On Sun, 6 Jul 2008 12:24:46 -0500, "Karl Townsend"
wrote:

For the power wire you need BIG wire to avoid voltage drop and keep
the pump motor happy for a long time - but there are a few other
questions before I can answer. Is the pump 240V or 480V? 1Ph or 3PH?
FLA? How deep is the pump, and did they oversize that line?

Its a 240 volt 1 phase 5 hp. pump. Three #8 wires down the hole 180 feet.

Okay, they didn't oversize that.

Don't know what you mean by FLA.

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.

This pump, like all submersibles, is sort
of a 2 1/2 phase unit with the control box putting some capacitance and
power on the third leg. So, what size AL wire and ground? How big a conduit
will I need?

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")

One more question, what size motor contactor?

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...

-- Bruce --