Faulty light circuit

[Cp93]

Have just moved into a house. Old re wire-able fuse box has been replaced. One of the circuits keep tripping the RCD. 

Basically the circuit (3 lights) is fed off the boiler switch. The boiler works fine, only the 3 lights fed from the boiler switch are causing the RCD to trip.

There is continuity between all of the light switches, 240v between L&N though only 160v between L&E.

There is however only continuity between lives from the light switches and live at the boiler switch. No continuity between neutral and earth at any lights and the boiler switch. 

Assuming the fault must be the wiring  between the boiler switch and first light switch on circuit but can’t see any loose terminals. Any ideas ?

 

[Murdoch]

Have you got any test kit? If not you will probably need a local spark to fix this for you

 

[Cp93]

Just a meter. Spark fitted the board yesterday he is back out today as his head was gone trying to sort it yday, just looking for advice really but understand without seeing the set up it would be difficult for anyone to say.

 

[Murdoch]

Sounds like you have a borrowed neutral. 

Very comon to find in older installations, and RCD s won’t tolerate them

 

[Cp93]

Would putting both circuits on the same RCD resolve this ?

 

[kerching]

Well it "might" negate the problem but it won't "fix it"

 

[ProDave]

"160V L to E" probably means the earth is not connected.

A spark properly competent to replace a consumer unit should be able to sort this out without his head spinning. Worst case is those 3 lights need rewiring. I would personally prefer the lights and the boiler were not on the same circuit anyway.

And your spark should have all the test equipment needed.

Note the use of the word should.  It may be yours is not properly competent?

 

[Cp93]

"160V L to E" probably means the earth is not connected.

A spark properly competent to replace a consumer unit should be able to sort this out without his head spinning. Worst case is those 3 lights need rewiring. I would personally prefer the lights and the boiler were not on the same circuit anyway.

And your spark should have all the test equipment needed.

Note the use of the word should.  It may be yours is not properly competent?

Think it was just a long day,  both light circuits now on the same RCD and this has stopped the tripping. 

 

[ProDave]

Think it was just a long day,  both light circuits now on the same RCD and this has stopped the tripping. 

That has just confirmed you have a borrowed neutral from one lighting circuit to the other. It has not "fixed" the fault.

I hope he sorted out the earth or did he sweep that under the carpet as well?

 

[Doc Hudson]

Think it was just a long day,  both light circuits now on the same RCD and this has stopped the tripping. 

Long day, or even long week, should have negligible bearing on the type of fault you describe. It is absolute basic every-day bread & butter sort of situation any competent electrician could identify and clear, (or propose remedial work to clear later). However I would have though it could have been identified during the testing before energising the circuit? ProDaves   assumptions sound very accurate to me.  "A spark properly competent to replace a consumer unit should be able to sort this out without his head spinning".  

Doc H.

 

[Murdoch]

Think it was just a long day,  both light circuits now on the same RCD and this has stopped the tripping. 

That may have stopped the RCD tripping but it won't stop some unsuspecting sole getting a belt off the neutral at some point in the future ....which could kill

What does the installation certificate say about this?

 

[kerching]

What does the installation certificate say about this?

opcorn  ️