As I understand it, most three prong electrical chords are have a hot wire, ground, and neutral terminals (for extra precautions). My swamp cooler motor cord has four prongs as shown here:

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What is the need for the fourth terminal? It seems to me that most, if not all, cords for swamp cooler motors have three circular terminals and one flat terminal as shown above. Why are these terminals shaped as such? Is there any advantage to having their shapes this way?

1 Answer 1


That looks like an Adobe P2-911 plug and it is proprietary. There's another version Adobe made (I believe it's for the 230v motors) that has a 5th round pin. The flat bladed terminal is for keying the connector so it can't be plugged in upside down. You should have a 115v cord with 2 hots - one for high speed and one for low speed, 1 neutral, and 1 ground.

  • 1
    Yep, it's to accommodate multi-speed motors.
    – iLikeDirt
    Commented Jun 29, 2014 at 3:57
  • 1
    Doesn't the arrangement of the 3 round prongs make it impossible to plug in upside down anyways?
    – Paul
    Commented Jun 29, 2014 at 15:05
  • @Paul - On the 4 prong plugs, yes. The 5 prong version is arranged in an "X" shape that is symmetrical with the exception of the flat blade.
    – Comintern
    Commented Jun 29, 2014 at 15:34
  • I want to be able to use this motor for a different application. Would it be possible (safe) to hook it up to a standard 3 hole wall outlet?
    – Paul
    Commented Jul 4, 2014 at 18:33

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