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.
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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?

 

[Jamie Harper]

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?

Its not in a bathroom, its in a kitchen.

It's not that i was always going to ignore dangerous results? My main issue was always ensuring the resistance between L and N were maintained. I never expected this to occur, if i had measured the L & E when i noticed the nick in the cable i would have corrected it, but unfortunately i didnt test it...

Its not a dangerous result either? it if were a direct short i would be more concerned, but this obviously shows a very minor error, hence why i cant see an issue with just not connecting the Earth?
I am well aware it is not 'advised' to do this but before i do anything i would like to know people thoughts on what issues it could cause and why it shouldnt be done?

 

[telectrix]

it is dangerous. diss the earth wire and you could end up with a floor that's "live". look what happened to those 3 horses at epsom or wherever. might be a stimulant for break dancing, but not advised.

 

[DPG]

Apologies, not sure why I assumed bathroom. But the principal is the same.

It's a shame it wasn't measured after the first covering layer went down, but no going back now. Who layed the levelling compound? I would be getting them back rather than leaving a potentially dangerous situation.

 

[Jamie Harper]

Apologies, not sure why I assumed bathroom. But the principal is the same.

It's a shame it wasn't measured after the first covering layer went down, but no going back now. Who layed the levelling compound? I would be getting them back rather than leaving a potentially dangerous situation.

It really is a shame, and unfortunately is was me who did it all. Only myself to blame.

Just out of curiosity, what voltage is supplied to the mat, is it just straight 230V or is it usually stepped down?

Like I say, it is not advised at all and i fully understand that. It's just that i see a very small leakage to ground via the Live, and there is no way anything could be touching the wires, no central heating or cabinates, its all effectively insulated by the self level and laminate flooring. It does make me nervous considering this, but i would like some solid proof that it would cause an issue, as currently i cant see any direct danger?

 

[DPG]

These things happen. We all make mistakes.

What you need to bear in mind now though is that you and your family will probably be walking barefoot on this floor. And you do realise how small a current has to be to cause injury?

 

[Jamie Harper]

Another idea one of my engineering colleges had was to try and' burn off' the fault. Obviously the fault is very minor and not a direct short. If I was to use a form of power supply and connect the Live and Earth of the mat up, it could potentially burn the fault away, but i am a little skeptical of doing this. I have seen this method used in various scenarios, but dont want to completely destroy the floor if there are other methods.
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These things happen. We all make mistakes.

What you need to bear in mind now though is that you and your family will probably be walking barefoot on this floor. And you do realise how small a current has to be to cause injury?

Thats the thing, it doesnt take much at all, especially with high voltages used.
I guess it depends on how insulating the self level and flooring would be?

 

[Midwest]

I came across a L-E fault once, where a lighting circuit cable had been nicked by a nail. Had been left like it for years. The whole wall was at supply voltage. Didn't come to notice, until the client decided to have their bathroom refurbished, and the plumber got a shock off touching the wall and water pipes. Never would of believed a plastered wall could conduct electricity, but saw it for myself, so I wouldn't leave it as is @Jamie Harper.

As posted before here I think, there are companies out there, that boast they can trace the exact location of the damage, and repair it. Think its expensive, but might be a solution for you.

 

[James]

It is unfortunate that there is some damage to the heating cable.

it is absolutely not advisable to just remove the earth connection.

• anyone who was to work on the circuit in question could be in danger due to a LIVE (earth connection)
• the earth cable in the heating tape will be surrounded by ground (levelling compound, concrete etc) it will act like a grid and try to bring that section of floor up to 230v. it will be reduced voltage due to contact with the surrounding ground.
• there will be a constant current flow from live to earth that will increase your electricity bill.
• voltage of your floor will vary depending on many factors outside your control. ground water level, humidity, cracking or other damage to floor or substrate, salinity, spillages etc.
• if the circuit is supplied via an rcd or rcbo, it will cause nuisance tripping anyway as there will be times when there is enough current flow to real earth to trip the device. If it is not rcd protected, then see below.
• 
  
• it is quite feasible that one evening, maybe many years from now when the conditions are just right, your wife, child or grandchild will get up in the night, walk in with bare feet and turn the tap on for a glass of water. By holding the well bonded tap and standing on the faulty floor they make the circuit complete and you have to come down to find them dead on the floor in the morning.

Thankfully,
I am one of the majority of electricians that has never had to explain myself to a coroners court or a family of the deceased. I don't know what would be worse but I hope, ensure by good morels and working practices that I am never in that position.

You say your idea is a bit controversial, I am amazed that you have not been hammered for even suggesting it.

you have your profile hidden so I don't know your electrical skill set,

if you are a professional electrician SHAME ON YOU

if you are a diy guy
Please look at what I have written above, whatever expense and/or inconvenience is incurred, is not important. we all screw up every now and then. its how we deal with it that makes us who we are.

Bottom Line, your options are.

1.. rip the floor up and do it again, this time get it right.
2...cut the cables off where they enter the ground, put a radiator on the wall.
3....SAVE MONEY AT THE EXPENSE OF PEOPLES SAFETY.

 

[electric al]

I know its disappointing to think you've messed up by not testing it before the floor went down .
I can also see that you don't want to take the floor up now it's done.
The question is , can you live without underfloor heating ?
Someone may not live if you have a live earth fault and do what your suggesting .

 

[Midwest]

I was thinking the OP is the home owner, might be wrong.

 

[Strima]

To even suggest disconnecting the earth means you should not be doing any sort of electrical work. It is often said on the forum to 'get an electrician in', this is a prime example of why it is said.

Two options:

1. Disconnect the mat and chop off the conductors so they can never be connected.
2. Rip the whole lot up and start again.

The vast majority of manufacturers will insist on testing at various points of installation to avoid this scenario.

 

[James]

I was thinking the OP is the home owner, might be wrong.

I agree, I think they are the home owner.

I understand the risks of electricity and am almost shaking at the thought of one of my grandchildren being electrocuted in my own home, therefore I ensure it is SAFE.

I could not deal with anyone being killed or injured by my own incompetence. let alone one of my loved ones.

but just think all of you, how would you feel if you have managed to save a couple of grand by not re-doing a bad job and your granddaughter paid with her life?

replace the word granddaughter with anyone you feel is going to cause you to breakdown if you killed them.

I will not respond to this thread again, I will end up getting emotional and saying something I shouldn't.

 

[electric al]

I was thinking the OP is the home owner, might be wrong.

Well yeah I was assuming that too . Surely knowing the danger of such an action you wouldn't willingly leave someone else to pick the slack up

 

[westward10]

@Jamie Harper you have options here as quoted in several posts in this thread. Your suggestion of removing the protective conductor is not one of them and no member on here will condone this.
Thread closed.