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 http://uk.rs-online.com/web/p/products/4927202/

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?


--
Bill

On 23/08/2015 15:34, Bill wrote:
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 http://uk.rs-online.com/web/p/products/4927202/

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.

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.

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?

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.

In message , Fredxxx
writes

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.

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?

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.

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.
--
Bill

On Sunday, 23 August 2015 17:53:01 UTC+1, Bill wrote:

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 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

wrote in
:

On Sunday, 23 August 2015 17:53:01 UTC+1, Bill wrote:

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 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


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)

On 23/08/2015 18:19, wrote:
On Sunday, 23 August 2015 17:53:01 UTC+1, Bill wrote:

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 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.

Most light switches are single pole for example.

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?

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!

wrote in message
...
On Sunday, 23 August 2015 17:53:01 UTC+1, Bill wrote:

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 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?


A cylinder full of of water?

--
Adam

On 23/08/15 18:19, wrote:
On Sunday, 23 August 2015 17:53:01 UTC+1, Bill wrote:

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 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.

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

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?

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.