Thermostat wiring question
Technically no. That bare wire is for grounding (bonding) purposes only. Never to be used as a normally current carrying conductor. One concern I will mention is, what if someone in the future works on that wire? They will most likely assume it’s a ground wire, and not know that there is actually voltage present on it. True 99.9999999999999% of the time 24 volts isn’t going to harm you, but it could. Remember, it’s the amperage that can kill you…not the voltage.
Just because you can, doesn't always mean you should