40A switch on a 63A circuit

[telnet]

Hi, I would be grateful for an opinion from someone in the know: I had an electric shower fitted by a firm of electricians. They took a cable from the old style fuse box and into a 63A circuit breaker with a 30 mA RCD. So far so good. The cable runs to a twin pole isolator pull cord switch in the bathroom ceiling, and from there to the shower.

I wanted a spur to a convector heater, which I took from the shower side of the isolator switch. I calculated that the shower and the heater together would draw 48A. I assumed that this would be fine on a 63A circuit.

The system worked for about 6 months and then I lost power to the shower and the heater. The circuit breaker had not tripped. I then discovered that the isolator was rated to only 40A and the contacts had been burned out by the 48A load.

My question is whether a 40A switch on a 63A circuit conforms to Chapter 17? Or was it my fault for not considering the load on the switch?

 

[ericmark]

The rules say where the appliance uses more than 2kW it should have a dedicated supply. Also by altering a circuit the onus in on you to ensure the supply is suitable. So although one would not normally use a 40A on a 63A auto disconnection device once you altered the circuit that was up to you to ensure it was correct.

What is more to point is for 63A even clipped direct you would need 10mm sq cable and for in a wall even 16mm sq would not always be big enough. To fit 16mm sq cable into a 40A pull switch would not be easy.

So likely the error is there should not be a 63A MCB and I have not seem any miniature automatic disconnection units of 63A normally a full size moulder breaker is needed for that size. I would think it should have been a 40A MCB not 63A.

 

[EFLImpudence]

These switches (usually 45A ?) frequently suffer from overheating because of loose connections so may have been a coincidence but with 48A not surprising.

Having said that, it should not be on a 63A circuit so the wrong MCB was fitted.

Having said that, with, say, a 40A shower it could not have been overloaded - and, presumably wasn't, until you came along.

 

[westie101]

Or is it just a 63A RCD with no overload protection? This has been seen before

 

[EFLImpudence]

Or is it just a 63A RCD with no overload protection? This has been seen before

That's a good point.

Wrong description from OP?

 

[DetlefSchmitz]

Very probably - a photo would be good.

 

[securespark]

We like photos.