VD question/issue for well pump motor

[sw_ross]

A vault for the pump is located 280’ from the house where power comes from,
The pump motor control box and pressure tank are going to be installed in the vault.
The well is 300’ deep. The well driller dropped #10 AWG wire to the pump motor at the bottom of the well. The pump motor is 3 HP, 240V, 1-phase.

Regarding voltage drop we were told we only needed to concern ourselves with the distance to the vault and not past the control box.

In my mind vd needs to include the full distance to the load (pump motor).
Am I missing something?

 

[winnie]

Unless there is an energy code that applies, voltage drop is only a recommendation, not a requirement.

The issue with voltage drop is 1) efficiency (losses in the wire) and 2) functionality of equipment.

Most residential wells run infrequently, so straight up efficiency is rarely a significant cost issue.

If the voltage drops too much, then the motor might not be able to start reliably. This is a real concern since motors draw so much current on startup. IMHO voltage drop needs to be considered all the way to the pump, but it is the pump installer's concern for a portion of the run. So the well driller should say to you 'we need this much voltage with this much drop to the vault', and your responsibility ends at the vault. The pump installer should understand the voltage drop limits that the equipment can tolerate reliably.

It is possible voltage drop may function as a resistive soft start and actually _improve_ motor life, and possibly in the installer's data there is both a minimum and maximum voltage drop range. I would hope that these pumps are designed with the expectation of significant voltage drop.

-Jonathan

 

[ptonsparky]

Franklin Pump has recommendations in their manual for wire sizing to compensate for VD. I would not use less if you want a valid warranty.

 

[fastline]

A vault for the pump is located 280’ from the house where power comes from,
The pump motor control box and pressure tank are going to be installed in the vault.
The well is 300’ deep. The well driller dropped #10 AWG wire to the pump motor at the bottom of the well. The pump motor is 3 HP, 240V, 1-phase.

Regarding voltage drop we were told we only needed to concern ourselves with the distance to the vault and not past the control box.

In my mind vd needs to include the full distance to the load (pump motor).
Am I missing something?

Just absurdly wrong advice. Full trip distance. I do a LOT of pump work. Some of this depends on what that pump is expected to do in it's life. 3HP across the line hits is very likely to kill the spline coupler eventually due to the violent startups.