"Samuel M. Goldwasser" wrote in message
...
Common (non-solid state/brushless) motors:

* Series DC motor, shunt DC motor, universal AC DC motor: Direction
determined by relative wiring of stator and brushes.

* Permanent magnet motor: Direction determined by polarity of DC (or
PWM etc.) input.

* 3 phase AC induction motor: Direction determined by phase relationship
of 3 connections. Swap any two pairs to reverse motor.


One more thing to add to this that hapened where I worked. I don't recall
the type of motor, but it was around 100 HP and had 4 sets of brushes and
was driven by a varitable speed drive. Two people changed the brushes and
said they did not touch the wires. It ran backwards. Several others looked
at it and could not determin why it was running backwards. I went up and
asked a few questions. I solved the problem for them. They had loosened
the plate that holds the brushes and rotated it some to make it easier to
replace the brushes. When they rotated it back, they had put it in the
wrong place. By rotating it back to the correct position it ran the correct
way.