Discuss under floor heating 32amp final ring advice needed in the Electrical Appliances Forum area at ElectriciansForums.net

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kimeddie

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Hi all

looking for some advice as a non sparky , be gentle :) To be clear I wont be doing the work myself , just want to be better informed.

I already had an underfloor heating mat rated at 6.8A installed in my kitchen , this worked off a fused spur (13A) on the kitchens 32amp Ring final circuit for years.
My builder installed another mat rated at 10.65A (when we retiled) and tried to wire it in to the same thermostat (on the existing fused spur) , he then realised that wasn’t going to work as the 2 matts combined to 17.45A (more than what the fused spur can handle or the thermostat)
Given his mistake I want to be better informed when he tries to fix it as hes tried to cut corners a few times on me now.
So options wise what do you think is best? , remembering the UFH cables can’t move too much from their current location + the walls have all been decorated and the tiling completed :)
-add an additional 13amp spur off the ring final right next to the current one and use that for the 2nd mat ? (i can get an additional controller)
-remove the fused spur and extend the final ring past the existing fused spur into the 2 thermostats directly
-run a new cable from the consumer unit (reluctant given the rooms have been decorated now and I don’t think it’s a stud wall rather brick )
-install a contactor snubber (requiring a big bulky box on the kitchen wall )
I’d also note on the same ring final I have a kettle , toaster, microwave , air fryer never y all used at the same time though of course (+ cooker on its own circuit). I guess the key is will the 2 matts really pull 17.45A collectively all that often ? Its annoying that they total 16 amps as then I could connect to 1 thermostat (warmup) without a contactor.
fyi It looks like the fused spur is 2.5m cable

Apologies if any of the both is stupid or dangerous , i probaaly know a dangerous amount (a bit but not enough ) that why im on this forum to learn 😊 and to reiterate I wont do any of the work myself just want the collective advice from you all before I agree to let my electrician do the work

Thanks !
 
I personally would be putting the underfloor heating on its own circuit. 1 spur off a ring for ufh….maybe. But 2…not so sure. I would bear in mind and I could be wrong but diversity should not be applied when it comes to ufh mats. So if that’s the case then the load of the 2 ufh mats will be utilising 50% of your kitchen ring final circuit. Also you need to confirm that the builder is altering the circuit correctly. Has he carried out appropriate tests? Etc
 
-add an additional 13amp spur off the ring final right next to the current one and use that for the 2nd mat ? (i can get an additional controller)

This is unwise, significant heating loads shouldn't be fed from a ring circuit. Loads should be evenly distributed around a ring circuit and adding nearly 18A to a single location doesn't achieve this.
Also this will use up most of the capacity of the circuit and leave it prone to small overloads (dangerous) or nuisance tripping.

-remove the fused spur and extend the final ring past the existing fused spur into the 2 thermostats directly

No, absolutely not, that has the potential to become a dangerous situation or a fire.

-run a new cable from the consumer unit (reluctant given the rooms have been decorated now and I don’t think it’s a stud wall rather brick )

This is the best option, significant heating loads should really be fed from dedicated circuits.
-install a contactor snubber (requiring a big bulky box on the kitchen wall )

A contactor could be used to control both mats from the one thermostat, it doesn't have to be installed on the kitchen wall though.

Your ideal soloution here would be a new 20A circuit to feed both mats, with a contactor installed in a suitable location (it could be at the origin of the circuit, or even in the CU if there is space) and controlled by the thermostat.
This would require a new circuit being run to the mats and a cable from the thermostat to the contactor.

I guess the key is will the 2 matts really pull 17.45A collectively all that often ?

If controlled by the same thermostat yes they will, they will draw either 17.45A or 0A depending in whether the stat is on or off.

fyi It looks like the fused spur is 2.5m cable

Is it just one 2.5mm cable or 2 feeding the switchfuse?
 
This is unwise, significant heating loads shouldn't be fed from a ring circuit. Loads should be evenly distributed around a ring circuit and adding nearly 18A to a single location doesn't achieve this.
Also this will use up most of the capacity of the circuit and leave it prone to small overloads (dangerous) or nuisance tripping.



No, absolutely not, that has the potential to become a dangerous situation or a fire.



This is the best option, significant heating loads should really be fed from dedicated circuits.


A contactor could be used to control both mats from the one thermostat, it doesn't have to be installed on the kitchen wall though.

Your ideal soloution here would be a new 20A circuit to feed both mats, with a contactor installed in a suitable location (it could be at the origin of the circuit, or even in the CU if there is space) and controlled by the thermostat.
This would require a new circuit being run to the mats and a cable from the thermostat to the contactor.



If controlled by the same thermostat yes they will, they will draw either 17.45A or 0A depending in whether the stat is on or off.



Is it just one 2.5mm cable or 2 feeding the switchfuse?
Tha KS
I personally would be putting the underfloor heating on its own circuit. 1 spur off a ring for ufh….maybe. But 2…not so sure. I would bear in mind and I could be wrong but diversity should not be applied when it comes to ufh mats. So if that’s the case then the load of the 2 ufh mats will be utilising 50% of your kitchen ring final circuit. Also you need to confirm that the builder is altering the circuit correctly. Has he carried out appropriate tests? Etc
Thanks for the advice
 
This is unwise, significant heating loads shouldn't be fed from a ring circuit. Loads should be evenly distributed around a ring circuit and adding nearly 18A to a single location doesn't achieve this.
Also this will use up most of the capacity of the circuit and leave it prone to small overloads (dangerous) or nuisance tripping.



No, absolutely not, that has the potential to become a dangerous situation or a fire.



This is the best option, significant heating loads should really be fed from dedicated circuits.


A contactor could be used to control both mats from the one thermostat, it doesn't have to be installed on the kitchen wall though.

Your ideal soloution here would be a new 20A circuit to feed both mats, with a contactor installed in a suitable location (it could be at the origin of the circuit, or even in the CU if there is space) and controlled by the thermostat.
This would require a new circuit being run to the mats and a cable from the thermostat to the contactor.



If controlled by the same thermostat yes they will, they will draw either 17.45A or 0A depending in whether the stat is on or off.



Is it just one 2.5mm cable or 2 feeding the switc
 
This is unwise, significant heating loads shouldn't be fed from a ring circuit. Loads should be evenly distributed around a ring circuit and adding nearly 18A to a single location doesn't achieve this.
Also this will use up most of the capacity of the circuit and leave it prone to small overloads (dangerous) or nuisance tripping.



No, absolutely not, that has the potential to become a dangerous situation or a fire.



This is the best option, significant heating loads should really be fed from dedicated circuits.


A contactor could be used to control both mats from the one thermostat, it doesn't have to be installed on the kitchen wall though.

Your ideal soloution here would be a new 20A circuit to feed both mats, with a contactor installed in a suitable location (it could be at the origin of the circuit, or even in the CU if there is space) and controlled by the thermostat.
This would require a new circuit being run to the mats and a cable from the thermostat to the contactor.



If controlled by the same thermostat yes they will, they will draw either 17.45A or 0A depending in whether the stat is on or off.



Is it just one 2.5mm cable or 2 feeding the switchfuse?
Thanks for the comprehensive advice. I think I'll bite the bullet and get a new wire installed and redecorate that wall.
Re your question I think it's a two 2,5 wires feeding the spur, IE either end of the ring connection.
 
I do agree with everything that have been said above. Of course the best option is to have it on dedicated circuit, but it's 32A ring final. Would you ruin walls in your own homes just to have it on separate circuit? (I know you wouldn't be silly enough not to do that this way in the first place). If everything is done properly overload will never occur as circuit is protected by suitable breaker.
Nuisance tripping? I don't really see kimeddie reaching 32A.

I'm more interested in your opinions than trying to convince anybody to anything.
 
I do agree with everything that have been said above. Of course the best option is to have it on dedicated circuit, but it's 32A ring final. Would you ruin walls in your own homes just to have it on separate circuit? (I know you wouldn't be silly enough not to do that this way in the first place). If everything is done properly overload will never occur as circuit is protected by suitable breaker.
Nuisance tripping? I don't really see kimeddie reaching 32A.

I'm more interested in your opinions than trying to convince anybody to anything.
@tolklu This is perhaps a thread that should have been created in the Electricians Arms to discuss, rather than here. Remember overloads are still possible in Ring circuits where loads aren’t evenly distributed. We wouldn’t want to give conflicting advice or what could be confused as conflicting advice.


@kimeddie The wiring regs are very clear on this situation. Appx 15 has a standard ring circuit layout in which it says fixed loads of 2kW or higher should not be fed from a ring circuit.
Best practice really would be to run in a dedicated circuit for the underfloor heating.
Whilst technically the original mat will be fine the new mat (10 amp) will be over the 2kW rating.
 

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