Ufh contactor wiring advice please

[Rockomuir]

Evening all,
Doing a bit of forward planning for an extension with possible electric ufh. i Have worked out room will need 25m2 split between 2 matts 15 and a 10. 150w per square meter matts. I work out as about 16.3 amps in total. Only one stat so a contractorwill have to be fitted.. if Someone could point me in right direction with wiring to include contractor I would be most grateful. Normally I would take supply froom Db to double pole switch to stat then join cold tails and probes. Cannot get my head round contactor tonight. Do I need separate supply’s for stat and contactor, or supply to contactor then to stat via fused spur.
Simple to many I expect . Obviously a 2nd stat negates this problem

 

[TJ Anderson]

You won't necessarily need to have a seperate circuit as the only reason you are using a contactor I assume, is because the switching contacts of your stat are rated less than the connected load you have calculated. You will need a circuit suitable to supply your UFH load plus the negligible power consumption of your electronic stat. A 20A circuit would seem sensible in this case.

Wiring wise you will wire as you would normally but instead of connecting the output of the stat to the cold tails, you connect them to the coil of your contactor (A1 & A2) instead. You then put a supply L&N on one side of the contactor and connect your cold tails on the other side.

 

[Rockomuir]

Thank you, a lot more straight forward than I am making it.

 

[Rockomuir]

I realise contactors can fit in db on din rail or suitable enclosure adj to db. but are there any flush enclosures that are available. Only thing I can think of is a deep fast fix box with a module face plate which does not seem quite right to me.

 

[freddo]

I realise contactors can fit in db on din rail or suitable enclosure adj to db. but are there any flush enclosures that are available. Only thing I can think of is a deep fast fix box with a module face plate which does not seem quite right to me.

Be aware a contactor will clunk loudly every time it operates. A heavy duty relay will operate much more quietly, and be physically smaller too. A mercury displacement relay will operate quieter than the room stat.

 

[James]

Be aware a contactor will clunk loudly every time it operates. A heavy duty relay will operate much more quietly, and be physically smaller too. A mercury displacement relay will operate quieter than the room stat.

Modern solid state relays are silent in operation.
just have to be aware that when they fail, they fail ”closed” so a second method of isolating is important.

 

[freddo]

Modern solid state relays are silent in operation.
just have to be aware that when they fail, they fail ”closed” so a second method of isolating is important.

Yes I've never wanted to use solid state relays where a problem could occur during failure. Difficult fitting an overheat cutout to underfloor heating, though it could be done with thermistors, connected to a thermistor monitoring safety relay controlling a main power contactor. Bit overkill though! That said I abused a modern solid state relay recently, including deliberately shorting the supply across it blowing the 13A supply fuse several times. It's still working. A 16.5A load might require the SS relay to be mounted on a heatsink.

 

[telectrix]

most essential requirement is deep pockets to pay for all that leccy just warming your feet.