Flooring Tripping RCD

[Jamie Harper]

I have fitted underfloor heating, using a WarmUp Wifi thermostat.
When i turn it on, the RCD trips after 5 seconds on initial turn on.

I have measured the following;
Live - Neutral - 39 Ohm (expected for size of mats)
Neutral - GND - >1M
Live - GND - ~150k

Now the L-G resistance of 150k seems unusual. I would expect either infinite or a direct short?

I did notice that the plasterer had slightly nipped one of the wires, but it seemed as the sleeving had just come off?

Any ideas? 150K is not ideal, but could it just be that the RCD isn't sufficient for the power required to power the mat?
Any help would be appreciated, would be devastated if it doesn't work, a lot of money and hard work down the drain!

 

[Strima]

Have you carried out an insulation resistance test? If the plasterer has nicked one of the cables then it will need replacing.

 

[electric al]

As strima said

 

[ruston]

As above, if your testing during installation was Ok , looks like the plasterer is the culprit

 

[bill01803]

The results don't make sense, if the L-N is 39 ohms the L-E and N-E should be in the same region (within 39 ohms), what have you measured it with?

 

[Sparky5473]

sounds Like the heating mat has been damaged during installation, ideally you would be looking at insulation resistance measurements of >200M ohms between line conductors and earth

 

[Risteard]

between line conductors and earth

Between live conductors and Earth presumably?

 

[Sparky5473]

Yep, also what type of flooring has been laid on top of this? Was he heating mat tested once unpacked and also once laid before any flooring work carried out?

 

[Midwest]

I'm thinking not God damn heat mats.

 

[Sparky5473]

When I fit these I test straight out of box, once laid just before next stage of flooring carried, connect my monitoring device while other flooring works carried out then test again before my connection and commissioning stage

 

[ruston]

When I fit these I test straight out of box, once laid just before next stage of flooring carried, connect my monitoring device while other flooring works carried out then test again before my connection and commissioning stage

That is the way it should be done . Test at every stage and save that sickening non event.
He did not reply if the installation results were OK.
Hopefully the nick in the cable and damp plaster may be the problem.

 

[Midwest]

Not normally plaster on the floor, well not withstanding those plasterers do slop it about

Wonder if the floor tiles ben laid? @Jamie Harper there are some companies who suggest they can locate such faults, if your floor tiles are expensive ones.

 

[ruston]

I was thinking damp plaster in the chase for the receiver lol.
I just guessed that is where the cable is nicked.

 

[telectrix]

I was thinking damp plaster in the chase for the receiver lol.
I just guessed that is where the cable is nicked.

if it is it's only a tail and could easily be repaired.

 

[Sparky5473]

Hopefully it’s nicked in the cold tail between floor and wall so should be a reasonably easy fix

 

[ruston]

@telectrix . It's the best place for it to be lol. I'm an optimist. (Sometimes )

 

[Jamie Harper]

Hi all, sorry for the late reply, i wanted to ignore it over Christmas! But i am back to figure out this issue!
So in response, i did check out of the box and everything was okay.
It appears to be where one of the wires (heating) have been nicked ever so slightly.
Now i can not access the floor, as it has 2 layers of self level, underlay and laminate on top, so no way of fixing the issue directly.

I have, however, had an idea, which I would like an opinion on.
This may be controversial...

Now the issue is only between Live and Earth, as we have established.
So do i actually need to connect the Earth from the mat to the thermostat?
I understand that earth is required for safety/fault conditions, but the whole mat is under self level, with no way of getting to it (unless drilling through the floor).
I know there will be some unhappy people for even considering this, but I can not see any reason to why not connecting the earth to the mat would cause any issues UNLESS i was to drill through into a wire for instance.
[automerge]1578318555[/automerge]

Hopefully it’s nicked in the cold tail between floor and wall so should be a reasonably easy fix

unfortunately not, it was the heating wire that was nicked....

 

[DPG]

You say 'the issue is only between live and earth'. This is the most crucial one unfortunately.

 

[Jamie Harper]

You say 'the issue is only between live and earth'. This is the most crucial one unfortunately.

But i do not connect the earth to the system, the fault does not exsist? what harm can this cause? It is a closed system effectively, the wires are in the floor with no chance of touching them?

 

[DPG]

I know what you meant, but it is not wise to remove the earth on a known faulty circuit. Especially in a bathroom.

Out of interest, why did you bother testing if you were going to ignore the dangerous results anyway?