On 17/12/16 00:08, Bill wrote:
Son's house is wired so he can, via his iPhone and home wifi, control
his central heating etc. etc. from the train.
Not sure what system, but it has a controller for the heating and a
separate controller for the immersion.
The heating is OK, but he didn't read the spec and the immersion took so
much current that the controller died.
He has now, with some drawings from me, wired in a 30A rated relay with
230v ac coil. I bought him a box to mount it in, but it apparently isn't
decorative enough for his walk-in airing cupboard, so as a very
temporary measure he has wired it all up al fresco via the old immersion
isolator switch.
He reports that it all works well except for the buzzing from the relay
coil, which is bound to get louder when it's mounted in a box on the wall.

I have said I'll ask around to see if anyone knows whether all this type
of relay is noisy, or whether anyone knows how to select a silent type.

I decent relay should not be obviously noisy. Try an Omron brand from
RS/Farnell.

His immersion needs a relay capable of handling 13A resistive load AC at
mains voltage with a 230-250VAC coil.