrated and i checked it about 5 times

Test it again with an approved voltage indicator or a meter which ignores phantom voltages.
As far as I know an MFT will show a phantom voltage the same as a multimeter.