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Sub main and TT

Grumpy
I am dismayed that I have to ask but it is so long since I worked in a TT area that I am doubting myself.

I'm running an SWA submain to an outbuilding so instead of the usual switch fuse should I be using a 100mA S RCCB and a 63A mcb?

The armoured passing directly through the outside doesn't necessitate a 30mA RCD does it (as I have been so advised)

Apologies and thanks.

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  • 0
    The disconnection time is one second rather than the five seconds required for a TN earthed installation, which you will achieve with a slugged 100 mA RCD or a 300 mA RCD.


    I have been using 300 mA Type A RCDs, but those who know about these things have said that using a S-Type 100 mA Type AC RCD upfront of a 30 mA Type A RCD is not an issue.


    It’s no wonder that people get confused about “types” of RCDs ?
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  • 0
    The disconnection time is one second rather than the five seconds required for a TN earthed installation, which you will achieve with a slugged 100 mA RCD or a 300 mA RCD.


    I have been using 300 mA Type A RCDs, but those who know about these things have said that using a S-Type 100 mA Type AC RCD upfront of a 30 mA Type A RCD is not an issue.


    It’s no wonder that people get confused about “types” of RCDs ?
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