Table 1-1.-Troublesbooting Chart-Continued -141210033

Table 1-1.-Troubleshooting Chart-Continued

4. Place the voltmeter probes at C and F. A voltage

When starting a three-phase motor and the motor

reading with the start button closed would indicate a

fails to start and makes a loud hum, you should stop the

good OL1, but also would indicate an open OL3, an open

motor immediately by pushing the stop button. These

relay coil, or an open connection to line 3.

symptoms usually mean that one of the phases to the

motor is not energized. You can assume that the control

5. Place the voltmeter probes at points C and G

and close the start switch. A no-voltage reading indicates

circuit is good since the main operating coil has operated

the OL3 contacts are open.

and the maintaining contacts are holding the main

operating contactor in. Look for trouble in the power

A faulty holding relay contact will be indicated

circuit (the main contacts, overload relays, cable, and

when the system operates as long as the start switch is

held in, but stops when the start switch is released.

motor).

1-21