What is the Difference?

 Submersible pumps, the kind of pump that goes in your well or cistern, are available with two wire motors or three wire motors.  There is also another ground wire which is not counted, so if you look at the pump the actual number of wires will be three or four.  The two wire pump will have two black wires and one green ground wire.  The three wire pump has a black, red, yellow and green wire.

You are probably thinking, “That’s nice, but what is the difference to me?”  The main difference is the three wire pump uses a separate control box which includes a capacitor and relay to start the pump.  The control box is located inside your house or pump house.   The two wire pump does not use a control box.  Everything is built inside the motor of the pump.  All motors larger than 1 ½ HP are only available in the three wire version because you need the control box to start the heavier motors.  Most residential pumps are smaller horsepower.  Our top selling pump is just ½ HP.

Many years ago we sold mostly three wire pumps.  We believed that having a separate control box above the well would sometimes save people the time and expense of pulling the pump when they experience a problem.  If the problem is in the control box it is a simple and relatively inexpensive fix to replace the box, as opposed to pulling the pump and replacing the motor or whole pump.  This is the main advantage of the three wire pump.  Then, probably 25 years ago, a local plumbing contractor insisted he had far fewer problems with two wire pump systems.  We slowly shifted to selling more two wire pumps and our experience seemed to agree with the contractor’s observations.  Also, two wire pumps are less expensive, the wire used to install them is less expensive and the installation is easier because you do not have to wire through the control box.  Of the pumps we now sell, at least 90% of them are two wire.


  1. steve

    Excellent post! Thank you very much for explaining the differences and the advantages/disadvantages of each system.

  2. Chuck Owens

    Sweet, you’ve answered a problem I was having…I wondered why there was no yellow wire on the pump, someone has put in a two wire pump and left the control box for a three wire pump…two wire pump can’t be wired into the control box I discovered.
    I love learning new stuff

  3. sNEAKYX16


  4. Hi sNEAKYX16, Not sure who you intended this question for, but the answer is: it depends. The task itself is not hard. You need to replace it with a junction box. The tricky part has to do with the length of the existing wires. If they are long enough to remove the control box and insert them into the junction box, then the task is easy. If not, that may be a problem more difficult to solve.

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