Electric motor magnetic contactors are for
starting electric motors. Magnetic means that a
small electro-magnet is used to actuate the
contactor as an On-Off switch. This design
allows for safely switching large amounts of
motor current (amps) using low voltage control
circuits instead of manually operating a large
switch. Note in the image the L (line input
power) terminals and T terminals (motor
leads). The contactor shown is a 3 phase
contactor for starting 3 phase induction motors.
A single phase contactor operates indentically
to the one shown, but has fewer line and load
connections. Also at the top in the rear, are
the control voltage leads that energize the
small electro-magnetic coil assembly inside the
contactor. The far right of the contactor has
space for auxiliary contacts but none are
installed on this contactor. Auxiliary contacts
are useful for many reasons. Example is lighting
a warning light when the motor is running.