Electric Underfloor Heating - Tripping RCD

[Daniel Coakley]

Hi all, wondering if anyone can help me with a recent issue I've had with electric UFH in a small flat. Found that when the UFH starts, the RCD trips immediately - this started last Saturday while I was away. Prior to this, I had heard some buzzing coming from near the UFH unit controller in my kitchen, but didn't realise there was an issue.

Here are some details of the system

• Controller: TH-132 (15A RES Max.)
• Mat area (total) ~ 5m2 (covers a small kitchen and hallway)
• Installation Date ~2005 (it was installed before I moved in, so I don't have any manufacturers details / specs)

I did some checking yesterday and noticed that the UFH controller is fed from a wall socket in the kitchen. When I opened the socket, I noticed the earth had come free of the terminal, and there was some evidence of arcing damage on the live wire at the terminal also. I pared back the line and earth, and refitted them, thinking this might solve the problem (and might have explained the buzzing I'd heard). When I reconnected the UFH, the problem was still there, and the RCD tripped immediately.

So, pulled out the multi-meter and ran a few tests. Results as follows:

• Tested resistance across mat (LOAD L/N) = ~28 ohms
• L-E > 1 Mega Ohm
• N-E = 29 ohms

I am writing this post from memory of the readings I took yesterday so I may be slightly off. As I don't know the spec of the heating mat, I have to assume the resistance reading I got on the mat seems reasonable, as it would equate to ~8.5A current (which I assumed was about right given what I've seen for a system this size (here's the resistance table I was comparing from another manufacturer).

Insulation test on Line to earth seems okay, but Neutral to earth is not? Am I correct in thinking I should be getting the same reading across both of this. When I carried out the test, the RCD was off, but Main switch was on.

Does anyone have any idea what the problem might be, or what further tests I should carry out to diagnose the issue? Was hoping this was a problem with the main wiring or controller, as I can't afford to take up teh floor right now, and it's not going to be a fun Christmas in Scotland with no heating .

Any help is much appreciated

 

[Silly Sausage]

View attachment 46545

Rough as ...!

 

[Markyd]

grey cable to live?........is that yellow cable definitely an earth?
sorry C.P.C

 

[Strima]

Looking at the state of those conductors I would completely disconnect and get someone round to test it fully.

 

[DPG]

Agree with above. It needs a spark in to a) test it, b) tidy it up, and c) ensure it has proper fuse protection.

 

[telectrix]

as hhd said, dis. the mat leads completely from the contoller and IR test them. L-E and N-E.... L-N should read on continuity, anything from 20 ohms upwards depending on the wattage rating. if those readings are good, then look back towards the socket.