Electrical & Automation · Free tool
Explore PLC control logic
Operate a motor starter, control a tank level or explore a timed traffic-light sequence. Change the inputs and follow the highlighted ladder logic from the field signals to the outputs.
Each scenario starts running when you open it. Use the arrow keys to move between tabs.
Loading motor controls. The motor starts stopped; START, STOP and overload RESET become available when the page is ready.
The theory
How the motor circuit works
- Normally open (NO)
- A contact that only conducts when operated. START is NO: current flows only while you hold it.
- Normally closed (NC)
- A contact that conducts until operated. STOP is NC, so pressing it breaks the circuit. This is also fail-safe: a broken STOP wire stops the motor rather than leaving it uncontrollable.
- Seal-in (latch)
- The contactor's own NO contact is wired in parallel with START. Once the coil is energised, that contact closes and keeps the coil powered after START is released.
- Overload protection
- The overload relay watches motor current. If it stays too high, its NC contact opens and stops the motor, and a manual reset is needed before it can restart.
Tools on this site are for guidance and learning. Results and examples must be checked by a qualified engineer against the applicable standards before any installation or design decision.
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