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Topic Title: Underfloor heating >16amp & contactor
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Created On: 22 March 2013 10:43 AM
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 22 March 2013 10:43 AM
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truss

Posts: 1250
Joined: 27 March 2005

Hello all,

Haven't been here for ages...have you missed me?

I've installed a dedicated 20amp supply for UFH and the client only wants one thermostat.

2.5 T&E run from DB to flush single box for 20A DP switch then 2.5 up to another flush single box for stat with 20mm conduit run back down the wall for heating mat tails & stat cable.

Floor size is roughly 28m2 and mat is to be 150W per SqM

I'm aware that I need to fit a contactor but can't get my head around how to do this (I'm just a humble housebasher you see & contactors confuse me a bit )

Ideally, I would like to fit the contactor on a din rail at the DB or in a separate enclosure adjacent to it but am thinking that the heating mat tails need to go to the contactor.

Would someone be kind enough to hold my hand and walk me through this?

Thanks
 22 March 2013 11:07 AM
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AJJewsbury

Posts: 11545
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Can you get it down to about 24.5m²? - that way the load would be 16A and you can use a normal 16A UFH thermostat.

If you want the contactor back at the CU, you'll need an couple of extra cores at least between the thermostat and the CU.

Otherwise a wireless 'stat comes to mind.

- Andy.
 22 March 2013 11:26 AM
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truss

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Hi Andy

To be honest 28m2 (how do you do the small 2s BTW?) is a bit of a guesstimate...I'm going back to site this afternoon & will have a proper measure up.

Didn't think of a wireless stat...not sure how that would work with UFH?

Assuming a contactor is definitely required & a wireless stat is out of the equation...would this be the correct sequence?

2.5 from board to 20A DP isolator to contactor...UFH tails also to contactor...1.0 from contactor to stat...stat probe cable from stat to floor

Also, would the contactor have to be supplied seperately on it's own 6amp circuit?

Thanks mate
 22 March 2013 12:06 PM
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Parsley

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Not sure exactly what system who have but I would use the stat output that would normal go to the UFH cold tails to switch the contactor on/off. You will need a permanent feed to the stat you could supply that off a different circuit if you want or use the 20Amp supply to the UFH and fuse it down if it's really neccessary can a stat overload? If the contactor has two supplies one for the load and one for the coil install a warning label. The supply to the UFH is then suppled directly from the consumer unit via the contactor and local connection unit for the UFH cold tails and is switched on/off from the stat.

Regards
 22 March 2013 12:10 PM
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AJJewsbury

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how do you do the small 2s BTW?

I'm lazy so I just paste it in from word! I think there's an alt-sequence that'll do it too (someone will know off the top of their head).

Didn't think of a wireless stat...not sure how that would work with UFH?

Usually they come in two parts - battery powered 'stat you can fix where you like (no wiring required) and the mains powered receiver that provides a switched output - stick that next to the CU and use the output to switch your contactor.

Assuming a contactor is definitely required & a wireless stat is out of the equation...would this be the correct sequence?

2.5 from board to 20A DP isolator to contactor...UFH tails also to contactor...1.0 from contactor to stat...stat probe cable from stat to floor


A mains powered 'stat will need a permanent L, usually a N as well and provides a switched L (which you use to supply the contactor coil of course). Other side of the contactor coil connected to N of the same circuit. So if the contactor is at the CU then you might need a 3 core + E to the 'stat.

I don't see a problem having the contactor before the isolator - which is probably more convenient if the contactor is in the CU. Do you even need a separate isolator anyway? Won't the MCB do? (unless TT or manufacturer's instructions say otherwise of course.)

Also, would the contactor have to be supplied seperately on it's own 6amp circuit?

Depends on what the 'stat manufacturer says - but probably more convenient to do so - if only because you can then have smaller conductors to the 'stat without worrying.

- Andy.
 22 March 2013 12:39 PM
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Zs

Posts: 2964
Joined: 20 July 2006

Worry not Truss. I have the same T shirt as the one you will soon be getting.

Here is a useful number for you:

WarmUp Technical: 08453 452288

They will walk you through the process and will email you a detailed wiring diagram. If you are not using a warmup system then perhaps don't tell them that They are all pretty much the same.

And oh, don't worry about the 'snubbers' they talk about. I got very confused by all that and did not need them on a system very similar to the one you are describing.

It works.

Zs
 22 March 2013 01:42 PM
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Avatar for truss.
truss

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Joined: 27 March 2005

Thanks Parsley, Andy & Zs

Originally posted by: AJJewsbury


Usually they come in two parts - battery powered 'stat you can fix where you like (no wiring required) and the mains powered receiver that provides a switched output - stick that next to the CU and use the output to switch your contactor.


The only problem i see with this is not having anywhere to terminate the floor temperature probe

Originally posted by: Zs

Worry not Truss. I have the same T shirt as the one you will soon be getting.


lol you mean this one?



Here is a useful number for you:

WarmUp Technical: 08453 452288


Thanks for that Zs, will give them a call

But before i do, here's my take on it...



Does that look about right?
 22 March 2013 01:55 PM
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AJJewsbury

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The only problem i see with this is not having anywhere to terminate the floor temperature probe

It would connect to the 'stat as normal - e.g. http://www.heatmisershop.co.uk...heating-thermostat-p80 (I should have said no mains wiring required at the wireless end).

But before i do, here's my take on it...

Looks reasonable. I don't think the stats are usually DP switching, but that makes little difference.

Another option instead of a FCU is to use another MCB in the CU - might be neater/cheaper.

- Andy.
 22 March 2013 02:12 PM
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Avatar for truss.
truss

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Joined: 27 March 2005

Originally posted by: AJJewsbury

It would connect to the 'stat as normal - e.g. http://www.heatmisershop.co.uk...heating-thermostat-p80 (I should have said no mains wiring required at the wireless end).


That's the kiddie...that wireless stat will get me out of trouble with the builder - thanks Andy
 22 March 2013 03:00 PM
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Zs

Posts: 2964
Joined: 20 July 2006

Andy....I want that T shirt for wearing to the office.

LMSO. S=Socks cos I am being polite today.

Zs
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