This question concerns fitting RCBOs in a 17th Edition board already having two RCDs installed. It has been answered by ABB (Theme – Distribution Equipment):
Question: I've been asked to install RCBOs. This is the first time that I've used them. It will be on a 17th Edition board having two RCDs.
I understand the need for the white tail to the circuit protective conductor (CPC) etc., but how do I fit them into the board.
Should I install the RCBOs before RCDs - could you please advise?
Answer: If you have a split board with two RCDs fitted, there is no need to fit RCBOs - this would be like protecting each circuit twice and it will be a toss up whether the RCD or RCBO trips first.
If the RCBOs are fitted after an incoming device (typically just an isolator), then they will protect each circuit individually - so the device that trips will only be the one associated with the circuit having the earth fault.
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