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Thread: Submersible pump motor keeps failing

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  1. #1

    Default Submersible pump motor keeps failing

    I have a 1hp 2-wire 240V submersible 4" pump installed in a PVC-cased 6" well. It was installed 6yrs ago. The original pump/motor was a red jacket grizzly with Franklin motor. After 3yrs it failed (locked rotor) and when I pulled it out the case was visibly corroded with holes in it. The pump itself looked fine

    3 year old well pump motor case corroded so badly it seized up?

    I replaced the Franklin with a same-sized Grundfos which operated fine until I turned it on last weekend for the first time since winter. No water. I pulled it out and it also had a locked rotor and the same case corrosion.

    3yr old SS pump motor corroded AGAIN

    The well is connected to a lawn irrigation system and has plenty of sulfur that you can smell and see the residue. I measured the pH at the top of the water table and it was 7.3.

    After seeing pics of the corrosion the pump guys thought this should be posted in an Electrical forum as well.

    I really really really need to keep this from happening again.

    Pics of the 3-yr-old failed Grundfos:

  2. #2

  3. #3


    Maybe some of the guys who are familiar with boats and sacrificial anodes can explain what's happening... I'm still trying to figure out why fire ants are attracted to electricity.. .they keep congregating in my plugs and switches in my storage trailer.

  4. #4
    Electrical Contractor/Instructor jwelectric's Avatar
    Join Date
    Jun 2007
    North Carolina


    Something is causing a high current draw on the motor.
    It could be that the conductors supplying the motor are too small, sediment on the impeller or any number of other things

  5. #5


    I've seen this type of thing happen to motors that their electrical supply such as too small of extension cords caused them to heat up... also the same problem with corroded or loose connections in the switch box. So, maybe check your wiring to the well pump.... it's the only guess I've got. If it happened only one time then I'd suspect the motor. Since it is repeating itself with new pumps I'd look for something else causing the problem. Something is making the pump work harder than it should... if it ain't mud or sand then it has got to be in the electrical supply. I had a friend who's well pump kept burning up relays and having problems. We found a wire with broken insulation and someone had been putting on the wrong kind of relay. Taped up the skinned spot on the wire and put in the right kind of relay and no problems since.
    Last edited by Randyj; 04-13-2011 at 07:03 AM.

  6. #6


    I don't think it's mud/sand. The water from the sprinklers is good and I don't get clogs very often. No signs of mud/sand when I pulled out the pump.

    The wire from the the panel to the pump is all 12AWG. There is a switch box on the side of the house, and the wire goes underground in conduit between the switch box and well head.

    I will inspect everything I can get to for loose connections and damage. For what it's worth, I haven't had any relay problems that I'm aware of and no problems tripping breakers.

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