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Thread: Heat strip lock out on generator power

  1. #1
    Join Date
    Aug 2018
    Location
    Manassas, VA
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    1

    Heat strip lock out on generator power

    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.

  2. #2
    Join Date
    Jun 2003
    Location
    Hawthorne, New York NEC: 2014
    Posts
    3,837
    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.

    -Hal

  3. #3
    Join Date
    May 2005
    Location
    Richmond, Virginia
    Posts
    23,377
    Quote Originally Posted by Captn View Post
    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
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

  4. #4
    Join Date
    Jun 2003
    Location
    Hawthorne, New York NEC: 2014
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    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.

    -Hal

  5. #5
    Join Date
    Dec 2007
    Location
    NE Nebraska
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    37,928
    Quote Originally Posted by hbiss View Post
    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.

    -Hal
    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.
    I live for today, I'm just a day behind.

  6. #6
    Join Date
    Jul 2007
    Posts
    3,103
    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.

  7. #7
    Join Date
    Mar 2003
    Location
    New York
    Posts
    1,244
    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.

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