Electrical & Automation · Free tool
PLC control demo: motor start/stop
The most common circuit in industry: a motor started and stopped by pushbuttons, held on by its own contact, and protected by an overload relay. Operate it and watch the logic work.
Ladder logic
Copper lines are carrying current. NC = normally closed, NO = normally open.
Conveyor
Belt speed 0%
STOPPEDControl panel
Press and hold, like a real pushbutton.
Motor stopped
The motor is stopped. Press and hold START to energise the contactor coil.
The theory
How the 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.
Automating a machine or process?
We install and maintain control systems and automation panels. Tell us what you are working on.