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Type 'AC' RCD cable protection for SWA supplying a TT'd EV charger?
AJ Spark
6 Posts


I've just installed a 63A 3 phase supply to a dual EV Charger. In short its around 100m away, fed from PME to TT at the charger. 25mm 4c SWA. I couldn't get low enough Zs at the end of the armouring to disconnect via the MCB so I've added a 100mA S type AC RCD to protect the cable. EV charger has type A RCD's and 6mA DC detection built in.

Speaking to the NICEIC they advised I should have used at least a type A RCD. 

Now, as the 100mA S RCD is only to protect the cable what are your views? The charger will prevent more that 6mA DC but if 5mA flows is that enough to stop the 100mA RCD working as it's on the PME side? I'm not sure about the theory?

Cheers 😁

3 Replies
14 Posts

As you're relying on that RCD for fault protection I wouldn't be happy with it - I wouldn't consider it worth the risk. I also dont think it's compliant. In much the same way I wouldn't be happy with an EV charger with a Type A RCD inline taken off an AC RCD protected way on a split load board.

The DC leakage device has to disconnect at 6mA so as not to interfere with the operation of a Type A RCD otherwise we have to use a Type B. DC Leakage less than this could potentially have an effect on the AC RCD even in normal operation with less DC leakage.

What make is the RCD? I know some Wylex ones are stamped as AC but have been verified as Type A (I found some AC labelled ones in Type A boxes) and asked the question.

4625 Posts

If it was single phase I would say swap it for a 300 mA Type A RCD if the Ra is low enough, I’m not sure what is available as three phas.

4166 Posts

A real 100ma RCD will not be de-sensed to the point of non function by 6mA or even 12mA of DC. The trip point may shift by a few mA, perhaps even 10s of mA, but that is all. It may be a technical non compliance, it is not a real danger. To lock an RCD you need the DC to be a large fraction of the trip current, and even then there will be some larger fault current that it fires at.



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