Large load UFH

[Dunc]

Doing a kitchen job at the moment and as is the norm electric under tile heating has been specified throughout the tiled areas. Being a big area the load (about 4kW) is greater then the stat can handle so i'm going to have to fit a relay or contactor in line with the load.

Firstly, does anyone know whether or not the stat has a double pole or single pole relay fitted inside it. The reason i ask is because i wander if the load has to have double pole switching as it will then have a bearing on what device i can fit to control the load.

I'm trying to stay away from contactors as i have known them to effect the operation of the stat due to transient voltages generated during operation. I know that a snubber can be fitted to eleviate this problem but the contactors are also inherently noisy and due to the spec of the kitchen and the proximity of the contactor location to the main circulation area of the house i don't think a chuffing great 'clonk' sound will be acceptable several dozen times a day.

So i was wandering about the possibility of using a solid state relay as found in air con units and similar refrigeration items. I've found one here that would appear to tick the boxes and with it being a solid state relay should ensure trouble free (and quiet) operation for many years over a contactors moving parts. My only slight concern is that it is single pole but personally i don't see this to be an issue with so many stats in electrical heaters being single pole (eg immersion heaters).

Your thoughts would be gratefully received (so long as they're nothing to do with running costs of such a rubbish system, i'm only the installer after all! ).

 

[malcolmsanford]

Did it not come as a kit ?? I would have thought that now with the profusion of these systems you could get a suitably rated thermostat for it.

 

[telectrix]

for such a large area , i would have thought more than 1 stat.

 

[Dunc]

Did it not come as a kit ?? I would have thought that now with the profusion of these systems you could get a suitably rated thermostat for it.

It came as multiple kits, 3 rolls of mat and a thermostat. The third mat kit was supplied last as the kitchen company didn't do there measurements correctly. As usual it's a case of someone bought the gear and i'm expected to make it work without it going faulty within 365 days! I'm guessing the full final load slightly as no one can tell me the exact load of the final kit (all boxes were chucked by the time i arrived back on site and the invoices the kitchen company have aren't clear) but by measuring the resistance and doing a quick calc i make it to be about 700W plus the 3kW that i know is already in. The existing stat is rated at 3.6kW but the idea of forcing 2x 2.5mm cables in to a. the back box and b. the terminals without damaging anything isn't my idea of fun especially when there is no guarantee it will actually work for a sustained period of time.

 

[Dunc]

for such a large area , i would have thought more than 1 stat.

So did the customer but that information didn't filter down from the kitchen company to the tiler nor me so the mats were laid out (by the tiler) as kitchen then diner/1x2m strip in the hall then the final mat in the hall. Walls are all plastered and painted so getting second stat in would be impossible at this stage and i guarantee the kitchen company 'won't have allowed for that'.

 

[malcolmsanford]

Termination should not be a problem you can fit a nice adaptable box terminate the 2.5mm cables into that and then on into the stat. If this were me I would connect the system up without the stat and clamp meter to see what it draws

 

[Dunc]

Termination should not be a problem you can fit a nice adaptable box terminate the 2.5mm cables into that and then on into the stat. If this were me I would connect the system up without the stat and clamp meter to see what it draws

I will still end up with 4x 2.5mm solid conductors at the stat though. L+N in and L+N out due to the loading of 16A (min). The only other thing i can think to do is replace the 0.75 control cables i've already flushed in to the stat position with 2.5mm flex but i'm worried i won't be able to pull them through the capping at this stage and chopping out is not an option either.