NEMA Reversing Contactors
The NEMA reversing contactor reverses the motor's direction without any need for an additional switching device. The reversing contactors are designed to handle high-current loads found in industrial and commercial applications where reliability is paramount. They meet rigid safety and performance standards established by NEMA (National Electrical Manufacturers Association).
The primary purpose of NEMA reversing contactors is to alter the phase sequence for motors. This helps reverse the direction of motor rotation when needed or desired. When the forward contactor carries current to the motor, it puts together a certain phase sequence that makes the connected motor function in one particular manner—namely, it causes it to rotate in a forward direction. When reverse carrying current to that very same motor (a situation achieved when the 'reverse' contractor-carrying finger sets are closed), another set of phase-angle voltages results and causes that very same motor to turn around and function in the opposite fashion—it turns backward.
NEMA reversing contactors rely on both electrical and mechanical interlock mechanisms to operate safely. The former physically prevents simultaneous closure of the two contacts, which would result either in a short circuit or in damage to the motor. The latter relies on auxiliary contacts and achieves the same end by making it impossible for both contactors to carry current at once. These provably enhance the dependability and safety of motor control systems.
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