Underfloor heating

[grommett]

My builder installed underfloor heating several months ago but did not connect to electric supply. It looks pretty simple so I decided to do it myself.

Prior to connecting, I tested the heating mat which gave me a reading of approx. 30 ohms. (approx. 20 square meters).

I have a fused spur connected to the consumer unit which is protected by a RCD. The fused spur connects to the timer/thermostat as per wiring diagram plus a connection to the underfloor temperature probe and heat mat.

The heating mat supply cable has 2 cores plus a braded outer sheath which I have used as earth. There is no connectivity between this earth and either of the two cores.

I have checked and rechecked all the connections and everything is good.

The timer/thermostat comes on when I turn the spur on and I can set the time etc. But when the heater is turned on, the RCD turns off.

Am I doing something wrong, or is there a problem with the supply? I tested the supply with the power turned off, and there are several MCB's including the one I have used that have a reading between live and earth, is this normal?

Many thanks

Yours Grommett.

 

[Taylortwocities]

The fused spur, does it have it own connection to the consumer unit, or is a spur off another circuit (eg upstairs sockets).??

If it is its own circuit then the neutral may be not connected properly in the consumer unit.

What happens if you connect something else (like a light) to the FCU instead of the heating. Does it work, or does the RCD trip?

 

[grommett]

Thanks TTC

I put a pendant/light bulb in place of the heat mat and when I turned the heating control on the RCD turned off. I removed the pendant so there is no load and this time the power stayed on. The fused spur is connected directly to a 32amp MCB via about a meter of cable. (Both the heater control and consumer unit are in the utility room). I am using the same MCB as the rest of the utility room which at the moment only the central heating boiler is turned on. Taking on board your comment about neutral, I have noticed that there are two neutral buses in the consumer unit so I will try moving the neutral to the other bus.

Yours grommett

 

[grommett]

Just FYI, I changed the neutral and all is good. Many thanks for the clue!

Grommett

 

[Taylortwocities]

Cool, glad it wasn't anything serious (like a screw through your floor!)

BUT

Whoever connected the circuit to the consumer unit should have tested, certified and notified the new circuit and that would have shown up.

Hey ho. Have a good New Year.

PS. Try the

Untitled

• Taylortwocities
• 9 Sep 2009
• 34

button. Its fun.