Thanks for all the help, I didn't that a cooker switch could be used - makes sense I guess, after all it's just an isolator. Many thanks for all the help.
Shower MCB
- Thread starter hansPulesh
- Start date
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1 final question. I think this was why the system was set up with a 40amp MCB rather than the required 45amp one.
I've been speaking with the electrician who fitted it and he advised me that the manufacturers do not make a 45amp MCB. Thisa was why he fitted a 40amp one instead.
I want to know if a 50amp MCB can be used instead of a 40/45amp one?
The shower guide says a 45amp MCB should be used but if this is not available, can a 50 amp one be used instead?
The consumer unit is made by CPN.
I've been speaking with the electrician who fitted it and he advised me that the manufacturers do not make a 45amp MCB. Thisa was why he fitted a 40amp one instead.
I want to know if a 50amp MCB can be used instead of a 40/45amp one?
The shower guide says a 45amp MCB should be used but if this is not available, can a 50 amp one be used instead?
The consumer unit is made by CPN.
That would depend upon the size and routing of the cable - your electrician will be able to advise.
People will argue about how crucial it is to follow manufacturer's instructions to the letter (the regulations are changing nect year to give electricians more discretion in that respect). However, speaking personally, I think that (assuming the cable could support it) to have a 50A MCB would be the lesser of the evils than having an (under-sized) 40A one.
Kind Regards, John
Whilst that is true when installing in the first place, it is not going to make any difference to this situation as the current drawn by the shower is not going to be any different than it is now.
Agreed.
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Despite the feelings of you and I, I suspect that that many electricians (including those undertaking EICRs) will think solely in terms of "In ≤ Iz ≤ Ib" (per 433.1.1), rather than 433.3.1(ii), and therefore would not be happy with In being greater than Iz of the cable ... but maybe I'm wrong in suspecting that!
BTW, I'm not sure why you make an exception of "installing in the first place" - one could surely invoke 433.3.1(ii) even then, if one were so inclined, couldn't one?
Kind Regards, John
They may but that would be lack of knowledge.
Yes, perhaps I should not have made the distinction.
I just meant that when installing initially the method of installation and derating factors would be considered but it is not going to make any difference now whether In is increased as the current drawn is going to be as it has always been - i.e for the OP's information NOT limited to 40A.
Perhaps - or maybe they have a different judgement as to whether a shower could create an overload.
I'm still not sure that I see any real difference between 'then' and 'now'.
Kind Regards, John
Thanks for that, but what about the 45amp isolator switch which is in place? If a 50amp mcb is fitted, could this not be dangerous as the isolator switch has a max rating of 45amps?
I suppose that some people who think very strictly might see an issue, and you could find a 50A isolator switch if you were really concerned.
However (if I dare say this!), if one bears in mind that even a 45A MCB will allow about 65A to flow for about an hour before tripping, I'm not sure that it is an issue that I would lose any sleep over. Perhaps more to the point, the only real potential electrical issues relate to the current that the isolator might be called upon to break (i.e. if it were switched off whilst the current was flowing) - and with your shower, that will be below 45A, anyway.
Kind Regards, John
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