Immersion heater - remote control

[Bill]

Amongst all the other projects both sons have got me "helping with", we have an immersion heater.

He has an iphone and can switch various things on and off remotely. Apparently the house controller has switched contacts labelled "Immersion Heater" so he wired these to the immersion heater.

It worked for about a day. He then read the instructions and saw the heater was rated at 13A and the switch contacts in the controller at 3A.

He has asked me what sort of relay he needs to install next to the HW tank.

I have suggested

Is this OK? Are there likely to be heat problems with the box he mounts it in? I have suggested stranded wire via a choc block if the existing cable is solid core, crimped terminals and a decent, earthed metal box.

I don't think it would be easy to cable a controller output to the main distribution board, but would a "proper" way to do it be to fit some sort of relay/actuator in that in the supply to the immersion?

[Fredxxx]

The relay is rated at 70degsC ambient. I would say it is fine as long as its not in contact with a hot pipe or the hot tank.

It looks a little expensive to me as it's a 2 pole, 2 throw relay. You only need a single pole single throw SPST N/O relay.

Or plastic box that wouldn't need earthing?

I don't see the issue, just place a relay in the same location as the controller and use the relay to switch the live to the immersion heater.

[Bill]

In message , Fredxxx writes

It won't be in contact with the tank or hot pipework, but will be in his big, room sized airing cupboard. So a moderately high ambient temperature and possible heat transmission down the cable from the immersion. We just want to be sure, as it's all being turned on when the house is empty.

The relay needs to be at the heater end of the cable from the controller. I can't supervise or do any more decorative work in the hall where the controller is.

I was told that it had to switch live and neutral to be legal. There are cheaper, similar relays available online, and a 30A dpdt mains driven relay seems to be a standard type. There are solid state relays that are single pole, but I'm not sure about heat dissipation (some seem to have heatsinks), and they are more expensive.

I might look up the temperature ratings of plastic boxes.

Thanks.

[jrwalliker]

I can't think of any reason for needing a double pole relay. Double pole contacts are only needed for an isolator and a conventional or solid-state relay would not be acceptable for isolation anyway.

Have you considered what would happen if the water supply is shut off when the occupier is away and the immersion heater is switched on remotely?

John

[DerbyBorn]

[e-mail] wrote in news: [e-mail]:

Probably no worse that other cicumstances where water could go off during the nigh and perhaps a washer was working. Ensure the immersion is a recent one with a thermal cutout. (I guess)

[Fredxxx]

Most light switches are single pole for example.

I think it would have some fuseable safety feature if it ran dry though that's not likely to happen with a HW cyclinder as it will always contain water unless specially drained.

One would hope there is still an immersion isolation switch somewhere!

[ARW]

A cylinder full of of water?

[Tim Watts]

Me neither. Switching does not need double pole. There'd be an isolator before the relay anyway and that can be DP.

Hopefully nothing unless the tank is drained down? And failing that, the immersion *should* have a failsafe trip built in - but I'm not sure if that's a mandatory requirement or just a feature of better heaters.

But part of a "going away lockdown" would include turning the local isolator off if turning the main water off.

BTW for the OP - you can get DIN rail contactors (fancy name for a relay) if you want to make the job look solid. Some contactors include a local override lever, which could be a useful feature. Or wire a 20A switch in parallel.