RCD Tripping

[Jeffjb]

Hi all
I have had my garage connected to my home electrics.
However, when anything is plugged into any of the sockets and switched on, the house RCD trips. The garage RCD and breakers do not trip, just the house one that the armoured cable connects to.

My electrician is away til October hence I am trying to troubleshoot in the meantime.

Does this sound like a neutral earth leak or something else??

 

[Mikegh]

Off the top of my head

Fault with supply cable

Fault at garage and garage rcd is stuck on my la

 

[Dartlec]

Is it possible to get a pic of both consumer units?

Is the house end one an RCD that protects all circuits? If so, it may be close to it's tripping value most of the time, such that only a small leakage is enough to trip it, but not the garage.

Are both RCDs 30mA? It would be unusual to have armoured cable protected at the house end with RCD - then to have another RCD at the garage end, unless they are different values (with the house one 100mA perhaps, and the garage 30mA). If they were both 30mA then I'd usually expect the garage one to trip first, assuming that everything has been installed correctly, but the sensitivity of RCDs can vary, which is why you don't usually want to daisy chain them.

If the garage electrics have been installed recently then the cabling should have been tested to ensure there were no faults in the wiring. Do you have an electrical certificate for the garage install?

It's hard to narrow down without the right test equipment, but if this is a new install I'm wondering if there has been an error connecting the SWA, or at one of the sockets so that Live and Neutral are swapped or something similar.

Is it only socket circuits in the garage, or are there other circuits (eg lighting), that work correctly?

 

[Jeffjb]

When I press the test button on the garage RCD it trips.
The supply cable was brand new armoured and sealed at both ends.

 

[James]

sounds like possibly a N in the wrong bar of house board.

 

[Lucien Nunes]

My money is also on what he said^^

What testing was done on completion? Assuming you have been issued with an EIC, can you post the relevant bits, excluding personal and contractor's details.

 

[Mikegh]

Oops yes correct above

Didn't spot it was a new connection

Still shouldn't be happening on new work

 

[Marvo]

Yup, I'll also go with the theory it's connected to the wrong neutral bar in the house CU. This does however mean that the garage has never had power points that don't trip and the garage installation has never been properly tested after it was connected.... It also means the installer shouldn't be working unsupervised.

 

[James]

Sounds so similar to a friend that called me out.

new oven (second hand), had wired it in himself as a replacement.

his words were, I just copied the wires from the old oven and when ever i turn it on the rcd trips. (oven clock would work but as soon as a light or heater was turned on, click went the rcd)

I take the cover off the oven and the oven supply plate, All looks fine.
spend an hour testing the oven elements, wiring and lights etc.
cant find any problems IR is all above 2M ohm

scratch my head for a bit, ask are you sure you have done nothing else?
NO, nothing else he says.

Just to satisfy my curiosity, I open the DB cover and spot the N in the wrong bar of a split board.
So I ask him again, ARE YOU ABSOLUTLEY SURE that you have done nothing else?

oh yes i did disconnect the cooker supply cable to make sure it was safe whilst I connected the new cooker, but i put it back the same so i didn't think it was important.

Grrrrrr, not sure if i should slap him for keeping that piece of info to himself or myself for not looking there earlier!!!

 

[pc1966]

Yup, I'll also go with the theory it's connected to the wrong neutral bar in the house CU. This does however mean that the garage has never had power points that don't trip and the garage installation has never been properly tested after it was connected.... It also means the installer shouldn't be working unsupervised.

Yes, a basic socket tester would give the all-OK but using a MFT would certainly trip it on the high current PSSC aspect even when the PFC test is using a low non-trip current.

Edited to add: Above assuming N-E swapped at sockets or N in wrong bar.