Motor circuit troubleshooting trainer
A three-wire starter with a hidden fault and a voltmeter: place your leads, work the panel, and name the fault.
The complaint
6:40 AM: "The compressor's just dead. Press start — nothing. No click, no hum. It ran fine last night."
Result
Voltmeter · AC
Click a test point for the red lead, another for the black. After both are set, new clicks walk the red lead; click a lead to lift it.
No calls yet — measure first, then name it below the diagram.
Call it — what is the fault?
How it works
Using the tool
A three-wire starter with a hidden fault, and the tool every electrician actually reaches for: a voltmeter. The diagram shows what your eyes can see — buttons, the contactor, the motor. Voltage is invisible. Click two test points to set your leads, work the panel while you measure, and name the fault.
The method
The method is half-splitting a series loop: in a dead control circuit, the full 120 V appears exactly across the one element that's open — everything closed reads 0. Walk the red lead point to point and the fault names itself. Two habits make it work: hold START while you measure (a loop open in two places leaves the middle floating, and floating points read a useless 0), and remember that an intact coil with no current flowing drops nothing — hot rides through it to the far side.
On the power side the move is the fuse check: 0 V across a good fuse, full line voltage across a blown one — but only when the contactor gives the meter a path. And two diagnoses don't need a meter at all: hold-to-run is the seal-in, and a growl on pull-in is a missing phase. Symptoms first, meter second, hands last.
New to the math? Learn the concept: Motor circuits