Under floor heating mat 15Amps

Kinxsize · Sep 29, 2023

Hi there
I need your opinion on this one, I need to fix mat 18sqm (200w). Client instead of one mat bought 2 mats (12sqm)+(6sqm) one thermostat . Went through the manual of under floor heating so 12sqm (2400w) + 6sqm(1200w) total 3600w.
Now my question, how do I spur nearly 16amps, standard spur comes up to 13amps. Those 2 mats can be on one thermostat up to 16 amps anything above that need to be on contractor .
Is there any way to get that connected on switch spur? Or the only way is to split those 2 mats add another supply and thermostat for it?
Did you ever had such a situation?
Thanks for any reply.

DefyG · Sep 29, 2023

Is there a convenient place to install a small enclosure with a DP 16A mcb on the RFC?

westward10 · Sep 29, 2023

You don't spur from a ring final for a 3.6kw load, you install a separate circuit.

Taylortwocities · Sep 29, 2023

Kinxsize said:
I need your opinion on this one, I need to fix mat 18sqm (200w). Client instead of one mat bought 2 mats (12sqm)+(6sqm) one thermostat . Went through the manual of under floor heating so 12sqm (2400w) + 6sqm(1200w) total 3600w.

I do not understand your maths. The 200watts is per square metre. So the original 18sqm mat would be 3600watts. The mats the client has bought will also be exactly the same at 3600watts.
In both cases you will need a separate circuit, (16amp minimum) and you need to make sure that the thermostat/programmer and any switches are capable of a load of that size.

Kinxsize · Sep 30, 2023

westward10 said:
You don't spur from a ring final for a 3.6kw load, you install a separate circuit.

Yes I do have dedicated circuit for under floor heating.

Kinxsize · Sep 30, 2023

Taylortwocities said:
I do not understand your maths. The 200watts is per square metre. So the original 18sqm mat would be 3600watts. The mats the client has bought will also be exactly the same at 3600watts.
In both cases you will need a separate circuit, (16amp minimum) and you need to make sure that the thermostat/programmer and any switches are capable of a load of that size.

Hi maybe I have ask wrong question. I do have dedicated cable for under floor heating and it will be on 20 amp rcbo but the question is you got to have switch spur to isolate it before its power thermostat. How do I do the spur when the load is over 13 Amps? ( double pool isolator 20amp? )

Taylortwocities · Sep 30, 2023

Kinxsize said:
Hi maybe I have ask wrong question. I do have dedicated cable for under floor heating and it will be on 20 amp rcbo but the question is you got to have switch spur to isolate it before its power thermostat. How do I do the spur when the load is over 13 Amps? ( double pool isolator 20amp? )

Your dedicated circuit is a radial, so a connection to a radial is just part of the radial, it's often called a branch.
The term "spur" is when a single cable connection is made to a ring final circuit.
It's important terminology as the branch you are making from the radial does not need a fused connection unit (you would if you were spurring from a ring).

You do need to be able to isolate the UFH from the radial so, yes, a 20amp Double pole switch is the way to do it. Current on the radial is limited by the 20A RCBO.