RCD to outbuilding

[plugsandsparks]

no..no and no again.....as a garage socket may be used for outdoor equipment....several ways to deal with RCDs in series....depending on the earthing arrangements
If a TN system then no upfront RCD would be required if you use an armoured cable....you would however use an RCD downstream..(garage)...


If a TT system then a high integrity C/U can be used with a 100mA s type RCD on its own.Then use a 30mA RCD at the garage end....this will give you the discrimination you need.....

Dont panic, was referring to the situation where the house is already covered by an RCD at 30mA, unless the garage cct comes away from rcd protection whats the point if the house always trips first because of other house leakage reducing the threshold of the house RCD.

 

[Richard Burns]

It will not always be the house first, the balance of probability is the RCD with the most circuits on it but the variability in the operating characteristically could invalidate this.
If a garage RCD trips at 18mA and the house at 26mA then the garage could go first. Then you have the response time if the house one trips in 100ms and the garage in 12ms the garage one could still go first.

And obviously vice versa, could be always the house.

There is no discrimination, similarly if you have a normal 100mA at the house and 30mA at the garage and the garage one trips slowly the 100mA could go first.