Finishing Touches: Installing Nest w/ Line Voltage

If you haven’t seen the information on how I set it up initially, check out the first post here: http://blog.anthonyngu.com/2016/12/12/bridging-the-gap-between-nest-and-line-voltage-thermostats/

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This is how it was left hanging for about a week before I bought an electrical box at a nearby Home Depot that would fit next to my original electrical box so I could begin mounting it. Steps for the finishing touches were as follows:

  1. Cut out a bigger hole in my drywall (making sure that it was still small enough to fit under the included mounting plate)
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  2. Mount the transformer/relay next to the original electrical box. (Something to keep in mind: Double check to see if your original electrical box is bigger than its opening. If it does, you will most likely not be able to place another box right next to it without have to do some patching of the drywall after)
  3. Paint over any small marks or discrepancies with the mounting so that it would look as good as new!

The bigger hole was still small enough for the face plate to cover (included with the Nest) and I was able to paint over the edges to make it look as good as new!

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Bridging the Gap Between Nest and Line Voltage Thermostats

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I recently decided to switch my old thermostat to a Nest and figured that it should be easy considering my current thermostat just controlled a simple electric wall heater. Unfortunately, it was only after taking my old thermostat off the wall that I realized that it was in fact a line voltage thermostat (Honeywell’s T410AA), which means that it uses high voltage (240 V) and acts as an in-line switch between the electric wall heater and the power supply. The problem with this is that systems like the Nest run off of low voltage (24 V) and can’t be used to switch a high voltage system.

To fix the issue I started researching. Surely I wasn’t the only person who wanted to switch their old school line voltage thermostat with a Nest! Unfortunately, a bunch of the solutions were on Nest’s old community site which had since been taken down. However, I was able to find out about a relay/transformer that according to the reviews should be able to bridge the gap between line voltage (240 V) and the typical low voltage setup used for modern thermostats like the Nest (24 V). The schematic for it shows the method for hooking it up to known thermostat wires.

aube-relay

The Aube Relay RC840T-240 does exactly that. It takes 3 wires carrying the line voltage (connected to Black, Blue, and Red) and then connects them out via 3 wires (R, C, W) carrying low voltage. This works to connect the line voltage wall heater with controls from the Nest system.

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After connecting everything up, I tested the Nest to see if it worked and low and behold! It worked like expected. The only thing left after wiring and testing the setup is to mount it properly. However, the relay/transformer does not fit inside the original electrical box so I will need to devise a workaround to get it to all fit within the wall up to code.

Read the Continuation here: http://blog.anthonyngu.com/2017/01/10/finishing-touches-installing-nest-w-line-voltage/