Tag Archives: 220v

missing 1 wire from my gas heater to my Aube RC840 to finish off Nest Thermostat wiring!!!

11 Jan

Dear all,

have verified in full my previously recommended wiring  earlier this week – having a 3-wire (220 240 Volts) cable running from my gas heater, to my RC840, and 3-wire from my RC840 to my nest thermostat.

While doing this, I have actually used this to let me Nest get fully charged, updated to the latest software, and exercised it a bit.

A few comments for those who go thru this process:

  1. it took a few hours to get my nest battery charged up to at least 3.7V
  2. note that in between it may (at least mine did) reboot a few times – realizing it does not have enough energy to run wifi (required to get the update done – have no idea about the size of the download by the way, do you?)
  3. 3.7V is critical as it is the minimum Nest needs to be able to launch software updates
  4. once update was done, an easy trouble-free process, I was able to fully control my nest via my Ipad

I live in an 1930s building, and our apartment got renovated to the current Electricity standard a few years ago (meaning I have a decent amount of extra wires running thru the various electricity access). Frustration rose when I realize I did NOT have a 220 240 Volts with 6-wires but 5-wires!

This means I can’t properly wire the Ns/Ls/Lr from my heating unit to the RC840T (I had planned to locate it near my fuse box – opposite from my heating unit).

So I have paused my installation – and – it looks like the only alternative is to change the heater supply cable and upgrade it to a 6-wires one.That’s assuming of course, I have room to retrofit it!! If you can think of anything else to do… please chime in now!!

In any case, I have updated and confirmed now that the diagram below is fully working.

nest thermostat 220v rc840

if you can’t figure out how is laid out the apartment and how the wiring has to run, I will draw up a schematic of the flat and the way the wire will be running thru.

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Electrical wiring of my previous 220 240 Volts (high voltage) thermostat to my gas heater

21 Dec

default wiring for high voltage thermostat

220v thermostat wiring dry switch

to all, above is a drawing of my previous configuration using a “2-wire” thermostat, high voltage that is 220 240 Volts, directly connected to my gas heater.

couple of key points:

#1 the thermostat had batteries internally used to trigger the “dry switch” (now on the drawing).

#2 upon “heat” command (ambiant temperature below target) the “dry  switch” basically closes the electrical path between Ls and Lr

#3 once Ls and Lr are connected together, this triggers the heater (gas + circulator)

#4 Ns connector is shown although not used in this configuration since thermostat operates from its own supply (internal batteries)

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.

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