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Troubleshooting Residential Submersible Pump Systems

Dec 1, 2008 12:00 PM, By David Herres, Master Electrician

In the case of the pump system, it is decided to take measurements at the wellhead. The well cap is removed. The three wires at that point are frequently spliced with twist-on wire connectors, which can be removed to access test points. If not, the conductors can be cut with power locked out and later reconnected using silicone-filled twist-on wire connectors. Although it's found that voltage is present, a clamp-on ammeter reveals no current flow with the wires reconnected. Thus, an underground line fault is eliminated. Before pulling the pump, go back to the control box and take additional resistance and current measurements, referring to the information printed inside the control box.

With a good helper and power locked out, you can pull a pump-motor assembly in about an hour. Now is a good time to visually check the cable for abrasion or other damage. Separate the motor from the cable, and do meter tests to the cable to further isolate the problem. Let's assume the cable turns out to be in good condition. If the earlier clamp-on ammeter test had indicated excessive current flow — and there is no line damage — it looks like the motor has one or more shorted windings, is seized, or the pump will not turn. Before giving up completely on the motor, consider the possibility that the motor pigtail has acquired a short circuit, possibly due to lightning damage. This wiring harness has a plug-in connector right on the motor and can be unplugged after removing the protective metal channel. If that is not the problem, unbolt the pump from the motor, and see if the motor shaft will turn by hand. If it is seized, you must replace the motor. This is because it's a sealed unit; therefore, it's not possible to rebuild it. If it will turn, then you can conduct a brief dynamic test.

Another piece of advice is to make sure you have a good equipment ground connected. You should clamp the motor to a large, dry piece of plywood. Do not touch the metal case while the motor is energized. Fire it up very briefly, because it is designed to be run submerged in water for cooling purposes.

If the motor runs, there is the possibility that the pump has become sand bound. It is a simple matter to take it apart and clean it, reassemble the unit, and retest. You can inspect the pump impellers and replace them if worn or damaged. If it runs and meter readings are good, reset the pump a few feet higher so the problem does not recur.

Usually, the foregoing procedures will result in a successful repair. If not, you'll have to retrace your steps, and see if you made a false assumption or misread data somewhere along the line. It's also possible there is partial damage to the cable that did not show up during your visual inspection. This can be misleading and cause you to go around in circles. Another curve ball that may be thrown your way is when there are two or more faults. Finding and correcting one of them will not restore normal operation. The answer to both of these problems involves using patience, persistence, and perception. You have to go over the whole system, keep isolating stages, and apply logic to each one.

Beyond the basics

One mistake many beginning electricians make is they think they're going to find the problem in 5 minutes. If the above described procedure doesn't pinpoint the problem, then you'll need to turn to other troubleshooting techniques.

Suppose the readings at the well cap indicate there was no fault in the cable going down inside the well casing, and the pump motor was good. Ohm readings from the wellhead back to the control box — with wires disconnected at the wellhead and control box cover removed — indicate a short between yellow and black conductors. Then you know the fault is in the underground portion of the circuit, which is buried at a depth of 4 feet, for example. At this point, you know some digging is required.

Because backhoe time is costly, careful planning is essential. What is the minimum digging required to locate the fault? Can cutting the wire to take readings at various points along the cable be avoided? If you use the divide-and-conquer method again, it's possible to dig at the midpoint of the underground portion of the line and take readings to ascertain which half of it contains the fault. Then repeat this process by digging at the midpoint of the faulty half of the line — further narrowing down the problem segment. This limits the amount of digging you'll have to do to locate the exact point of failure. As for cutting the wire to take measurements, that is not necessary. Apply a voltage in series with a heavy load and use a clamp-on ammeter to perform the test.

You might also consider what some view as an even better method — one that involves a more sophisticated test and less digging. Take ohm readings from both ends to locate the short. If the reading at the house is double the reading at the wellhead, then you know the short is one-third the distance, or about 166 feet, from the well.

Herres is a licensed master electrician in Stewartstown, N.H. He can be reached at electriciansparadise@hughes.net.

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