For many decades my century old home employed a mechanical thermostat that was electrically connected to the heating system via one pair of wires which would close a circuit to turn the heat on or open the circuit to turn it off.
Forty years ago I installed a programable thermostat to perform the same function but with the added feature that I could program set back functions to change the temperature settings for designated periods of time.
A close evaluation of the electrical circuit in question yields the following result:
The control circuit is a 24VAC ungrounded circuit.
This is what we in the electrical control industry call, "a dry contact".
To which terminals on my Nest Learning Thermostat should I connect the two wire control circuit?
