What wire size is needed to 125 amp load for 340 feet?

== == 125 Amps is a very heavy current load for a household circuit so this 340 ft run may be for some industrial plant or equipment... You really should know how to handle wiring size calculations already before you install that kind of stuff.

<><><> To do a proper calculation, working voltage is needed, whether it is single phase or three phase and whether the wire is copper or aluminium. Single phase - 125 amps at 120 volts, copper wire #3/0, 125 amps at 240 volts, copper wire #1 Three phase - 125 amps at 480 volts, copper wire #4 ----- As always, if you are in doubt about what to do, the best advice anyone should give you is to call a licensed electrician to advise what work is needed. Before you do any work yourself,

on electrical circuits, equipment or appliances,

always use a test meter to ensure the circuit is, in fact, de-energized. IF YOU ARE NOT ALREADY SURE YOU CAN DO THIS JOB

SAFELY AND COMPETENTLY

REFER THIS WORK TO QUALIFIED PROFESSIONALS.