This has me mystified!

[buzzlightyear]

is it tiled Murdoch ?

 

[marconi]

Studying the construction of the Magnum heat foil there are Line and Neutral metallic edges running left and right along its length. The heating elements are strips connected between these edges at regular intervals. There is no metallic foil above or below. The N is earth referenced so there is a voltage gradient both between the edges along an element but also to the flooring beneath. Is the polystyrene heat and sound insulating layer in place? This layer would also act to electrically insulate the elements from the flooring which is at local ground potential.

The floor underneath, if it is concrete will have conductance which depends on its chemical make up and moisture content. Wet concrete might have conductivity of 100 OhmMetre whereas very dry concrete 100 MegOhmsMetre. (see : Electrical conductivity - http://www.concrete.org.uk/fingertips-nuggets.asp?cmd=display&id=996)

My pondering is each heating mat will inevitably have a high resistive and capacitive leakage because of the close proximity and large conducting surface area of both the element and floor beneath and above. The polystyrene insulation would reduce these leakage components.

More mats - more leakage current.

I wonder too if there is a best way to lay the mats side by side to minimise leakage current ie:

Is N-L L-N N-L L-N arrangement better than N-L N-L N-L N-L? I have not formed a definite view yet on which is likely to be better but I have a hunch it is the latter.

Time I think to do some earth leakage current measurements to learn more.

Reducing both the maximum potential difference between the mat and the floor and the potential difference to earth across the mat would reduce the earth leakage current. So feeding the mats by a 240V supply galvanically isolated from the mains would reduce the leakage current.

Other than this probably impractical and uneconomic potential 'solution' I reckon it is a question of digging up and re-installing correctly with the polystyrene and metal foil layers.

All academic thinking but maybe of some use to you.

 

[buzzlightyear]

possible that he has nick it on the cable and a dead short .and has it some damp.
Click to expand...
The live and neutral cables are singles .....I might agree with you on that one

 

[PEG]

The humming is a bit of a concern...maybe a glass on an ear,could locate the spot?

 

[stevethesparks]

I dont like electric UFH at the best of times, when pressured into installing it I always use the warmup brand. The mat in the link looks pretty fragile to me, and I particularly don't like the method of crimping connections to it as shown in the image.
If you have 1M between conductors and a local cpc, then in my opinion its end of story, it needs replacing.
Out of curiosity, what sort of room is this mat installed in?

 

[Octopus]

^^ conservatory

 

[David M]

I agree with, it sounds like the mat was damaged during the installation of the floor covering (tiles) and damp has created an earth fault path. If the installer didn't follow the manufacture's instructions and laid the mat incorrectly then its likely any warranty will be void. Some mats are repairable, but looking at the design of the mats I doubt these are repairable. They look very susceptible to damage, a carless tiler could easily nick the mat with their trowel. Especially if it has been incorrectly/poorly laid. I don't see an easy solution to this, to guarantee a fix. Its looking like tiles up and start again at minimum the section where the fault is.

 

[Octopus]

Its a wooden floor and the mat is simply laid beneath it.

 

[marconi]

A long shot idea - if it's wooden flooring is there a nail through the insulation of a cable at some point along the edge against the skirting board? How to find - IR test to each nail head?

 

[buzzlightyear]

A long shot idea - if it's wooden flooring is there a nail through the insulation of a cable at some point along the edge against the skirting board? How to find - IR test to each nail head?

I doubt that, I have never seen a floor layer nail a wooden floor yet.glued and knocked in to position
if he did nail it, they call it secret nailing where you can not see the nail.

 

[Midwest]

Your giving me nightmares Murdoch

 

[Octopus]

Thanks to all that contributed.

Just spoken to the installer (who travelled from Oldham to Surrey) and he's planning to replace the mat completely...... with a more traditional unit.

 

[Midwest]

Thanks to all that contributed.

Just spoken to the installer (who travelled from Oldham to Surrey) and he's planning to replace the mat completely...... with a more traditional unit.

Hope those tiles weren't too expensive!

 

[buzzlightyear]

Just spoken to the installer (who travelled from Oldham to Surrey) and he's planning to replace the mat completely...... with a more traditional

now that's could cost him a pretty penny .

 

[buzzlightyear]

when I wire up a heating mats ,I tell the installer before you lay any thing on top first .
I will test before hand it so there is no hiccups.