1

I have a well with a 1.5 HP pump. The pump is rated for 240V input. At the moment, the only nearby available power is 4-wire 208Y 3phase. I am considering connecting two of the three phases to the well pump, so it receives 208V where it is expecting 240V.

To what extent, and by what mechanism, will it hurt the pump if it is powered by 208V instead of 240V? Are there warning signs I can observe (like something electrical I can measure, or something I can observe about the flow of water) that would indicate whether this lower voltage is causing problems?

More generally, when an AC motor says it's rated for a certain voltage, without specifying a range, how tight is that calibration? Like, what is the "probably not much worse" voltage range? My intuition says "ohh eee ah around 15%" but I'm realizing I have no actual basis for that sentiment.

Diogenes Creosote
  • 241
  • 2
  • 9

1 Answers1

3

The 1.5 HP motor is built to draw a specific amperage at full load at 240V. Because power equals voltage times current, a lower than rated voltage will draw more amps through the motor. So if your supply is 208, your current will increase by a ratio of 240/208, or about 15%. Low voltage/high amps is a common failure mode for hand power tools being used with undersized extension cords.

If the motor is under a light load, you will likely never notice. But if it is running at full load, you might find it overheating, tripping overloads, or just generally failing early.

Diogenes Creosote
  • 241
  • 2
  • 9
Tiger Guy
  • 7,376
  • 10
  • 22