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Wired Thermostat mm² cable size

Discussion in 'Electrics UK' started by frank999, 12 Sep 2020.

  1. frank999

    frank999

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    Seems convention is to fit min 1.0mm² 5 core for a wired room thermostat, will 0.75mm² suffice, as thats all that seems available from my local Toolstation and screwfix.
     
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  3. EFLImpudence

    EFLImpudence

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  4. RF Lighting

    RF Lighting

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    Do you really need 5 core? 3 core and earth is normal for traditional mechanical thermostats, and twin and earth for digital versions.
     
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  5. ericmark

    ericmark

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    I would say likely two x three core is better, two reasons, one you should keep the extra low voltage control away from 230 volt AC, and second many boilers have a separate junction box for the ebus connection to the 230 volt connection.

    However taking Nest Gen 3 as an example even with a combi boiler there are 5 wires, L, N, E, OP1 and OP2. Even when used digital (on/off) either 4 or 5 wires depending if control is low voltage or extra low voltage, very few boilers are simply turned on/off today.
     
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  7. frank999

    frank999

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    one you should keep the extra low voltage control away from 230 volt AC
    Is that because the ELV control is carrying a 'signal', and the 230 a 'current' ... the current interfering with the signal ... note: this is a wet system, not electric heat matt.

    So 2x 0.75mm² 3 core would be advised, I understand it does not need to be heat resistant, but if it were - does that require a rubber flex, or PVC heat resistant type cable.
     
  8. RF Lighting

    RF Lighting

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    What thermostat specifically are you going to install?
     
  9. frank999

    frank999

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    A wired Underfloor heating thermostat, not sure of make yet, maybe one of the Heatmiser's designed for UFH stats, but unsure - so want to have wires available if they are ever needed.
     
  10. flameport

    flameport

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    Fit the 5 core. Covers all options. Fewer cores will save next to nothing.
     
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