Three-Phase DOL Motor Starter
How an industrial motor is started: three live phases, each on its own Type-D breaker, into a three-pole contactor and out to the windings. Direct-on-line means the motor gets full voltage from the first turn.
Components Needed
Text Wiring Path
L1 → MCB D → Contactor → Motor U L2 → MCB D → Contactor → Motor V L3 → MCB D → Contactor → Motor W Earth → Motor frame (PE)
Schematic
Steps
- 1Place three Live terminals (L1, L2, L3) and an Earth terminal down the left of the canvas.
- 2Give each phase its own Type-D MCB — the D curve rides out the motor's starting surge.
- 3Place a three-pole contactor after the breakers, then a 3-phase motor as the load.
- 4Wire L1, L2 and L3 through their breakers into contactor poles 1, 2 and 3.
- 5Take the three switched phases out to the motor's U, V and W terminals.
- 6Run Earth to the motor frame, press Run, then open any one breaker — losing a single phase stops the motor.
A three-phase motor needs no neutral: the windings are each other’s return path. What it does need is per-phase overcurrent protection, a contactor that breaks all three poles together, and a protective earth on the frame.
Three-phase work is not a step up from domestic wiring — 400 V between phases, and a motor that can start unexpectedly if its control circuit is energised. Isolate and lock off all three phases, prove dead, and check rotation before coupling a load.
Terms used here
Defined in the glossary — each one opens at its own entry.
Now wire it for real.
Build this circuit in the browser, inject a fault, and watch the protection respond.