Changeover switch

stunlawless · 13 Oct 2009

Morning everyone,

I'm looking for a way to switch an immersion heater from two sources. My first thought is to use a changeover sw to either the heatpump controller or manual switch. I'd hoped to find a double pole 2 way switch that looks a bit like this :

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stunlawless
13 Oct 2009
1

I cant find one; anyone know of a supplier ?

I found plenty of industrial ones like this:

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stunlawless
13 Oct 2009
1

And hager do a nice DIN rail fitted one like this (2pole version is available) :

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stunlawless
13 Oct 2009
1

but neither is exactly what I'm after in the airing cupboard.

Much obliged, David.

The background:

I've just had a GSHP system fitted, giving DHW at 50C, and am in the middle of converting to non-vented DHW, using an OSO 330 litre indirect cylinder. I expected the cylinder to have two immers, but now I realise I misread the spec and only the direct cyls have two fitted.

My plan was to leave one controlled by the GSHP controller (needs to raise the DHW temp to 60C once a week to kill off legionaires disease) and one for manual control to aid recovery time if we have a houseful of guests and all the DHW is used up. I plan to use one of these:

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stunlawless
13 Oct 2009
1

However, as I've only got one immer, then I need to connect it so that I can switch it on independantly of the GSHP.

Immer is a 5kw type, so it has to be switched via a contactor, so the changeover sw won't need a huge rating (1A ?)

londonboy · 13 Oct 2009

I work for a company that installs gshp's.

We use a cylinder stat along with a contactor, this then uses the immersion to top tank upto 60 degrees.

I havent got a wiring diagram but I'm sure you could sus that

stunlawless · 13 Oct 2009

Hello londonboy,

you've described exactly the way the GSHP supplier has wired it.

I'm trying to figure out a way of switching the immer manually from inside the airing cupboard without screwing up the gshp controller, hence the need for somekind of changeover sw.

ColJack · 13 Oct 2009

usually used to control 2 immersions from 1 source ( ie 1 or 2 elements on ) may be able to wire it so that it puts 2 into 1 ?

it would connect the manual to the GSHP though when it was on, but it would disconnect it when off..
is there a problem with back feeding the GSHP's "boost" output?

stunlawless · 13 Oct 2009

Hallo Coljack,

I spotted this MK switch, but, as you say, it would back feed the GSHP when on boost. I don't think that's a good idea, and and if I ask the manufacturer I think I know what the answer will be.

I've already had the GSHP controller replaced under warranty, so I'm nervous about doing anything that might invalidate the warranty.

Conversely, with my changeover sw concept, the GSHP switch line would be unconnected, so if it tried to switch on the immer, no current would flow. That obviously won't cause any physical damage, and I don't think the diagnostic software is clever enough to recognise the lack of current flow, but would pick up the lack of response in water temperature.

I know how to clear that error though, so even if it does happen I won't have to call out the supplier.

Thanks for thinking about the problem, David

ColJack · 13 Oct 2009

I can do you an ugly box to hide and a nice switch on the wall..

RF Lighting · 13 Oct 2009

I think the only way you could do it would be with 2no. two pole contactors.

Could you manage to have a 2 module DIN rail enclosure in the airing cupboard?

ban-all-sheds · 13 Oct 2009

stunlawless said:
And hager do a nice DIN rail fitted one like this (2pole version is available) :

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stunlawless

13 Oct 2009

1

That's a changeover switch?

Where are the other 4 terminals?

matt1e · 13 Oct 2009

not sure if im getting this
does the gshp controller switch on the coil to a contactor? via the cyl stat
and is it the same contactor you want to switch on without back feeding the gshp controller?

matt

stunlawless · 14 Oct 2009

Morning everyone,

@ Coljack: but I don't to go back in the box...

@ BAS: I blew up the picture on Hagers website, and on closer inspection, this is the two pole contactor SF263. I guess the 4 pole version SF463 is actually 8 modules wide, but there's no picture

@ RF: My idea was this:

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stunlawless
14 Oct 2009
1

do you mean this ?

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stunlawless
14 Oct 2009
1

This would fit in a nice enclosure, out of the way of little hands so I like it.

Is it ok to do this ?

@ matt1e: You're spot on, except there is a thermocouple mounted on the cylinder that the GSHP uses to control DHW temp. GSHP would normally control DHW to 50C (max heat pump temp), but once a week will use immer to raise tank to 60C. I intend to keep immer stat in cct, but set at slightly more than 60C so that the GSHP controller doesn't detect a "set temp not reached" error.

When on booster control, the immer stat will control the temperature, and I will fit a mixer valve to ensure that water at the taps, shower etc is never more than 50C.

Of course, the safety cut out will still be there.

If Rob's solution with two contactors in parallel is ok, then I'll go with that. Can't believe it didn't occur to me

Thanks for all your help, David

Ps I know it's all notifiable - completely new floor, non-vented DHW, bathroom electrics

ColJack · 14 Oct 2009

stunlawless said:
This would fit in a nice enclosure, out of the way of little hands so I like it.

that's what I said, I can do you a litte box to hide and a simple switch on the wall...

stunlawless · 14 Oct 2009

Coljack,

Sorry, didn't get your drift. Is the two contacter concept what you were proposing ?

Componded by my bad typing and an attempt at humour...what i meant say was "I don't want to go back in the box". IIRC it was catch phrase of a ventriloquist act when I was a kid. If you remeber it, then you are showing your age.

Thanks, David

ColJack · 14 Oct 2009

yes it was..

stunlawless · 14 Oct 2009

Thanks. I'll get back in my box now...

flameport · 14 Oct 2009

The two contactors solution is by far the best one. Only 1 button for the boost, and no issue of leaving the changeover switch in the boost position by mistake.

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Changeover switch

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