Circuits
38 Anti-Plugging With Zero-Speed Switch
If a forward-reverse circuit is not designed or rated to withstand the severe overcurrents and torques associated with sudden reversals in direction, a zero-speed switch wired normally closed can provide this function.
Once the zero-speed switch is attached to the shaft of the motor, its normally closed contacts are then wired in series with the opposite directions coil. In this manner, they act similar to the electrical interlocks but provide an extra delay function while the shaft of the motor still spins.
This means that even after the stop button has been pressed, the reverse coil cannot be engaged until the motor has stopped rotating in the forward direction, and vice-versa. Once the motor has come to a rest the zero-speed switch contacts will close and the motor can then be engaged in the opposite direction.
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A sharp and fast rise in current over a short period of time (fractions of a second) where the value of current is far greater than the nominal line current.
A switch that is activated by centrifugal forces and is attached either directly or via a belt to the shaft of the motor.
A contact that under normal conditions has continuity through it. When the contact changes its state it interrupts the flow of current by opening its contacts. Can be associated with pushbuttons, pilot devices or magnetic contactors.
In electrical terms, refers to a connection where current has only one path to flow.
Loads connected in series will have the the same value of current flowing through them, and share the total voltage between them. Switches and overcurrent equipment is connected in series with equipment to control and protect it.
Normally-closed contacts used in forward/reverse control circuits that prevent both directions coils from being energized at the same time.
