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on the other there can be an issue when you have more than one RCD that you don't know which one will operate
I do remember you saying this but then it was a spark who was actually in my house so I'd rather blame someone who has been here rather than someone on the internet (not that I don't trust you, you've been a very helpful source of information). Also, all three times I've hired floor sanders (from two different places), they insist on also providing an RCD plug adapter without specifying it's only needed if your own house circuit is not already protected. That logic to me says "better safe than sorry", or "you'd rather have it an not need it, that need it and not have it", if that makes sense.
stevo_com-
they insist on also providing an RCD plug adapter
Presumably it is tested on some sort of schedule? Aren't you supposed to test your RCD every 6 months? Hands up all the people that do that.
Do they actually fail often?
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I wish I could remember why the teacher had such a hard on about it. 'RCD Contention' is the term I think.
I can't see a problem with it especially if it's you operating it since you know where all the RCD's are and would check to see which one operated.
jellybaby
Airhead
One the one hand you can never have to many RCD's, on the other there can be an issue when you have more than one RCD that you don't know which one will operate. During the course I took the teacher was quite keen on only having one RCD in each circuit.
These days the regs all point to RCBO's or AFDD/RCD combined per circuit in the consumer unit. It's now unlikely that anyone will have combined circuits in a single RCD because the combined earth leakage would be too high.
AFDD - Arc Fault Detection Device