I'm looking to upgrade the thermostats in my apartment to ones which I can control programmatically over WiFi.
I opened up one of the old thermostats and discovered I have the classic "C-wire" problem.
Digging around behind the wall I discovered two twisted pairs coming out of the same jacket as the other thermostat wires (blue and white, brown and white).
Hoping to identify the C wire I busted out the oscilloscope and measured the voltage from the R wire to each of the four unused wires.
In all cases the voltage was 36V pk/pk and 17V RMS. Neither of these values is the 24V I was expecting for the C wire.
Is my measurement methodology incorrect? Are these the expected results? Can I purchase and install smart thermostats using any of these three links as the C wire? If not C wires, what are these?
Unfortunately I do not have access to the furnace end of the wiring.