I have been an electrician for 30 years. Much of the time I have worked on commercial jobs---schools, office bldgs, hospitals---and also have been involved with small sawmills and the like. The latter is the extent of my industrial experience until 3 years ago when my company took on the maintenance of a company which has concrete and asphalt batch plants and large rock crushing operations.
That means that all my career I have seen electric 3 phase motors with 3 wires running to them. What few motors were large enough to need soft start starters were reduced voltage type, meaning they also had 3 wires feeding the "peckerhead".
The company who has the rock crushers has a few big motors with soft starts---all reduced voltage except one which I now know is prob. wye start/delta run (or possibly part winding start??) because it has 6 leads leaving the starter.
For that reason when I was told we were running 6-3/0's to this fire pump when we had just run 3-250 MCM to feed it's controller I asked why it was 6 wires and why so big. It was my first experience ever running more than 3 wires to the motor and thus made me curious.
It is very clear now that this allows the motor to be fed one way for start up (by the 3 contactors in the controller swapping leads around---temporarily re-wiring the peckerhead if you will) and another way for run (by the 3 contactors swapping the 6 wires around to being 3 sets of parallel runs to carry the 180 amps FLA of the 150 HP motor).
We ran 6-#1 Copper THHN's to the motor today, and I have a clear mind about it because I now know that 3 of the "half size" wires (#1) will be adequate to carry the less than FLA start up current while it is "wye", and that parallel runs of #1 will carry the 180 Amp load when it is on "run" and in the delta configuration.
You're never too old to learn in this trade.
