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Discuss Rising Damp causing problems in the Electric Underfloor Heating Wiring area at ElectriciansForums.net

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A friend is asking for help to sort out a dispute between her Builder and Electrician each blaming the other for electric under floor heating tripping the MCB.

The electrician claims the problem is caused by rising damp. The builder says it is a faulty electrical installation.

Separately there is a discrimination problem as the heating failure takes out both the ring MCB and the main trip.

So here are the questions.

1) How much damp should the heating mat be able to cope with?
2) What tests can we ask the electrician to carry out to try and identify the cause.
3) Could my friend just install a heavy duty DPC between the concrete and the heating mat?

Thanks in advance.

Ian



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telectrix

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damp should not have any noticable effect on a properly installed ufh mat. it's possible that it was installed correctly and has since been damaged by floor layers. your electrician needs to test the mat and compare the readings with those he should have taken, 1. before installing, 2, after installing but before covering over. 3, after the floor has been laid. all 3 should be the same. if now the readings are different, then it's been damaged or affected by moisture (builder's fault).
 

James

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What is on top of the heating mat?
Can it be lifted to inspect?
If it is taking a mcb out, not just an rcd or rcbo, there should be a big black scorch mark somewhere that will show the point of failure.
 

Vortigern

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Does it pop straight away or at some point later when the mat is turned on. This is where an infra red camera can sometimes assist in diagnosis. So the spark could megger the underfloor cables for one thing. And as @telectrix says do the resistance tests to see if anything has changed. In any event your first call is the electrician as the builder wont have a clue on how to test (assuming a lot there) so spark it will have to be on first call. The point is it needs fixing, not an argument on whodunnit.
 

PEG

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Hi,this is an issue,which sounds like there is more than one,singular fault.

I am including individuals,as well as components.

The best chance of a definitive opinion,would be to employ a competent person,who can give their independent assessment,of all the factors involved,in the job.

It is not uncommon for fresh problems,causes and individuals,to pop up......say,the alarm dude,who was fitting security cameras,and managed to damage the matting with his 3 foot masonry bit,from underneath,via the kitchen ceiling....
 

Wilko

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It is unfortunately not rare (enough) that a good UFH mat is ruined by the floor layers. But of course it could be other things and I think the fault(s) are unlikely to be fixed by adding DPC.

Agree with @PEG an independent report for Owner is needed if the construction folks aren’t sorting it out. Someone here may be able assist if required.
 

Pretty Mouth

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This fault is taking out both the 32A MCB, AND the RCD? It has to be a line to earth short, and I assume it can't be located very far into the element at all, otherwise the high Zs at the fault would mean the RCD would trip first.

This could be confirmed by testing continuity of the element L-E and N-E, the L-E result I would expect to be much lower than N-E.

Seems unlikely that it's rising damp, there should be insulation below the mat which I assume would keep that at bay.
 

PEG

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or leave it disconnected and save on the leccy bill for something that just keeps your feet warm... buy some woollen socks instead.
I don't mind a bit of fun and danger,but wouldn't risk a wooly sock/shiny tile combination....and i ride a unicycle ........
 

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