Under floor heating

MATTMGM · Dec 30, 2015

Hi guys,

after some advice please.

Been asked to install electrics for an underfloor heating system that consists of 3 x 10m2 mats, at a maximum rating of 2400 watts per mat, ran off the one thermostat (max 16amps).

Has anybody ever wired this system using a 40amp contactor?? And if so all help would be gratefully appreciated. (diagrams)

thanks

kenny7askew · Dec 30, 2015

pretty straightforward,the thermostat switches the contactor coil on and the contactor contacts switch the power to the mats

MATTMGM · Dec 30, 2015

Thanks,

Would i be correct in saying i would supply the contractor with a 10mm2 cable. then supply the 3 individual mats with a 2.5mm t&e and joint in a junction box.

Octopus · Dec 30, 2015

out of interest where do you plan to "conceal" the contactor and the cables? Last one I saw like this the contactor was in a 47mm deep back box, mounted "portrait", behind a 2G blank! A right dogs dinner!

davesparks · Dec 30, 2015

MATTMGM said:
Thanks,

Would i be correct in saying i would supply the contractor with a 10mm2 cable. then supply the 3 individual mats with a 2.5mm t&e and joint in a junction box.

No you wouldn't be correct! The 2.5 would then not be protected.

The last time I did this I ran 3x 10A circuits switched with a 3 pole contactor.

dansk · Dec 30, 2015

Have a long hard think about what contractor your using and where it's going to be positioned, if it's not going to be out of ear shot of the home owner consider a silent switching one to lower the chance of having to move it. What may seem quite during the day can be very loud at night when the heating is switching on and off.

Deleted member 9648 · Dec 30, 2015

davesparks said:
No you wouldn't be correct! The 2.5 would then not be protected.

The last time I did this I ran 3x 10A circuits switched with a 3 pole contactor.

Same arrangement last time I did one.

Post #3 is a worry.

Also worth pointing out to the end user just how much this will cost to run per hour.

Lagentium · Dec 31, 2015

Worth considering the length of the tail to the mat to be able to have everything concealed but also not not making anything inaccessible, because if it's just 3 x mats laid down then they will all have their own individual supply and they will all be at different points within the room, check with manufacturers instructions that they can be ran via a stat controlling a contactor, the ones I've done in the past have a stat in the floor and run via a controller that has the stat input and mat output in it.

davesparks · Dec 31, 2015

Lagentium said:
Worth considering the length of the tail to the mat to be able to have everything concealed but also not not making anything inaccessible, because if it's just 3 x mats laid down then they will all have their own individual supply and they will all be at different points within the room, check with manufacturers instructions that they can be ran via a stat controlling a contactor, the ones I've done in the past have a stat in the floor and run via a controller that has the stat input and mat output in it.

Of course it can be run via a contactor, its no different to connecting it directly to the stat!

Lagentium · Jan 1, 2016

I understand that, but manufacturers instructions need to be complied with for warranties etc!

davesparks · Jan 1, 2016

Lagentium said:
I understand that, but manufacturers instructions need to be complied with for warranties etc!

How on earth would this have any effect on the warranty?

Lagentium · Jan 1, 2016

If the installation isn't installed as per the manufacturers say it should be, if they send a rep out and it differs from the instructions and there is a problem they will probably wash their hands, I've seen it happen, that's why I commented about it. But, crack on and install things as you want as it's just my opinion!

davesparks · Jan 1, 2016

Lagentium said:
If the installation isn't installed as per the manufacturers say it should be, if they send a rep out and it differs from the instructions and there is a problem they will probably wash their hands, I've seen it happen, that's why I commented about it. But, crack on and install things as you want as it's just my opinion!

What on earth is a rep going to know?

Which underfloor heating manufacturer was it when you saw it happen?
They would have to be able to prove that whatever fault has occurred could be due to the deviation from their instructions, and there's no way adding a contactor could do that. It's far more likely that the manufacturer would bull**** their way out of it by baffling a customer who is too daft to think for themselves with that nonsense.