Rcd trip

[currie123]

Hello, been at a job today where I am adding in new lights,fan etc into new bathroom.

old rewirable db, with a 4way rcd board added in for downstairs bathroom .

So, to cover my work I ir tested upstairs lights circuit with the intention of moving this circuit to the 4way rcd board , all ir testing results tested ok, but when I connected into rcd board and attempt to put any load onto the circuit (switch a light on) then the rcd trips.

Relatively inexperienced when it comes to fault finding and I understand the borrowed neutral problem causing issues when two rcd's as per new17th board, but couldn't understand why the rcd tripped in this instance?

The 4way rcd board is supplied by 16mm tails which have been split so supplying both the old rewirable board and the new 4 way rcd board.

anyone help ?

thanks

 

[rich.250]

Neutral to earth fault! Well sounds like it from your description.
It will hold till load is applied.
Only happened since the lights have been added?? Then must be the lights.

 

[Octopus]

Borrowed neutral on the landing?

 

[currie123]

That's the thing tho I haven't connected anything new to circuit yet, just stripped out some old wiring not required any longer.

Can't think that anything I did in that respect has caused a problem.

Just was left scratching my head this afternoon as to if I'd missed anything simple as to me both the rcd board and the old rewritable still had a common neutral so couldn't understand why the rcd would trip

 

[currie123]

Yes I'm thinking probably borrowed neutral but as both the rcd board and the old Wylex rewirable board supplied from same neutral block I couldn't see why ?

 

[rich.250]

If its a borrowed neutral then it would trip because the line and neutral aren't balanced at the outgoing side of the Rcd.
If that makes sense??

 

[currie123]

Ok rich I think I understand il need to do a bit more homework on this scenario. Frustrating thanks tho

 

[Englishsparks]

Test between the neutral for the lights that keep tripping and the other neutrals on the consumer unit. Will determine if it is borrowed.

 

[rich.250]

No worries.
Test between neutral bars and look for interconnection. If not, then there may well be a n-e short.
Drawing out the situation may help you understand why it trips when the neutrals are connected wrong.

 

[currie123]

Yeah ok cheers will do my best

 

[martinxxxxxx]

Turn the whole lot off at the main switch - safe isolation procedure, then separate the lighting neutrals out of the board and test to see if there is any connection between them at low ohms and then at IR. if there is that is your problem, if not put the then you will need to test that the live going out on the live to upstair only comes back to the neutral upstairs - to do this with the neutrals still disconected (but put in chock block to be safe) power up the upstair live and check for voltage on the upstairs neutral and the downstairs neutral (when a light is switched on upstairs) if it comes on both they are interconeected, if it comes on the down neutral you have a borrowed neutral. Google it and you will find loads of diagrams and remedies. Good luck