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Garage changed to granny flat.

Jonomac

Hi there. 

I'm converting my garage to a granny flat. I have a TNCS system in our house. Supply to 100amp main switch in consumer unit, fed down to 2 main RCDs feeding 5 mcbs each. 

The board in the garage is exactly the same set up. What's the best way to feed the garage from the main consumer unit. If I wire into an MCB which is linked to the RCD. This would feed the main switch in the garage leading to other RCDs. Same trip characteristics both would trip. 

The supply to the garage is by means of SWA cable.

Any design solutions would be grateful.

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    It's not just the RCDs that won't discriminate - of you feed the garage from an MCB, the MCBs likely won't either (unlike fuses, MCBs will de-latch as soon as the fault current is above their threshold, there's no natural delay according to rating).

    So my preferred approach would be to feed the new CU from a decent sized (e.g. 63A) HBC fuse. So if there;s the space, break into the tails, add a DP isolator is there isn't one already to act as single "main switch" for the installation, then split using service connectors (Henley Blocks) into the existing CU and a metal clad switchfuse (which you can gland the SWA to the garage into directly). e.g. www.tlc-direct.co.uk/.../index.html

       - Andy.

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  • 0

    It's not just the RCDs that won't discriminate - of you feed the garage from an MCB, the MCBs likely won't either (unlike fuses, MCBs will de-latch as soon as the fault current is above their threshold, there's no natural delay according to rating).

    So my preferred approach would be to feed the new CU from a decent sized (e.g. 63A) HBC fuse. So if there;s the space, break into the tails, add a DP isolator is there isn't one already to act as single "main switch" for the installation, then split using service connectors (Henley Blocks) into the existing CU and a metal clad switchfuse (which you can gland the SWA to the garage into directly). e.g. www.tlc-direct.co.uk/.../index.html

       - Andy.

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