RCD doesnt trip on test.

[Templer]

Hi I have a 6 way split load board located in the shed and served by 10mm SWA. Anything on the unprotected side of the board tests and works fine. However this is not the same for the protected side. I can plug a radio in and the circuit does not trip, but if I use the lawn mower or a drill the RCD trips immediately. In addition, the RCD does not trip when the test button is pushed. I have swapped out the RCD too. Nothing trips on the house board when the RCD in shed trips. All connections are secure in CU. Any ideas where to go next?

 

[Templer]

Hmmmmnnnn

See, if you also have the RCD in the main board supplying, you are still dividing the test current between two RCDs. It's a difficult one.

You really need to be able to IR test.

Do you have an unprotected way on the main board to connect the external board to?

Hi, I do, but I would have to move the SWA as it is at the opposite end of the board. What if I took to RCD out of the garage board. Would the RCD in the house CU (it is an exclusive one for this circuit) be sufficient?

 

[FAA Greenie]

Not only sufficient, but preferable. The RCD on the main board would protect the whole installation from the SWA to the final circuits.

Don't forget that when you remove the RCD you need to do full testing and notify the work though, you will be changing the characteristics of the circuit.

Also, removing the RCD is not going to cure the fault you probably have somewhere.........

 

[Templer]

Not only sufficient, but preferable. The RCD on the main board would protect the whole installation from the SWA to the final circuits.

Don't forget that when you remove the RCD you need to do full testing and notify the work though, you will be changing the characteristics of the circuit.
Also, removing the RCD is not going to cure the fault you probably have somewhere.........

Thanks for the advice. If the fault was anywhere other than the RCD in the garage board, would the RCD in the house CU not have tripped when a load was placed on the side of the garage unit that was not protected?

 

[Templer]

Morning, I have this morning removed the RCD in the garage CU. The board is now served by SWA via 40A MCB protected by 63a RCD. Reconnected the ring and nothing trips when load applied (drill) at either end of circuit. The RCD in the board was 80a, will the 63a on the house cu be sufficient? Also, would you change the 40a MCB or leave it as is? Thanks again to all those that offered their advice. This is a great forum

 

[Thomas123]

What tests on the protected side of the board have you done ?

The "switch the mcb on and if it holds it works" test

 

[somersetsparks]

Not only sufficient, but preferable. The RCD on the main board would protect the whole installation from the SWA to the final circuits.

Don't forget that when you remove the RCD you need to do full testing and notify the work though, you will be changing the characteristics of the circuit.

Also, removing the RCD is not going to cure the fault you probably have somewhere.........

I say that it would be perfectly acceptable to have the RCD at the supply end, however more preferable to have it at the sub-board in the garage, as if it trips you don't have to go back to the house etc. etc.
SWA would not benefit in anyway from RCD protection.
Either way its a garage, if its working now its all good