Dead motor? Walk the power side in order

The control circuit tells the contactor to close — but the power side is where the motor actually gets its three phases. Read the disconnect, fuses, contactor, and overload in order, and a dead motor gives up its cause fast.

A faultline101 training module · the skill behind six hands-on scenarios

The control circuit tells the contactor to close — the power side is where the motor gets its three phases. Read disconnect, fuses, contactor, and overload in order and a dead motor gives up its cause fast.

The idea

The power side of a motor circuit is a short, ordered chain: the disconnect, the branch protection (fuses or breaker), the contactor's power poles, the overload heaters, and the motor's three phases. When a motor won't run, you walk that chain in order — each link either passes power or it doesn't.

Read it against the one-line and the power schematic. A single missing phase (a blown fuse or a bad pole) doesn't stop the motor cleanly — it makes it hum, overheat, and draw hard: single-phasing. A tripped overload opens the control, not the power, but it's telling you the motor drew too much for too long. The print shows how these pieces connect the control decision to the actual three-phase power.

The most important split on the power side is power-versus-control. The contactor coil lives in the control circuit; its power poles live here. If the coil never pulls in, the motor is dead for a control reason, not a power one. Knowing which side you're on keeps you from megging a healthy motor when the real fault is a control permissive.

Six faults you'll work in this module

You don't learn this by reading it — you learn it by doing it on six different faults, each drilling the same skill until it's instinct:

1. Walk the power chain. The ordered chain localized it to the contactor.
2. It hums but won't turn. Read all three phases — one was gone: single-phasing.
3. The overload did its job. The overload protected the motor from a real overload.
4. Coil here, poles there. Ruling out both electrical sides pointed at the motor/load.
5. Power or control?. The power-vs-control split saved you from megging a good motor.
6. Cold: dead motor, find it. Ordered method, exact power-side fault.

The mistakes it kills

• Condemning the motor before checking the disconnect, fuses, contactor poles, and overload
• Missing single-phasing — one lost phase makes a motor hum and overheat, not stop cleanly
• Chasing the power side when the contactor never pulled in for a control reason

Why it matters: Reading the power side in order — disconnect, protection, contactor, overload, motor — turns a dead motor into a quick, specific find instead of a condemned motor and a wasted afternoon.

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