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I have a 2850W electric UFH system in a large conservatory (19m2 x 150W mats). The conservatory has its own consumer unit for all electrics. The heating is fed from a 16A breaker to a 13A fused spur and controlled by an electronic timed thermostat (rated to 16A).
This setup was wired in by an electrician 3 years ago and has been 'fine' until yesterday when the fused spur got a bit hot and smelly. On inspection the fuse holder has discoloured but no signs of loose or damaged wiring.
Today, i've fitted a new fused spur and it still gets warm. I suspect the draw of the heating is flying a bit too close to 13amps and the original spur finally gave up. Having realised this, what do I do now? I'm under the magic 3KW limit for a 13amp circuit but obviously too close to it. Do I get an electrician in and upgrade the circuit or treat fused spurs as consumables? I don't really want to die in a house fire.
Blah, blah, blah, blah I don’t really want to die in a house fire.
Get an electrician in 😉
I don’t really want to die in a house fire.
Look on the bright side, at least you'd be warm 😁
Is the whole circuit 16A except the bit between the fused spur and the thermostat? Or all the way from the breaker? How easy is it to replace those wires and use a 16A fuse instead of 13?
Might be a simple DIY job. Might also invalidate your home insurance (if they know about it, ahem).
johndoh possibly has the best answer here...
Assuming it's wired in 2.5mm T&E from the CU, you can replace the fused spur with a 20A DP switch. Go MK as they're usually the best make. It doesn't need to be fused, just a point of isolation.
Also if you used the same 13A plugtop fuse that might be your culprit as the metal end caps may be tarnished. The 20DP doesn't need a fuse so that eliminates that possible issue, also cheap (not saying yours was cheap!) fused spurs don't grip the fuse well and might be ok with low currents but as you're pushing 13A it's struggling.
Fuses running close to their limit will run warm though, the fuse element is cased in silica sand but will be warm to the touch if it's loaded at max current (higher current = heat).
IAAE
Could be a couple of things.
I'd get someone in to check all of the circuit from consumer unit to mat - could be a slightly loose connection at the consumer unit end or damaged mat, has there been any obvious damage anywhere over the area of the UFH?
Damaged mat would increase resistance & current drawn.
The mat is just a resistive load - you could disconnect from the controller etc and check the resistance of the mat, quick maths suggest it should be around 18 ohms.
Have any other appliances had an issue, are your lights dim or flickering? - check things like kettle plug top etc in case there is an issue with your voltage - if this gets low it will increase current draw too, should be between 216.2 volts - 253.0 volts (UK tolerance of -6% +10%).
But don't just keep swapping fuses & accessories as there could be more of a problem.
Thanks for the replies. No evidence of damage to the UFH nor reason to suspect it. No other electrical gremlins in the house. Yes 2.5mm T&E. Didn't reuse the fuse but the new FCU was whatever brand my local DIY store sells, not MK...
Fitting a 20A DP is where i'm leaning after more reading around. Warm/melty FCU certainly seem pretty common! For peace of mind I have called an electrician, but it's in the lap of the gods if he responds (IME electricians are the toughest trade to actually hire!).
I'm hopeful that a fiery death is not imminent.
I’m hopeful that a fiery death is not imminent.
My motto.
With that thread title I thought we might be discussing one form of capital punishment
It’s not the Spanish Inquisition
2nd Dirk, don't discount a damaged element. I attended a fire caused by a UFH mat in a conservatory. Clear signs of overheating in the FCU. People were lucky and noticed it quickly but damaged a large section of their floor.
Fused spurs don’t like being run close to 3K for any time, you get this happening where immersion heaters are connected to them. I’d first check the UF heating for damage, test the resistance against manufacturers spec, and if ok switch the switched fuse to 20amp dp
Test the element / mat.if you have a clamp meter and can get it round one of the wires (will require fused spur off wall ) you can get an idea of current drawn. View over time. Sometimes these things get worse as they heat up