This is a different tack, but the issue could be a poor motor selection for the pump. The short answer is that the pump will attempt to draw whatever
power that the piping
system allows it to. If this draw is greater than the motor’s output, it will burn out the motor.
The long answer: The pool’s recirculation pump is probably a centrifugal pump which will operate only under specific set of flow and corresponding
system pressure (head) conditions. These conditions are graphed as flow rate vs head to generate the pump’s “pump curve”. The flow rate and pressure
drop (calculated by analysis of the
system) determine the “operating
point” on the curve. The
power required to move the water through the
system and operate the pump can be readily calculated from the flow rate, head, and pump efficiency, the latter of which varies with the flow rate and head. After one calculates the required horsepower, the horsepower is rounded up to the nearest standard motor size.
Usually, pump vendors include lines of constant horsepower superimposed on the pump curve to aid in the selection of the motor size. More often than not, one motor horsepower will be entirely above the pump curve, and one or two lower horsepower motors will intersect the pump curve such that part of the motor
line is above the pump curve and part is below.
The necessary condition is that the motor horsepower be above the operating
point on the pump curve so that the motor is not overloaded, and this is where a problem can occur. Usually, the person buying the pump will specify that the motor size must of a size such that the motor is never overloaded regardless of the operating
point on the curve (this minimizes the impacts operating errors and other
system failures). However, there are cases where the pump buyer will look at the operating
point and see that a smaller (and less expensive) motor will work. And this may be fine provided that there in no way for the pump to operate at conditions elsewhere on the pump curve, at the high flow – low head end of the pump curve. And this can be caused by having the flow throttled too little, operating in a bypass
line with no flow control, operating at too high of a flow rate, or replacing the pump impeller with an impeller that is larger than the original (creating a bigger pump curve outside the motor range).
Joe