electrical schematic of nest thermostat with 220 240 volts heating system

19 Dec

nest thermostat 220v europe

nest thermostat wired to a 220V heating system

following request for clarification,

here is my understanding of how this works, and particularly what is the RC840-240T doing for you.

#1 RC840T-240T is overkill – this box is designed to drive directly an electric heater (2kW or so…). this means the relay in this box can carry a lot of current

#2 note this device is not approved in Europe, probably because of 50Hz and 220 240 Volts (versus 60Hz and 110 Volts), so a new certification would be required.

#3 and I Will pause here, I have a doubt about the need (or not) for the C wire to be connected honestly, so I will investigate and report back once I have a chance to spend more time.

8 Responses to “electrical schematic of nest thermostat with 220 240 volts heating system”

  1. Robert December 20, 2012 at 08:57 #

    Nice to see you taking this up seriously, maybe a legend and accompanied explanation would help.

    • usingnestineurope December 20, 2012 at 09:07 #

      Robert, thanks for your feedback – will amend drawing and explain how this all works.

      I agree what’s missing particularly also is what’s in this box between the heater and the Nest Thersmostat.

      stay tuned but keep it coming this is good,


  2. Peter December 20, 2012 at 23:01 #

    you have been posted that you only have 2 wires with 220v from your heater but in your schemma we can see 3 wires named (Ns, Ls, Lr). Could you explain that? Thanks!

    • usingnestineurope December 21, 2012 at 07:17 #


      This is a grest question you are raising!
      I will create a schematic showing my default 220v thermostat setup (with my 2 wires) and this will help clarify why we need the 3rd one when using nest thermostat connected thru this box.


  3. Aytek October 7, 2013 at 20:07 #

    Hi usingnestineurope,

    Is Aube also a thermosthat? Is it logical to connect to thermosthat together ?

    • usingnestineurope October 8, 2013 at 00:05 #

      Aube’s RC840 is NOT a thermostat. it helps converting 220V signal to 24V which is within the range of signal Nest can use.

  4. Roberto Aste August 24, 2016 at 13:20 #


    Is there a video of the instalation?


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