When a motor overload or circuit breaker trips and /or blows fuses, certain procedures and tests should be carried out:

* lockout and tag out main circuit breaker;

* test insulation resistance of motor wires and windings by using megohm meter between T1, T2, & T3 leads and ground, then;

* test "T" leads to motor with ohmmeter for continuity and ohm-age of windings between A to B, B to C, A to C; each resistance should be within 1 or 2 ohms of each other; if the ohms readings are significantly different, or, if there is no continuity; go to the motor disconnect box, turn it off, perform the continuity and resistance test on the "T" leads, again; if the readings are good, the problem is in the wires from the motor controller to the disconnect switch;

* check the three wires by disconnecting all three wires from switch and twist together; go to controller and check for continuity between A to C, B to C, A to C; one or more wires will be open or grounded;

* correct solution is to pull all new wires in from controller to motor disconnect switch, whatever caused the problem may have damaged the other wires, also, replace all wires

* if problem is on motor side of disconnect switch, open motor connection box and disconnect motor;

* check motor for resistance to ground with megger, if reading is below 5mega ohms, motor is grounded and must be replaced;

* test motor windings for ohms between phases with ohmmeter A to B, B to C, A to C, readings should be within 1 or 2 ohms of each other; if readings indicate open or a significant ohm age difference, replace motor;

* if motor test readings are good, test the motor leads between the disconnect switch and the motor connection box for continuity and ground resistance, if readings are not good, replace wires;

* if all readings are OK, reconnect motor, remove lockout, and restore to service; the problem could have been mechanical in nature; an overload on motor caused by the chain, belt, bad bearings, faulty gearbox, or power glitch.
Motor Controller:

* check motor Full Load Current (FLC) at motor and check setting on controller overload (OL) device; most newer OL devices are adjustable between certain ranges, some older OL devices use heaters for a given amperage

* if circuit disconnecting means in controller is a circuit breaker, it should be sized correctly

* if the disconnecting means is a Motor Circuit Protector (MCP), the MCP must be correctly sized for the motor it is protecting and the MCP has a trip setting unit which has to be correctly set based on the Full Load Amperage of the motor; using a small screwdriver, push in on the screw head of the device and move to a multiple of thirteen of the FLC; example: a motor FLC of 10 amps would require that the MCP trip device be set to an instantaneous trip point of 130 amps
* fuses protecting the motor should be the dual element or current limiting type and based on the motor FLC