Single or DP RCBO (Debate continued, split from "old fuseboard" thread)

Andy™ said:

at least with an RCBO board, and fault will only take out the affected circuit and not half the circuits

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That would only be true when using DP Rcbos

I have split these posts (From "Need help, old fuseboard changed...........") so the debate can continue. They will only serve to confuse the OP

mainline said:

That would only be true when using DP Rcbos

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Not sure I agree with that

Murdoch said:

Not sure I agree with that

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An Sp rcbo will not clear an N to E fault.

mainline said:

An Sp rcbo will not clear an N to E fault.

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But only the affected one will trip.

Murdoch said:

But only the affected one will trip.

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A N to E fault can trip random rcbos.

mainline said:

A N to E fault can trip random rcbos.

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I have had that problem before looking for a fault on the wrong circuit

mainline said:

A N to E fault can trip random rcbos.

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Can but more often than not the tripped RCBO is the circuit with the fault

It's quite easy to talk at cross purposes here. The point about RCBO boards is the N's are joined upstream of the RCBO test coils that look for the imbalance.
Whether SP or SP with switched N this doesn't change.

That said, SPSN (DP) RCBOs are much more convenient for testing and fault finding and all new boards I fit use them.

Tim Howard said:

It's quite easy to talk at cross purposes here. The point about RCBO boards is the N's are joined upstream of the RCBO test coils that look for the imbalance.
Whether SP or SP with switched N this doesn't change.

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That’s true but a DP rcbo will isolate the circuit that causing the trip where as an SP one won’t.

mainline said:

That’s true but a DP rcbo will isolate the circuit that causing the trip where as an SP one won’t.

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That's what I thought you might have meant, hence my comment about cross purposes!

I used to think that DP RCBOs were more essential than they in fact are.
Detection is the same.
A L-E fault is isolated.
An N-E fault that isn't isolate by a SP RCBO will on many installations just be duplicating a TN link in the head. (There are exceptions of course!)
I'm more recently thinking that the main people who like them and benefit from them are us electricians!

DP rcbo is most beneficial in a TT earthing system where an upstream rcd is being used.