Heat mat fault, neutral earth reading...

[SSE]

A neighbours underfloor bathroom heating mat stopped working a while back, she asked me to look at it today. Turns out when it was installed the joiner had accidentally burst the cable for it. It's a small thin blue cable that heats up that has two conductors & an earth. Someone has done a repair on it underneath floor which looks like they have used proper kit, crimps, heat shrink etc. I've just took a voltage reading at the programmer which is fine going in & out & Ive peeled off the heat shrink & took a reading between each of the conductors & earth & on one I'm getting 150v & the other I'm getting 90v. Any ideas? Mat just needing replaced I'm guessing.

 

[SSE]

Ok. Update, she doesn't seem to think it's working correctly as there's one area where a tile is cold, then one where a tile is a lot warmer than the rest. I redid all the tests today, resistance between the two conductors is as it should be, around the 58 ohms mark, I done an IR again live to earth >299, neutral >299. Reading at the programmer is still the same, 230v leaving programmer but still voltage between both conductors & earth at the join. A friend who is also an electrician looked at it today & he thinks it's ok, possibly something to do with the type of mat or the actual cable/wires that heat up but I'm not so sure. It's like the voltage (240ish) is split exactly over the two conductors, judging by readings at join. I also bypassed the programmer & results are still the same.

 

[Deleted member 9648]

Ever heard of volt drop across a resistor?

 

[dmxtothemax]

Do you know how the mat is laid out ?
And how its's wired.
Is it just one continues run ?
Or are there several area's all coming together somewhere ?

 

[marc8]

well if your readings are correct & the programmer is working, check the Resistance of the sensor with multi meter just to make sure.
next thing get the mat up hot for couple of hours & use IR camera then should be able to trace the heat pattern around the floor, this should show if any of the heat mat has been laid under the cold spot or not, same with the hot spot might have been the spare if any & have a more dense area of the heat mat in that area.
IR camera will tell you also you can check the joint same time.

 

[SSE]

Ever heard of volt drop across a resistor?

You think this is why I'm getting those readings?

Do you know how the mat is laid out ?
And how its's wired.
Is it just one continues run ?
Or are there several area's all coming together somewhere ?

Spoke to joiner today, says it's one big continuous run, one mat. It's only an area of 6m squared. He says hotter & colder tiles are common due to density of tile adhesive.

well if your readings are correct & the programmer is working, check the Resistance of the sensor with multi meter just to make sure.
next thing get the mat up hot for couple of hours & use IR camera then should be able to trace the heat pattern around the floor, this should show if any of the heat mat has been laid under the cold spot or not, same with the hot spot might have been the spare if any & have a more dense area of the heat mat in that area.
IR camera will tell you also you can check the joint same time.

Can I ask why I've to test the sensor? Afraid I've not got an IR camera. Thanks for the suggestion though, would have been ideal.

 

[marc8]

sensor will feed back to the unit to turn floor on & off, if sensor is faulty could cause mat to turn on or off at random, normally test it during set up.
IR camera think you can hire them only need the hand held unit

 

[telectrix]

you can buy those little laser temp. sensors for < £30 on of them will do the job.