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circuit. This PLC circuit implementation does not provide low-
voltage protection, since the interlocking does not use the physical
inputs of M1, S1, and S2.
Figure 5.3 - PLC implementation of the circuit in Figure 1
If low-voltage protection is required, then the starter’s auxiliary
contacts or the overload contacts can be programmed.
If the auxiliary contacts or the overloads are used as inputs, they
must be programmed as normally open (closed when the overloads
are closed and the motor is running) and placed in series with
contact 1000 in line 3 of the PLC program.
If the overloads open, the circuit will lose continuity and M1
will turn OFF.
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