Underfloor Heating Using Contactor(s)

[callan]

how do I wire a single phase contactor to underfloor heating? Do I take the load / ie the electrical mat to 2 and 4 and do i take a switch wire to A1 to switch the contactor? and should I locate the contactor(s) next to the consumer unit in a separate box with its own DIN rail?

The house is a large farm house. The floor is Devimat warm Floor System. I've never wired the stuff before. However, after wiring up the Kitchen the Floor Installers asked me to wire it up when they finish laying the floors. Four of the rooms are regular size so I plan using one themostat per room and use a fused switch spur from the ring main.

The fifth room is another story. 60m2 so it will have to be divided into two or three zones. If it's 100W per m2 then 6000W / 230v = 26Amps. That load is too much for the stat to switch (16A max) without contactors.

Do I connect the heating mat supply leads back to a contactor (load side) fitted next to the consumer unit) And do I power the contactor with its own MCB? Or may be I should use two smaller contactors with two separate MCB's?

The other rooms including the kitchen are much smaller so I hope to get away with just using a fused switch spur to supply power.

 

[bugsy]

If your feeding it from a single OCPD fit a contactor for each zone , loop the supply from the OCPD across supply on contactors, wire the load to each zone from the load side of each contactorand control the contactor coil's via the room stat 's this can either be one for each zone or one to control the lot hope it makes sense

 

[callan]

Bugsy,

Thanks for the reply. Yes that's sound advice. I guess a single 32A OCPD looped on the supply end of each contactor will do the trick.

Where should I locate the contactors? Next to the fuse box in their own box? The floor installers seem to think the contactors can be placed in the room zones? To wire up the contactor from the load side of each contactor and control the contactor coil's via the room stat I'd need an 8m 3core cable run from the room stat to the contactors, if located next to the fuse box. That's where the contactors should be located?

What contactors should I use bearing in mind the current load is approx 26A? I found a 24 amp, 4 pole, 230 volt, AC installation contactor but may be this contactor is over sized if I divide the room into 3 zones?

(Used where a single thermostat is required to control a total area of electric underfloor heating exceeding the thermostat loading. Controls up to a maximum of 22K/w (22,000 watts) of heating cable or 96 amps total loading. Designed for domestic applications and DIN rail mounting.
Suitable for housing within a consumer unit or modular enclosure.
DC coil for silent operation)

 

[bugsy]

Hager do a range of modular contactors, use one contactor per zone or group, the stat will only be controlling the contactor coils so there will be no load involved, personally i would install the contactors adj CU

 

[callan]

Bugsy,

Thanks. I assume I could just use one 30A contactor adjacent to the fuse board supplied by a 32A MCB. Then from the load side of the contactor run 2.5 T&E to the floor mat feeds, where the lines and neutrals can be connected together using JB's. This would make the 60m2 room one zone. Is there any reason why this can't be done?

Also, I'll have run a 3 core cable from a 6A MCB to the thermostat, and then connect the switch line of the 3core cable to the contactor coil A1?

Thanks for your advice.

 

[bugsy]

No Worries