Plug in RCD downstream of an RCBO CU

May 29, 2020 Last reply: 6 years ago 6 Replies

Hi All,



Since my "power" circuits got upgraded to the then gold standard 17th edition about 10 years back with all circuits on RCD or RCBO protection, I've consigned my plug in RCDs to the cupboard.



But I'm wondering if having a more local RCD (40 foot nearer the tool) is something worth doing if using electrics outdoors?



What does the team think?



TIA



Chris


You won't normally get any discrimination so either the local, upstream or both could trip, however look at the follow ups to "F" (Frank's) thread this morning, there could be an argument for an "active" second RCD purely for the latching action.

it won't add anything, other than ability to trip if the main one fails. Possible but not likely.

NT

Your plug-in RCD may be more sensitive than your fixed RCD/RCBOs, e.g. 10 mA vs 30 mA, which would give some extra protection for outdoor use.

If the plug-in RCD is electronic it might trip faster than the fixed one and give discrimination. If it's electromechanical then it won't.

(Discrimination is the ability for the closest protective device to a fault to trip. In this case discrimination would mean the ability to have the plug-in RCD trip rather than the one in the distribution board.)

Nope...

Just two devices to go reset if you get a trip!

I think you have got the terms mixed up (or just missed a word out).

An active RCD is non latching ie trips with a powercut

A passive RCD is latching ie will not trip with a powercut

they're normally 30mA though

I don't think that's likely.

NT

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