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@WinterDeere, I have a fondness for older machinery. I do think that the comment he wrote about temperature dictating duty cycle is spot on.
To unpack that a bit, these days different motors are designed with different grades of insulation, and different temperature ratings. E.g.
There is a bit of a quirk to the NEMA motor ratings in that different intended uses have different service factors (allowed time at maximum current draw). This differs from international norms (IEC). (
Full review here for the curious.) However, nearly every modern motor of typical HP that I have seen is at least 100% service factors/duty cycle. Whether the motor will last at 100% is a different call, and gets into the use, and environmental conditions.
Side note: inverter rated motors have higher insulation levels, and often design elements such as square wire, non-random windings, different rotor construction, to function efficiently at frequencies other than 60Hz. (Or 50Hz) Speaking of efficiency, there are also grades of efficiency in motors, and if the motors is in frequent / constant operation, moving to a premium efficiency motor will save energy, and often a short ROI on the added cost.
Back to well pumps; on any given well, one wants to size the pump smaller than the drawn down to keep the pump from running dry, and then large enough to service the expected consumption in a reasonable time period, but short cycling a pump is not desirable which is why there are storage tanks, but neither is a low flow long run, as the submersible pumps need the cooling as
@steve tym pointed out, but also due to energy consumption. If you have a pump running against some restriction, like a partially open valve, that is wasted work and energy.
In my experience, pump lifetime gets into usage hours, how it is used, water quality, and especially the presence of foreign matter, e.g. sand, in the water. A pump that gets slowly sandblasted is not going to have a long life time.
All the best, Peter