This has me mystified!

[Octopus]

Ok. based on another recent thread I hope we can get to some sensible suggestions to this conundrum I have due to a visit on my way home today!

Underfloor heating (recent install) is tripping the RCD - the CU has all socket circuits and lighting circuits on the RCD so when it trips pretty much everything goes off.

Underfloor mat is this stuff:

Floor Heating | Underfloor Heating Foil - https://www.magnumheating.co.uk/products/32-1-floor+heating+/p-226-MAGNUM+foil+set

There is only the L & N running from the controller to the mat, so no CPC and thus its not possible to IR the system

An IR test from the L of the mat, (L & N both disconnected from the controller) to the CPC of the socket circuit its connected to via a FCU only gives just over 1 meg ohms.

End to end reading is OK.

I did a direct connection from the FCU to the mats and it tripped immediately .

The installers put this down about 6 weeks ago and its not worked properly since then.

The mats are laid side by side and with 5 mats connected the RCD goes immediately, with only 2 connected, the RCD holds. Which points at one of the 3 disconnected units having an issue but the installer says it has worked with all 5 connected.

What was interesting is that when the mat is on, there is a distinct "hum" from part of the floor.

Having read the manufacturers website and checked with the installer, they didn't use the damp proofing foil!


Any comments, sensible or off topic please - I've never seen this stuff before and hope some of you have!

thanks

 

[static zap]

See if any mats more lively with a volt stick !
(design sounds -iffy + situation makes worst - Till it dries ?)

 

[Octopus]

possible that he has nick it on the cable and a dead short .and has it some damp.

The live and neutral cables are singles .....

 

[telectrix]

sounds strange to me.all the ufh elements i have ever come across are a coax cable. the inner is the element L-N (end to end), and the outer is cpc.

 

[Christopher Bernard]

Did you test both the neutral and live against the cpc of the sockets? also I wouldn't go by what the installer says.

 

[Wilko]

Hi - I've not used that foil, it looks fragile for flooring installer use (sorry to be blunt). My 20p is one of "the 3" has been punctured and is in contact with the original concrete floor (?), but you'd think IR would be lower ... And the buzzing is the mat vibrating in the space between new flooring and original floor (not properly secured?).

 

[Octopus]

sounds strange to me.all the ufh elements i have ever come across are a coax cable. the inner is the element L-N (end to end), and the outer is cpc.

Likewise and thats why I posted this...... hoping somebody else had installed it!

 

[Octopus]

Did you test both the neutral and live against the cpc of the sockets? also I wouldn't go by what the installer says.

Hum - the ends of the mat were both tested to CPC at the sockets

 

[telectrix]

what's the end-end continuity of each?

 

[Octopus]

They were linked in parallel so the reading was 64 ohms - the connections are very rough IMHO and I didn't want to undo them.

 

[Darkwood]

I take it they used the polystyrene insulation plates?

Given they haven't followed manufacturers instructions and now have a earth leakage fault then I suggest damp has got into the insulation plates if fitted, my advice is be blunt and tell them it will have to come up and be done properly if you are to try repair it and put your name to it.
The humming does sound like tracking or arcing so suggest the mat is damaged or badly terminated.

 

[AJshep]

I've not seen or used this heat mat, however I've used a similar looking product years ago when I was still learning. It was supplied by a conservatory company, I can't remember the make but it came on transparent plastic laminate it only had a L & N connection that that pushed onto a terminal on the mat, it looks very similar to your product.

Had a few issues all had the same problem it was where the push-on L&N connector didnt quite make a solid connection on the mat, it got hot around the connector and damaged the mat.

Not saying this is the problem here, and it was about 17 years ago so but it was similar symptoms to what you have described.
I remember it well because I got the blame !

 

[Richard Burns]

Perhaps an IR test from the mat leads to the floor itself (perhaps with water on it) to see if there is a connection to the floor, there may be an alternative route through the ground rod back to the RCD.

 

[Octopus]

Perhaps an IR test from the mat leads to the floor itself (perhaps with water on it) to see if there is a connection to the floor, there may be an alternative route through the ground rod back to the RCD.

???

 

[Richard Burns]

???

Through the ground, like an earth rod,

error in editing!

 

[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.

 

[David M]

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

A floating laminate, or a tongue & groove solid wood? The solid wood tends to be glued and is generally more expensive and occasionally nailed, (which I doubt the floor fitter would be dumb enough to do this considering UFH is installed, or would he?).
Anyhow if the UFH installer is happy to come and sort it, that's just the job.
What will be very interesting is if you can find out exactly what the cause of the fault was and let us all know!! Cheers!

 

[HandySparks]

Just spoken to the installer (who travelled from Oldham to Surrey)...

That's pretty mad, especially when there's a risk of a callback. I shy away from jobs more than a few miles away.

 

[pe2dave]

Hi - I've not used that foil, it looks fragile for flooring installer use (sorry to be blunt). My 20p is one of "the 3" has been punctured and is in contact with the original concrete floor (?), but you'd think IR would be lower ... And the buzzing is the mat vibrating in the space between new flooring and original floor (not properly secured?).

Customer response to 'buzzing'? I know I'd just say fix it please.

 

[davesparks]

The foil type underfloor heating is a terrible idea in my opinion, I’ve seen it once before and I didn’t like it at all.

It is basically constructed like a rear window de-mister on a car, there’s a L and N bussbar formed by a copper strip running along each side of it with heating elements between them. All this is sandwiched between two thin flimsy bits of plastic.

 

[mattg4321]

Far better is something like the HeatMat Combymat, which I've used a few times under laminate/engineered wood flooring.

150W Combymat System - http://www.heatmat.co.uk/product-range/underlaminate-systems/combymat-heating-mats.html