Greenhouse ventilation motors, thermostat, and wiring

Discussion in 'Electrical Forum discussion & Blog' started by TJanak, Feb 28, 2011.

  1. TJanak

    TJanak New Member

    Messages:
    154
    Location:
    South TX
    I rent space in a greenhouse that has two ventilation fans, 1 HP motors each wired for 240V. This year one motor was bad so it was partially disconnected (one leg) and the other was turning at a much slower speed and I only got 68V across both legs at this motor. These motors are controlled by a Dayton line voltage thermostat.

    Opening up the fusebox, I could not figure out the wiring. Looked like they were wired in series with the thermostat stuck in there somewhere. I took it all apart and started over, with two legs from the fuses going to the thermostat and then on to only one fan. It now runs correctly.

    Problem is I would like to hook up the other fan but the thermostat is rated 8 amps at 240V. These motors are each ~6 amps. I know both fans used to run correctly (simultaneously) several years ago. Were they simply running 12 amps through the thermostat or could they be hooked up in a way that the thermostat could control both fans without full current going through the thermostat?

    I don't see how but figured I would ask.
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,824
    Location:
    New England
    You could use the thermostat to control a power contactor...just make sure the contactor contact rating is sufficient for the motors being used. The coil of that should easily be within the range of the thermostat's ability.
  3. dlarrivee

    dlarrivee New Member

    Messages:
    1,172
    Location:
    Canada
    It would probably be just as cheap to buy a second line voltage thermostat...
  4. TJanak

    TJanak New Member

    Messages:
    154
    Location:
    South TX
    I guess they must have both been run through the thermostat, even though it would be overloaded. Two thermostats would work but it would be better if both fans turned on and off at the same time. Thanks.
  5. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,293
    Location:
    Cave Creek, Arizona
    The description is confusing. IF the motor was bad and one leg was disconnected, why would you now try to resurrect it? A 240v thermostat should have had 4 terminals, but you imply it only had one line going through it. What was connected in series? The motors? If so, disconnecting the wire from one of them should also have also kept the other one from working until it was rewired.

Share This Page