When designing a thermostat, a relay must swtich a 24V AC signal to call for cooling / heat / fan etc.
Industry standard thermostat wire color code used for most systems:
White. The white wire connects to your heat.
Yellow. The yellow wire connects to your compressor.
Green. The green wire connects to the fan.
Orange. This wire connects to your heat pump (if applicable).
Red (C). The Rc wire connects to the cooling system.
Red (H). The Rh wire connects to the heating system. This wire may be red without an “H” attached, in some cases.
Blue. The blue wire on the thermostat is the Common or “C” wire.
Is there a rule of thumb to determine the minimum current rating of a thermostat relay? I see many relays for raspberry pi that can accommodate 10 Amperes and would like to know if currents are typically under 1A.
Best Answer
Well, the entire system tends to be powered by a bog-standard 25VA or 40VA transformer at 24 volts. That means total amperage available to the system is either 1.04A or 1.6A.
So I think a 10A relay is pretty safe design choice.