The motor is often referred to as the heart of an ESP system because if the motor stops, everything stops. Also when something goes wrong with the motor it normally changes from a state of operating correctly to completely unusable – in other words it tends not to show signs of wear. Next to the pump, the motor is the second most important item in the ESP system.

Motor selection is based on expected pump loading and possible pump loading. It involves looking into the future to changing well conditions and if a VSD is used it often needs to be oversized to handle higher frequencies. However, there is a point where installing a motor that is too large is detrimental to both the motor life and the efficiency of the ESP system.

Motors come in single, upper, center and lower tandem sections. The diameter varies and this can have a large impact on the cooling of the motor. The general rule of thumb is that well fluid needs to move past the motor at a speed of 1 ft/s or 0.3 m/s to ensure proper cooling occurs,  however, most ESP design software calculates motor cooling.

Some items in the motor design need to include wire insulation (kapton, peek, etc.), temperature rating, metallurgy of the housing, standard or variable rated, voltage/amperage selection and pothead style. There are generally three types of potheads; plug in, tape in and direct connect. Each has advantages and disadvantages.