Thermostat Common and Earth Ground
Common question these days. I've bought a new WiFi enabled thermostat which requires a C (Common) wire. My current connections only include R, G, Y, and W, no C. I saw a YouTube video from HoneyWell showing how to move the G (Fan) wire to C at the transformer, and use the G wire as C, however, they noted this only works for Gas furnaces because they automatically enable the fan. In addition it will disable the ability to manually turn the fan on. I do have a gas furnace for heating, but I have an electric A/C for cooling, so I don't know if this is even an option for me.
I looked at the possibility of adding another C wire and running it through the wall, but it's not a practical option. There is no attic space above and I'm in a condo on top floor so can't run it below either. To run a wire I would have to put holes in the drywall in various places. I would rather not.
Anyway, that's the background, here's the question, actually 2 questions. 1) The voltage from my R wire to the other wires (G, Y, and W) shows 27.5V, I thought it's supposed to be 24V, is this a problem? 2) There is a 3-way light switch right below the thermostat that has an Earth Ground wire in the box. I measured the voltage from the Thermostat R to the earth ground and it was 28V. Is there any reason, other than it's against code, that I can't replace the thermostat Common with the earth ground? I understand that earth ground is for safety and is designed to not have current running through it, however I really doubt the small amount of current the thermostat pulls will lower the safety of my home's wiring. I also understand that if the transformer is ever replaced this quick fix may not work anymore. Other than these things, are there any other considerations?