Underfloor Electric Heating Issue

Discussion in 'Electricians' Talk' started by 29guitarman, Jan 6, 2020.

  1. 29guitarman

    29guitarman New Member

    Hi All,

    I have recently installed electric underfloor heating, and unfortately it isnt working...

    So, the floor was installed well, i checked the continuity and insulation between wires as i was going along, all as expected.
    Now due to the floor not being level, i applied the first layer of self level, yet it still left some wires showing, not an issue but something i was very cautious about, yet one of our tradesman was not so cautious and slightly nicked one of the wires. I checked the resistance of the L&N and it was as expected and carried on laying the rest of the self level.
    Now.. to today. Flooring is down, mat is burried below 2 layers of self level, underlay and laminate. Wiring has been finished and thermostat connected.... turn it on and it trips the RCD.
    Go to measure between the matt wiring:
    L & N - >200M - good
    N & E - >200M - good
    L & E - ~150k - Not good

    Obviously the nicked wire caused a slight resistance between Live and Earth... damn.

    So i have a controversial solution and would like peoples opinion.

    Now, as the heat mat is burried, do i HAVE to connect the Earth from the mat?
    This would remove any issue I have.
    Now i understand that the earth connection is there to provide safety against a fault, yet there is no way of getting to the wires unless you were to drill down into the wires (which no one should do if the electric is turned on, earth or no earth).

    I know this is probably going to cause some controversy, but would like to know people opinions.

    Happy new year!
    Thanks
     
  2. MGW

    MGW Screwfix Select

    Had the same problem, had to rip it all up and re-lay new. Since you know where the problem is, maybe you can expose that bit and repair, but much depends on type of heating cable, some has one circuit, some has multi circuits you can often see a thinner bit, there is also the rayochem.

    I would never ever consider removing the earth. If the line is connecting to earth, then clearly it would be making part of the floor live, if the floor was insulating then it would not be tripping the RCD, so removing earth is a non starter.
     
  3. 29guitarman

    29guitarman New Member

    Thanks for this, to do this it would require taking layers of self level off, and possibly damaging the cable even further. So not really an option.

    As the floor is under multiple layers of self level and laminate on top, the mat is effectively insulated from the 'outside world', no?
    Its not something i am wanting to do, but at the same time i cant see a direct danger?
     
  4. Comlec

    Comlec Screwfix Select

    No one in here is going to suggest you remove the earth. The heating mat is now faulty and should not be connected until repaired or replaced.
     
    MGW likes this.
  5. Bazza

    Bazza Screwfix Select

    The floor screed will be 'earthy'. At some point, there will be external things (like metal water pipes) that touch the floor screed. So it is not insulated from the outside world.
    The RCD doesn't need much 'earthyness' to make it trip.
    It is just possible, in a month or two, when everything has dried out that it won't trip. But its unlikely.
    Don't ever disconnect the earth, you have a possible live wire in the floor.
     

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