Heat strip lock out on generator power


New member
Manassas, VA
The following quote was originally posted here: http://forums.mikeholt.com/showthread.php?t=104381

I install a relay that locks out the emergency heat (the heat strips)(this can be done by a relay powered by generator only breaking the control wire for the heat strip relay from the t'stat) so the load is compressor/fan only. If it gets cold enough that the compressor locks out their SOL. Usually try to talk them into a small gas wall heater for emergency heat.
You made this post about 10 years ago, and it doesn't look like you've posted in a few years. Still, if this message finds you I could use some help. When I installed generators I would always use a 60-100 amp contactor to manage the load of heat pump systems. Generally the heat pump and blower would operate, depending on available capacity, but if the strip heat comes on the whole system will drop out. I know its preferable to just lock out the strips, since the heat pump will still provide some heat, even when its very cold outside. I never did that because it requires getting a wire from the ATS to the furnace, which usually isn't feasible. The company I work for now has just developed a wireless device designed to interrupt 24VAC control circuits. My question is, which stat wire am I looking for to just drop the strips? Any help is appreciated.


EC, Westchester, New York NEC: 2014
Hawthorne, New York NEC: 2014
I think many of those posters are long gone. As to your question, I think it would depend entirely on the heating equipment you are working with. I don't know, but I don't think there would be a wire on the room thermostat for it. Likely today it's one job of the controller. A sensor senses outdoor temps and decides when to switch from heat pump to resistance heat.

Let's see what others have to say.



Master Electrician Electric Contractor Richmond VA
Henrico County, VA
Electrical Contractor
My question is, which stat wire am I looking for to just drop the strips?
If memory serves, I believe it is the white wire.

Red = hot
White = heat
Green = fan
Yellow = AC comp
Orange or brown = HP rev valve
Black or blue = common


Electron manager
NE Nebraska
Kinda. Connect red and white together and you turn on the heat. It doesn't control where it comes from, heat pump or resistance heaters.

typical heat pump system W terminal is backup heat, W2 can exist and can be a second stage of backup heat, or tie them together if controller is only capable of single stage.

Y terminal is the compressor and depends on state of the reversing valve as to whether or not it will be in heat or cool mode.

So to disable backup heat you interrupt W terminal.

To disable compressor (heat or cooling mode) interrupt Y terminal.

Multistage compressor will have Y1 and Y2 terminals.


Senior Member
Field coordinator/ technical support
Manufactures seem to vary on how they control the backup heat (heat strips) sometimes it's W, sometimes W2, and sometimes E. If there is no wires terminated on W2 or E, it would be safe to assume W is the aux heat. If there is a wire on W2 or E, then that is probably the aux heat. Most of the residential permanent generators now have load shedding capabilities driving a 12 vdc relay to directly ( in the case of low voltage, low current loads) or indirectly control larger loads through a contactor. With the newer gensets, they have internet connectability to toggle these loads off and on while showing actual load.


Senior Member
New York
Master Elec./JW retired
If it's wireless/wifi mount right at the strips and interrupt the control wire to the contactor, see wiring diagram on side of unit.