thermostat controls help

[buffer72]

Hi all
Can someone tell how electrical power is supplied to thermostat controls of HVAC equipment?
Who normally supplies this power?
Any help or direction of reading material is greatly appreciated.

Sincerely

 

[simsd]

It depends on what you are talking about. I assume you are talking about package units. If so then generally there is a transformer built into the unit that goes to a terminal strip. The standard designations on the terminal strip are as follow:

R - 24 V
C - Common leg of 24 V
G - Fan
Y - Cooling
W - Heating
O - Reversing valve if it's a heat pump.

If it's not a package unit, then generally the controls contractor will provide whatever transformer(s) may be required. Depending on the situation (complex) a 120V circuit may need to be provided if it's a more complex control situation. If not then many times, the contractor will step down power from the main incoming power to the unit.

 

[KiwiMace]

Yes, more generally speaking, they are usually powered from the device that they control.