pressure switch wire

Jul 06, 2008 20 Replies

Okay, they didn't oversize that.

Full Load Amps. And for sizing the wire and the contactor, knowing the Locked Rotor Amps (LRA) can be important too - every time the motor starts it is drawing LRA while it is at a stand-still and it drops off to FLA as it spins up - a half second to a second.

It's best to figure the voltage drop at the LRA which is worst case, so it isn't starting under brownout conditions every time.

And read the book for the well pump - the motor maker may have their own rules for wire sizing and other installation details - no follow, no warranty. If National Electrical Code, Local codes, or the motor makers instructions do not agree, the most conservative one applies.

And my book with all the formulas is out in the truck - so I didn't forget you, I'll look it up in the AM. But for a rough guess I'm going to start the math at 1/0 AL wire, and that's going to need

1-1/2" conduit. (And that would be right on the edge for fill. Might have to go to 2")

If it's single phase, a simple dedicated purpose contactor like they use in an air conditioner is sufficient. You don't need overload heaters or phase monitoring on a single-phase motor.

The one thing that might be helpful is a Warrick Controls water-flow monitor that trips the well off if it runs dry. It's a simple sense probe in the output pipe that looks like a sparkplug, and if the water level in the pipe drops...

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