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100mA RCDs TT system

Nikkid
Afternoon all,

What is the stance on using 100mA RCDs for TT systems now?

I was under the impression that they are no longer required as long as all circuits were protected by a 30mA RCD within the consumer unit (which in this case they will be).

Just looking for some clarity. 


Thanks! 

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    You'd still need them for any distribution circuits in TT systems. Likewise upstream of Metal cased CUs if you can't ensure double/reinforced insulation up to the 30mA RCD (e.g. for most split dual RCD CUs).  Some like to have a backup for the 30mA RCD too - as the failure rate isn't insignificant and unlike TN systems there's no relying on the MCB for ADS.

       - Andy.
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  • 0
    You'd still need them for any distribution circuits in TT systems. Likewise upstream of Metal cased CUs if you can't ensure double/reinforced insulation up to the 30mA RCD (e.g. for most split dual RCD CUs).  Some like to have a backup for the 30mA RCD too - as the failure rate isn't insignificant and unlike TN systems there's no relying on the MCB for ADS.

       - Andy.
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