UK RCD Tripping

[Davem83]

Evening, came across a fault today on a new board that’s been fitted by a previous electrician. Split load dual RCD 6 way Hager board, when a fused spur is switched on or when the boiler starts up the RCD trips but the circuit is on the other RCD. Have checked the all wiring at the DB and all is ok. The previous board was a old wylex 100ma RCD board and never tripped.

 

[Mike Johnson]

Neutral in wrong block on board?

 

[Davem83]

All neutrals are in their correct place.

 

[Mike Johnson]

Sounds like you have a cross over somewhere or a faulty RCD, have you done a ramp test of both RCD's.

 

[Dustydazzler]

Borrowed N ?

 

[Davem83]

Borrowed neutral was my thinking. However the previous electrician fitted a single 30ma RCD board before this board and it still tripped. Earth leakage is too high for a 30ma RCD, but why would the other rcd trip and not the rcd protecting the circuit?

 

[loz2754]

One possibility is damage to cables lying next to each other from circuits each from a different RCD. Insulation test would help rule this out.

 

[brightlight]

Does the boiler have an external Pump, Timeswitch and Thermostat? Is it a System Y or S System? If so could it be that there is more than one supply feeding the Boiler Time Switch and Control wiring, both fed via different Circuits and RCDs.

 

[Grant1987]

Evening, came across a fault today on a new board that’s been fitted by a previous electrician. Split load dual RCD 6 way Hager board, when a fused spur is switched on or when the boiler starts up the RCD trips but the circuit is on the other RCD. Have checked the all wiring at the DB and all is ok. The previous board was a old wylex 100ma RCD board and never tripped.

I had a similar problem couple of years ago. RCD2 was tripping whenever any load was put on kitchen ring baffled me. I carried out insulation resistance test and found that the fault was on the downstairs lights which was on RCD1 screw touching neutral in living room light. It was also a Hager split load board. Do an IR test on circuits that will find the fault for you.

 

[UNG]

Had a fault similar to this about a year ago and the fault was on one of the circuits off the RCD that was tripping, had me puzzled for a while especially when I did an RCD test on the incoming side of the RCD's and it tripped the RCD, fault was found using a cable locator to be a floorboard nail partially through a cable

 

[telectrix]

N-E fault could be on one of the circuits that is on the RCD side that is not tripping. take the suspect N's out of bar and IR test.

 

[Mike Johnson]

Yes a N-E fault, I had that many years back with a pinched neutral in a double socket, I admit it was a socket I had installed. can't find the embarrassed emoji, so ?

 

[telectrix]

last 1 i had was shower switch N-E fault. switch on kettle (on the other RCD) and it tripped.

 

[Deleted account]

I bet that old 100ma rcd was seazed. The fault was probably there before.

or

@Davem83 idea of boiler pump on separate circuit on opposite RCD is a real good bet.

 

[Davem83]

So yesterday the owner disconnected a lighting circuit from the side that tripped and everything worked fine, didn’t trip once.
my tester is being calibrated at present once it’s back I will carry out the tests.