Switching 40A Underfloor Heating

Discussion in 'Electricians' Talk' started by micktheknife, Apr 12, 2015.

  1. micktheknife

    micktheknife Member

    Good morning,
    Would anyone be able to advise another way to switch a 40A underfloor heating mat other than a contactor? The client is question is complaining about the 'clunk' every time it switches on and off. I have tried to different contactors but both makes make about the some noise. The contactor is mounted in a local consumer unit adjacent to the room with the heating.


    Any help would be much appreciated.
     
  2. unphased

    unphased Screwfix Select

    I question the 40A! What's the floor area heated? 40A is mighty big for an u/f electric system.
     
  3. micktheknife

    micktheknife Member

    Hi Unphased it's a 41m2 conservatory fitted with 200w per m2 mat so comes in about 35A :eek:
     
  4. unphased

    unphased Screwfix Select

    How is the temperature of the mats controlled? The mats I have installed are usually limited to a 16A rated controller/timer. How is this done with 40A? :)
     
  5. micktheknife

    micktheknife Member

    The 16A Controller/Timer feeds the coil of the contactor.
     
  6. unphased

    unphased Screwfix Select

    but you then have 35A going through a 16A rated device after its switched.
     
  7. micktheknife

    micktheknife Member

    A 6A control circuit from consumer unit feeds the Thermostat/timer. The load side of the controller feeds the coil of the contactor which energises the 35A load of the underfloor heating ;).
     
  8. unphased

    unphased Screwfix Select

    I think there is possibly some mis-calculation here? The 200W per m2 doesn't sound right to me. I would say that you possibly have 200W per mat. How many mats do you have in total?
     
  9. micktheknife

    micktheknife Member

    The 200w per m2 is recommended for conservatories by the manufacturer.
     
  10. micktheknife

    micktheknife Member

    Unphased - Are you sure you have fitted underfloor heating before??
     
    Lectrician likes this.
  11. Lectrician

    Lectrician Screwfix Select

    Look for a 40amp triac / solid state switch.
     
  12. micktheknife

    micktheknife Member

  13. Lectrician

    Lectrician Screwfix Select

    Most have derating factors if you don't use a heat sink, look at the spec, you may need a much larger one than 40amp if you don't want a heat sink.
     
  14. Lectrician

    Lectrician Screwfix Select

  15. unphased

    unphased Screwfix Select

    Perhaps getting confused. The most recent one I installed was coiled wire. Both coils totalled 1.8kW each so I had 3.6kW total and that was for a similar floor area. (16A) I don't understand how you have a 35A load that's all. :)
     
  16. micktheknife

    micktheknife Member

    The one you have linked to seems ideal for the job - Thank you, One last question - does it matter what size the heat sink is? they seem to come in many shapes and sizes??
     
  17. Lectrician

    Lectrician Screwfix Select

  18. Lectrician

    Lectrician Screwfix Select

    Usually optional extras made for it.
     
  19. micktheknife

    micktheknife Member

    Unphased - 200w/per m2 x 41m = 8200w.
    8200w/230 = 35.65A
     
  20. micktheknife

    micktheknife Member

    Superb Lectrician - Thanks very Much For Your Help :)
     

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