Unexpected tripping

[magd36]

I just added a spur in my livingroom and something unexpected happened.

Firstly I tripped the breaker supplying the sockets and then wired the live, neutral and earth to the existing socket.

I pulled the cable to where the new socket is to be placed and the neutral accidently touched the earth. Low and behold the master trip for the whole house tripped!!!!!

I separated the neutral and earth and reset the master trip (while leaving the sockets breaker off). I then checked with a meter that there was no power being supplied between any of the 3 wires, which ther wasn't and deliberatly shorted the neutral and earth and the trip occurred again showing the whole thing was repeatable!! The master doesn't trip if the neutral and live are shorted nor if the earth and live is shorted, only if the neutral and earth are shorted.

I would have thought that once the socket breaker is tripped the wires could no longer have any effect on the remaining power and lighting circuits.

Can anyone explain. I'm presuming this has always been the case and not just because I've added some wire (as I've not even terminated the additional wire).

Thanks in advance.

 

[AndyPRK]

perfectly normal

 

[PrenticeBoyofDerry]

If the consumer unit is protected by an RCD or even that circuit is RCD protected. If neutral and CPC(earth) cables touch the RCD will trip, even when the circuit is isolated.

 

[magd36]

Thanks guys, this is reassuring. I can't say I fully understand why but guess it's in the mystics of how RCD's detect unbalanced circuits.

 

[echoes]

Nothing mysterious - when the MCB is 'off' the neutral conductor is still connected via the RCD:

Neutral_Earth_trip

• bernardgreen
• 16 Jan 2011
• 48

 

[magd36]

Understand. Thanks for that.