Underfloor Heating

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Buckinghamshire
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Hi

I am installing Underfloor Heating approx 18m2 @200w/m. I have a dedicated feed available(rcd protected) From The CU. Can someone please advise

1/ Do I need an FCU between the feed from the CU and the thermostat?

2/ If so what size fuse should I use?

3/ what size mcb at the CU?

4/ What size cable from the CU to the FCU?

5/ What size cable from the FCU to the thermostat. Flooring uses 1.5mm2?

PS I know I need to notify the local Authority.


Any advice much appreciated.



Thanks
 
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When you say 18M², do you mean 4.25 x 4.25 or do you mean 18 x 18?
Also, the load @ 200w/m will depend on the total length, which also depends on the spacing, so as to know how many runs you'll have. If you see what I mean.
 
Sorry I mean 4.25x4.25..Its underfloor matting and the manufacturers are quoting 200 watts per sq metre output...is this enough info?

Thanks
 
On that basis you're looking at 16A or 3.68kW.
Therefore a 13A FCU would be no use.

I haven't done u/f heating as yet, but I understand you might need to use a contactor instead of 20A MCB. I am sure there must be others on this forum with the necessary experience and expertise to advise you better.

As regards cable size, you could just about get away with 1.5mm², depending on the length, but I'd be inclined to play safe and use 2.5mm². HTH
 
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Thankyou...I think your probably right...I'm gonna go the contactor route, cover all the bases that way. Unless anyone thinks this is OTT

Thanks
 
You'll still need your 20A MCB, but the contactor (say a 20A SP contactor) will fit between your CU and thermostat. Sorry I hope I haven't confused you here.
Also it needs to be RCD protected.
 
Thanks. you have n't confused me, youve actually made my decision for me. 20a mcb feeding 20a 2 pole contacter ,rcd protected.


Cheers
 
Why are you using a contactor????

Normally (if powering from a RCD protected ring) you install a FCU with a 13A fuse, then you connect that to the UFH controller (could use 1.5 T&E). The cold heating tails and thermostat probe then connect to the controller usilg the supplied cable.

If you had a dedicated circuit for this I would use a 16A MCB and a DP Isolator instead of the FCU.
 
The thermostat is only rated at 16 amps, the way you are suggesting was how I was goin to do it originally but I was concerned that the thermostat rating would be exceded???

Would the DP switch be 20A ???

Thanks
 

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