Shower circuit design.

davezawadi (David Stone): 
 

I see no part of BS7671 that says a 32A breaker may not be fitted, although it may be slightly unwise from a convenience point of view. Andy, you are putting forward slightly odd views, the case size of a 63A breaker is the same as a 32A one, so why do you think it may “overheat”? That is exactly what its thermal section is supposed to do to switch off small overloads, and the actual heat load for all sizes is exactly the same! You are falling into the “I don't like the look of that” trap, you may not but it is not dangerous in any way, and if the breaker trips, that is exactly what it is designed to do. I suspect too that Andy J is missing a point, the faster trip time is fairly unlikely as the thermal section is pretty accurate, because it also needs to be very repeatable, and there is no advantage this being quick, although there may be for the magnetic part as contact wear will be reduced. As usual, the question brings up many other pieces of knowledge and information that are largely unconsidered.

It is a good thing you did not have this as a question in your Wiring Regulations exam.

433.1.1 (i) The rated current setting of the protective device (In) is not less than the design current (Ib) of the circuit

davezawadi (David Stone): 
 

I see no part of BS7671 that says a 32A breaker may not be fitted, although it may be slightly unwise from a convenience point of view. Andy, you are putting forward slightly odd views, the case size of a 63A breaker is the same as a 32A one, so why do you think it may “overheat”? That is exactly what its thermal section is supposed to do to switch off small overloads, and the actual heat load for all sizes is exactly the same! You are falling into the “I don't like the look of that” trap, you may not but it is not dangerous in any way, and if the breaker trips, that is exactly what it is designed to do. I suspect too that Andy J is missing a point, the faster trip time is fairly unlikely as the thermal section is pretty accurate, because it also needs to be very repeatable, and there is no advantage this being quick, although there may be for the magnetic part as contact wear will be reduced. As usual, the question brings up many other pieces of knowledge and information that are largely unconsidered.

It is a good thing you did not have this as a question in your Wiring Regulations exam.

433.1.1 (i) The rated current setting of the protective device (In) is not less than the design current (Ib) of the circuit