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2-Wire Versus 3-Wire Well Pump Motors

Most 4” submersible well pump motors used in residential applications are available in 2-wire or 3-wire configurations. The ground wire is not counted in the terminology.

2-wire motors have two black and a green wire. ---- ---- ----

3-wire motors have a black, red, yellow, and a green wire. ---- ---- ---- ----

The starting components for a 3-wire motor, including start capacitors, run capacitors, relays, and thermal overloads are contained in a control box above ground. The starting components of a 2-wire motor are built into the motor, which is mounted to the bottom of the pump, deep in a well.

Adding the starting components to larger submersible motors is not feasible. Therefore, 2-wire motors are available only up to 1.5 horsepower and 3-wire, single phase motors are available up to 15 horsepower.

So, your question may be: which one is right for me?

2-Wire Pros

easier to install

•submersible wire is lighter and may cost less

•internal components are sealed in motor, not exposed to the elements, and less likely to oxidize and fail

2-Wire Cons

•if starting components fail, the motor must be pulled and replaced

3-Wire Pros

•failed starting components can be changed cheaper and easier

•greater starter torque

3-Wire Cons

•starting components are exposed to above ground elements, and more likely to oxidize and fail

For most residential applications the preference of a 2-wire versus a 3-wire motor is usually up to the installer and homeowner. Under 1.5 horsepower, a 2-wire motor can be recommended by some installers due to the ease of installation, reduced maintenance, extended life of starting components, and cost advantages. On the other hand, some installers may recommend a 3-wire motor due to the fact the individual control box components or the entire box can be replaced in less than 45 minutes. Flip a coin or, better yet, ask your installers opinion. Their local knowledge may be a key factor in your choice of a 2-wire or 3-wire motor.

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