I guess the only additional reason would be that it trips faster than the one on the house CU... For convenience... But perhaps no safer
It will not necessarily trip any faster, it would be a toss up, as to which tripped, or both could trip.
I guess the only additional reason would be that it trips faster than the one on the house CU... For convenience... But perhaps no safer
That's obviously true - but IF, for whatever reason, the OP wants to continue feeding the gazebo from a circuit which is protected by a 'house RCD', there would then really be no significant downside of having the second RCD he proposes. In fact, I would have expected that you would have been one of the last people to criticise someone who wanted redundancy of protective devices?Which means a fault in the gazebo could suddenly and without warning plunge the house into darkness. A hazard to people in the house. .... Feed the cable to the gazebo from its own RCD and MCB ( or an RCBO ) in the CU in the house to avoid that hazard,
is good, but when one of them can unnecessarily cut the power to an entire house instead of just the gazebo then the use of two may not be sensible.redundancy of protective devices
Sure - but, as I said, I was talking specifically about the situation in which, for whatever reason, it had been decided to feed the gazebo (with or without an additional RCD) from an RCD in the 'house CU'.is good, but when one of them can unnecessarily cut the power to an entire house instead of just the gazebo then the use of two may not be sensible.
As you say, that goes without saying - but that is a scenario that we haven't even considered.It goes without saying that to have an RCBO in the house to protect the cable to the gazebo ( and nothing else ) with an RCD in the gazebo would provide the redundancy of protection.
In that situation, there is virtually no downside to an 'unnecessary' downstream additional RCD. On the contrary, there is at least a chance that the downstream one, but not the upstream one, would trip in the case of a fault (thereby not 'plunging the house into darkness). If, as is quite likely, both were to trip, that's not significantly different from reliance on just the 'house' RCD, the only difference being the need to also reset the downstream one.
At some level of precision, that is essentially inevitable since the probability of two devices having absolutely identical thresholds, to the nearest picoamp/picosecond or whatever, is close to zero. However ....Having been in this situation, the usual scenario is that one RCD proves to be a little more sensitive than the other ...
... because 'moving parts' are involved, there is a finite time between when the device is 'triggered' and when its contacts open. That means that there is a time-window (of continuing current flow) during which the second one may also be triggered., so that one will always be the first to respond, first to disconnect.
I probably agree that the most common situation is probably for one RCD to operate, but the other not. However, it is far from unknown (at least, in my experience) for both to operate.
I would agree .... I'm not so sure that the latter situation is as rare as you seem to imply. The residual current does not need to be 'much larger' for that to be the case - merely larger than the trip threshold of the less sensitive RCD.I would surmise, that under a low but increasing level of current leakage, the usual fault condition, that the same RCD will always be the one to trip - the more sensitive one. Under a much larger current fault condition, then it becomes a race, between the two, the first to disconnect, or more likely both disconnecting.
The degree of "need" is in the eye of the beholder. As above, some people derive reassurance from redundancy of protective devices - not all that unreasonable in this case, given that failure (or failure to remain in-spec) of RCDs is far from unknown.Indeed, but you still don’t need that second RCD.
They may or may not be right.I contacted the supplier and they said I need an RCD Type B... Rather than the standard Type AC.
In the Uk, traditionally Type AC but, now, increasingly Type A. I think it would be pretty (very?) unusual to find a Type B.What type of RCD is usually in the consumer unit of a normal house?
They may well not exist (although I dare say that someone will pop up to demonstrate that they do )Equally I can't find any outdoor RCD of type B.
Whilst I can't argue about the theory, I suspect that is because you are probably being over-concerned/over-cautious (in comparison with most other people). I would strongly suspect that the vast majority of users of these lights would never even consider thee sort of issues you are raising.Going round in circles now haha
I take your point, but I think these are semi-professional/commercial lights and are expected to run up to 1000m which is why they run LEDs on 240V DC.
See above. I'm not convinced that the situation is necessarily any different in sets of LED lights intended for domestic use/users.So the average dosmetic user wouldn't realise the difference
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