40A RCD Garage incomer

11 Feb 2007
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United Kingdom
I have a Small Garage CU, Im using a 40A RCD as the incoming Main Isolator

I have a ring 32A in the garage.
6 A For Lights (including external PIR Floods)
I have a 10 A radial for the Freezer (Non RCD hence a seperate circuit Please dont give me jip about that. Im not putting a freezer on and RCD no matter what anyone says, its hard wired in anyway)

Anyway my concern is that that lot adds up to 48A. And My RCD is 40A. I cant imagine that it would ever exceed 40A and I suppose I could always protect the garage CU with a 40A MCB from the main CU but my question is do RCD ratings take diversety into account? and what would happen if more than 40A was put across that RCD. Burn my garage down or trip.

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It wouldn't trip, but it may get warm above it's rating. Make sure you use a suitably sized MCB at the CU in the house to prevent this.
Ah - you mean in the same way that in every split-load CU the MCBs downstream of the RCD never add up to more than its rating, and the RCD is always downstream of a protective device with a lower rating?

Good thinking.... ;)

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