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Immersion heater circuit to power underfloor heating


 
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mdrandall

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Joined: 07 Mar 2005
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Location: United Kingdom

PostPosted: Thu Mar 10, 2005 4:39 pm Reply with quote

I have one bathroom which back onto a shower room and at the end of both there is the airing cupboard (if that makes any sense).

I would like to install underfloor heating such as the devimat system and this needs a fused spur and a controller/thermostat outside the bathrooms (e.g. airing cupboard).

In the airing cupboard there is an switch (no fuse) for the 3kW immersion heater which comes off its own circuit from the consumer unit in the garage. Now I never use the immersion heater and would be fairly happy to not have one. But does anyone have any better suggestions???

The Devimat installation data implies up to 16A although I only need 5 sqm for both bathrooms at 100W/sqm. Could I get away with a suitable fcu spur off the immersion heater?

Alternatively, could I install a multi-pole switch such that the circuit powered either the immersion or the underfloor heating?

Thanks in advance.
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kai

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PostPosted: Thu Mar 10, 2005 10:46 pm Reply with quote

It seems you are trying to install something covered by Part P (underfloor heating), have you submitted the Building Notice Form yet to the Council?

The Immersion circuit may not be to current standards (i.e. no fuse), worth getting it's wiring checked out professionally first.
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felix

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PostPosted: Thu Mar 10, 2005 11:17 pm Reply with quote

You say that the immersion heater has its own fuse in the consumer unit (which is a common arrangement). What size fuse is it?
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securespark

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PostPosted: Thu Mar 10, 2005 11:46 pm Reply with quote

Part P aside, you can run a system such as yours from a fused spur, so yes, you can run it off an immersion circuit, with a couple of mods.

You need to check that the circuit is capable of supplying 13A (if run in 2.5 with a 15/16A fuse/breaker this should suffice).

Then you need to replace the 20A DP switch for a switched fused spur.

Then you need to protect the circuit with an RCD, if not already. These last two you can kill with one stone by using a Powerbreaker H92 RCD spur or similar.

The system I installed was WarmUp, and that too had a potential max of 16A, but that was just the rating of the control unit. In my install., I had two coils for a bahroom about 8' x 10', and in the H92 I put a 5A fuse.
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mdrandall

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PostPosted: Fri Mar 11, 2005 7:17 am Reply with quote

Thanks guys. The house is less than 1 year old so I expect it conforms to all the latest regs. It certainly appears to be 2.5 wire into the immersion switch. Do I really need to fill in a building notice form for underfloor heating seeing as they sell the kits in the "sheds"?

Is the rcd fused spur you refer to like this

http://www.tlc-direct.co.uk/Products/BRH92.html

Securespark....you seem to be suggesting not having the immersion anymore as you have one rcd fused spur with a 5a fuse. Is that correct?

Sorry to be a bit slow........................
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ban-all-sheds

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PostPosted: Fri Mar 11, 2005 10:40 am Reply with quote

securespark wrote:
These last two you can kill with one stone by using a Powerbreaker H92 RCD spur or similar.

The H92 is unswitched. Is tripping the RCD via the test button an acceptable means of isolation?
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Adam_151

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PostPosted: Fri Mar 11, 2005 10:43 am Reply with quote

ban-all-sheds wrote:
securespark wrote:
These last two you can kill with one stone by using a Powerbreaker H92 RCD spur or similar.

The H92 is unswitched. Is tripping the RCD via the test button an acceptable means of isolation?


I would think that if it was double pole (I would imagine an RCD would break two poles), and the contact gap was 3mm or more (how you would find this out I don't know?) then I can't think of any reason why it wouldn't be acceptable
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ban-all-sheds

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PostPosted: Fri Mar 11, 2005 10:44 am Reply with quote

mdrandall wrote:
Do I really need to fill in a building notice form for underfloor heating seeing as they sell the kits in the "sheds"?

When did you move in to the house? If you started the work last year, and you finish it before the end of this month then you are exempt from the new building regs. Otherwise, legally, yes you do have to notify them, or employ an electrician who can self-certify Building Regulations compliance... icon_sad.gif
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mdrandall

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PostPosted: Fri Mar 11, 2005 8:14 pm Reply with quote

Well I have sort of started work already as I have run the cold wires from the heating mat from the nathrooms into the airing cupboard. It's just the final connection to the supply that needs to be done.

Still would like to find a 20A DP change-over switch so that I can select either the immersion heater (only if the gas boiler/pump fails) or the under floor heating via the rcd fcu as advised.
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securespark

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PostPosted: Fri Mar 11, 2005 11:21 pm Reply with quote

Sorry, I was under the impression you were ditching the immersion heater.

If the IH is 3kW, then I suppose you could create a 20A radial, and run the supply for the UFH off it.
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mdrandall

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PostPosted: Sat Mar 12, 2005 3:32 pm Reply with quote

Thanks again Securespark. I will probably end up ditching the immersion heater but my better half is concerned that we will not have any hot water should the boiler fail. I tried to explain the chances of that are slim but ......

I think a 20A radial idea is best, thanks again.
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plugwash

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PostPosted: Sat Mar 12, 2005 3:46 pm Reply with quote

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mdrandall

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PostPosted: Sat Mar 12, 2005 8:02 pm Reply with quote

That's exactly the sort of thing I need. I can keep the immersion heater on one side of the switch and the new fused rcu for the floor heating on the other side.

Thanks very much
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