Alltrax SR48300, Operator'S Manual, Page: 9 / 32

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Controller Amperage F/R Size
400A or less Stock/HD
450A to 650A Heavy Duty/Change-Over
Contactor
650A or more Change-Over Contactor
The forward/reverse switch is an often overlooked part of the
upgrade process. In a series motor, all of the motor current will
pass through the F/R switch. An undersized F/R Switch is as bad as
an undersized solenoid or small wire gauge.
For higher amperage controllers (>600A), it is suggested that a
change-over contactor set up be used. These are large enough to
handle the higher currents without over heating the contacts and
they provide the user the ability to change direction by flipping a
switch.
F/R Switch
Change-over contactors are multiple contactors bound together
that allow the user to change the polarity of the voltage going to
the motor thus reversing direction. It works exactly the same as the
manual F/R switch, except that it uses coil drive contactors. See the
installation drawings for how to wire up a change-over contactor.