Motor Control¶

Classic Start/Stop circuit with seal-in relay and overload protection.

Ladder Diagram¶

Rung 0: Start/Stop circuit
    ──[ I:0/0 ]──[ B:0/0 ]──[/I:0/1 ]──[/I:0/2 ]──( B:0/0 )──
      StartPB     SealIn     StopPB    Overload    SealIn

Rung 1: Motor output
    ──[ B:0/0 ]──( O:0/0 )──
      SealIn     MotorOut

Rung 2: Run indicator
    ──[ B:0/0 ]──( O:0/1 )──
      SealIn     RunLight

Logic¶

(Start OR SealIn) AND NOT Stop AND NOT Overload → SealIn

I/O Assignment¶

Address	Description
`I:0/0`	Start push button (NO)
`I:0/1`	Stop push button (NC in field)
`I:0/2`	Thermal overload relay (NC in field)
`O:0/0`	Motor contactor
`O:0/1`	Motor running indicator light
`B:0/0`	Seal-in relay (internal)

Note

The Stop and Overload inputs use XIO (examine if open) because they are wired as normally-closed contacts in the field. This provides fail-safe operation — if a wire breaks, the motor stops.

Tip

Open examples/motor-control.plcproj in PiPLC to try this program.

Variant: Dual Start Buttons¶

Use parallel branches for OR logic with two start locations:

     +--[ StartPB1 ]--+
--+--|                |--[/StopPB]--[/Overload]--( SealIn )--
     +--[ StartPB2 ]--+
     |                |
     +--[ SealIn   ]--+

See examples/dual-start-motor.plcproj.