UFH mat blowing fuse.

[lizzardtong]

It's blowing the fuse on the main board.
The only thing that is nagging me is that the main consumer board is blowing. Is this normal? I would have thought that only the spur fuse would blow.

is it blowing MCB OR RCB in consumer unit?

 

[Diggy]

If its on the main board then surely it must be in the wiring after the FSS , and therefore probably nout to do with you.
If it's in the UFH then the fuse in the FSS would blow wouldn't it?

My 50p is on a nicked neutral somewhere down the line between the other side of the FSS and the main board. :0)


Thats my guess anyway as a non sparky anyhow. :0)

Keep us informed.

Good luck

Diggy

 

[Sean Kelly]

Arggh……………………it was my fault!

I met up with Steve Ashby just before Xmas. What a nice chap he is. His equipment is basically a Ghost Busters kit with dials and probes, wires and bleeping devices etc. It did not take him too long to find the fault. I always take photos of UFH cables prior to SLC. This helped speed up the diagnostics.

He had to remove a tile and some skirting by the back door. He removed the termination crimped end of the cable and re-crimped it with a thinner crimp. This slimmer crimp did not protrude as much as the last one. He then used a cable pin and pinned it to the plywood floor.

The first picture (which was taken at installation) shows the end of the mat terminating by the back door. Well, it’s actually terminating in a void under the skirting. So basically, the last 2 inches of the cable is neatly tucked out of sight. Why did I do it?................I did it because the last bit of the cable is nearly always double the thickness of the wire because it has been crimped. I did not want it sticking above the SLC when it was poured.

The SLC was poured and I tiled. That was last April. The heating has been on throughout the Summer, but when it turned cold and wet that is when things went wrong.

Where I went wrong…………………The entire cable (apart from the cold tails) should be encased in SLC and/or tile adhesive. There should be no voids. What I should have done on this occasion was to make a hole in the ply and bury the end of the cable. Then cover it with SLC.

UFH cables heat up to about 70degrees. As a comparison, a hot glue gun heats up to about 120degrees.

The heat generated by the cable needs to be drawn away quickly, this is achieved by the surrounding SLC/tile adhesive and tile. The end of my cable was open to the elements. So when it heated up to 70degrees the heat built up around the cable and the resin inside the crimped cover melted. You can see the blob of resin in the second photo. The end of the cable is now even more exposed and it is drawing in moisture from the atmosphere which eventually causes failure.

So in the end it was a day of learning off Steve. It was also a day I had to hand over some money to pay Steve for his services. However, my customer said that they would pay half the costs. I was astounded. What a kind gesture………………..an offer I eventually accepted!

I chatted to Steve about the Tilersforums and he said he had heard about the forum from another tiler (I think it was Bugs183), when he cut through a cable in a doorway!

So remember to make sure the hot part of your cable is encased in concrete. Do not leave any exposed cable under cabinets or skirting (it was literally an inch of exposed wire that cost me over a days wage).

 

[Sean Page]

I attended a UFH training course run by Raychem a few years back and they showed us the thing with the Megger Tester thing.

With our normal installation tests (I do the same as you Sean) small faults in the insulation wouldn't/didn't show up but when they pumped 1000v through it you could actually hear it sparking.

I usually have one of the Warmup alarms connected when I'm tiling, but they wouldn't detect hairline fractures. When I asked they guy if there was any point to the alarms he said that as fitters we can only do so much, unless we wanted to invest a lot of money (and training) in a megger tester that would probably never really be needed.

I would push this back towards the manufacturer and hope the customer sent any guarantees off