Does running a submersible pump under low voltage have any effect on the pump itself?

AC motors operated under low voltage conditions (say, due to line losses in a long wiring run) pull more amps and heat up more. The good news is that a submersible deep-well pump

has its electric motor at the bottom, below the inlet, so the motor is always submerged and cooled by the well/ground water which is usually pretty cold. (The pump impellers are above the intake screen in the middle).

So, although the motor will heat up more, it probably won’t effect its life much because it can dump that heat into the water around it.

Most household wire sizing can be done by just following Table 310-16 and its footnotes in the National Electric Code (short version: 14-gauge for 15 amps, 12-gauge for 20 amps, 10-gauge for 30 amps). Deep well pumps due to their medium to high amp draw, distance down the well and distance from the house are one load to always use a voltage-drop calculator for. If you drop more than 5% of the line voltage in the round-trip wiring, you should go to the next larger conductor.