Motor control, one rung at a time
Twelve short lessons that take you from "what is a ladder diagram" to finding a burnt-out coil with a meter. Every lesson has a live circuit you operate yourself: hold the buttons down, trip the overload, time the timers, kill the power. Each lab gives you a few things to do and ticks them off as you do them, with what just happened explained the moment it happens.
Do them in order the first time — each one uses the one before. Your progress stays in this browser.
- Reading a ladder diagramRails, rungs, NO and NC, coils and the contacts they move.
- Two-wire vs three-wire controlA float switch versus Start/Stop — and what happens when the power blinks.
- Start/stop and the seal-inThe holding contact, pilot lights, and your first meter readings.
- The overload relayWhere it senses, what it opens, and why reset does not restart.
- More than one stationStops in series, Starts in parallel.
- Jogging (inching)Run/Jog selector, and the safer jog with a control relay.
- Forward / reverseInterlocks, and what happens without them.
- On-delay and off-delay timersTimed contacts: a warning horn and a fan run-on.
- Sequence controlPermissives: one motor must run before the next.
- Hand-Off-AutoA selector that hands control to a float switch.
- Wye-delta startingA timer, three contactors and two interlocks.
- Troubleshooting a control circuitHidden faults, a meter, and the method that finds them.
Power circuit and control circuit
Every motor starter has two circuits in it. The power circuit carries the motor current: supply, disconnect, fuses or breaker, the starter's main contacts, the overload relay's sensing elements, the motor. The control circuit decides when the main contacts close: pushbuttons, switches, relay and timer contacts, and the starter's coil. It usually runs at a lower voltage from a small control transformer, which is why its rails are marked X1 and X2.
These lessons are about the control circuit — the ladder diagram — because that is where the logic lives and where most of the troubleshooting happens. The labs show the motor as a simple fan that spins, reverses or starts slow.
Before you start
- If series and parallel still feel shaky, do the series / parallel practice first. A rung is just series and parallel contacts.
- The electrical symbols page has every mark these diagrams use.
- The how to read a schematic lesson covers tracing a circuit in general.
Nothing here tells you how to size, rate or install anything. Starter sizes, overload settings, conductor sizes and control transformer protection come from the motor nameplate, the manufacturer and your code book. These labs teach how the logic behaves.
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