Dead short to pump

[Jon Mikesell]

My 30 year old submerged well pump seems to be dying. One side of the 220 cable measures 8 ohms and the other reads .5 ohm, measured at the switch. Needless to say, it blows a fuse whenever turned on. Before calling the well company, I'm going to make the same measurement at the well head. Are there any other tests I should run?

 

[Reach4]

I presume the breaker is off when you take the ohms measurement. Make sure it is a 2-pole breaker. If it is only a single pole breaker, then you would have a 115 volt pump instead of a 23o.

With the breaker still off, I would separate the contacts on the pressure switch with a bread clip or two (or use another hand insulator. Check to see which side of the pressure switch the short to ground is. The short is probably on the pump side, but it is easy to check before proceeding.

 

[Sponsor]

 

[Jadnashua]

It could be a chaffed wire, a corroded pressure switch, or even the shutoff switch has some corrosion in in. Or, it could be a bad pump or the wire going to it. You should be able to fairly easily verify the integrity of everything above ground, but probably not the wiring or pump without pulling it.

There are some fairly sophisticated test devices that can isolate the location of a wiring fault, but not something you would likely have or could rent economically. Simple meters can tell you resistances, but not locate a bad spot in a wire.

 

[Cacher_Chick]

It it a 240v pump? If so, is it a two-wire or a 3-wire pump with a control box? When measuring, what is your reference point?

 

[Jon Mikesell]

Thanks guys. Pump is 240v with two wires and a copper ground wire. Resistance measurements were made with reference to the copper ground.
Because one power wire is ok, I'm inclined to think the problem is a corroded 120v wire either underground between the house and the wellhead, at the wellhead, or down the well. I had a severe brass corrosion problem at the pitless 15 years ago or so. That electronic test device that Jadnashua mentioned would say where the short is in a minute.

 

[Cacher_Chick]

The ground wire should be bonded to the casing (if is is steel) and connected to the motor. You can disconnect the wiring at the well head to measure directly from there, which would rule out a problem between the switch and the well head.

 

[DIYorBust]

Congrats, you're getting a new pump!