|
Troubleshooting Guide For
Three-Phase Motors |
| Problem |
Possible
Cause |
Suggested
Test Tool |
Corrective
Action |
|
|
Motor will not start
 |
Wrong motor connections |
|
Most three-phase motors are dual-voltage. Check
for proper motor connections. |
| Blown fuse or
open CB |
Basic electrical
tester, DMM,
clamp meter,
megohmmeter |
Test the OCPD. If voltage is
present at the input, but not the output of the
OCPD, the fuse is blown or the CB is open. Check
the rating of the OCPD. It should be at least
125 % of the motor's FLC. |
|
Motor overload on starter tripped |
|
Allow overloads to cool. Reset overloads. If
reset overloads do not start the motor, test the
starter. |
| Low or no
voltage applied to motor |
Basic electrical
tester, DMM,
clamp meter |
Check the voltage at the motor terminals. The
voltage must be present and within 10 % of the
motor nameplate voltage. If voltage is present
at the motor but the motor is not operating,
remove the motor from the load the motor is
driving. Reapply power to the motor. If the
motor runs, the problem is with the load. If the
motor does not run, the problem is with the
motor. Replace or service the motor. |
|
Open control circuit between incoming power and
motor |
Basic electrical tester, DMM,
clamp meter |
Check for cleanliness, tightness, and breaks.
Test the circuit starting with the incoming
power and moving to the motor terminals. Voltage
generally stops at the problem area. |
|
Fuse, CB, or overloads
retrip after service
 |
Power not
applied to all three lines |
Basic electrical
tester, DMM,
clamp meter |
Measure voltage
at each power line. Correct any power supply
problems. |
|
Blown fuse or open CB |
Basic electrical tester, DMM,
clamp meter,
megohmmeter |
Test
the OCPD. If voltage is present at the input,
but not the output of the OCPD, the fuse is
blown or the CB is open. Check the rating of the
OCPD. It should be at least 125 % of the motor's
FLC. |
| Motor overload
on starter tripped |
|
Allow overloads
to cool. Reset overloads. If reset overloads do
not start the motor, test the starter. |
|
Low or no voltage applied to motor |
Basic electrical tester, DMM,
clamp meter |
Check the voltage at the motor terminals. The
voltage must be present and within 10 % of the
motor nameplate voltage. If voltage is present
at the motor but the motor is not operating,
remove the motor from the load the motor is
driving. Reapply power to the motor. If the
motor runs, the problem is with the load. If the
motor does not run, the problem is with the
motor. Replace or service the motor. |
| Open control
circuit between incoming power and motor |
Basic electrical
tester, DMM,
clamp meter |
Check for cleanliness, tightness, and breaks.
Test the circuit starting with the incoming
power and moving to the motor terminals. Voltage
generally stops at the problem area. |
|
Motor shaft does not turn |
|
Disconnect the motor from the load. If the motor
shaft still does not turn, the bearings are
frozen. Replace or service the motor. |
|
Motor
overheats
 |
Motor is single
phasing |
Basic electrical
tester, DMM,
clamp meter |
Check each of
the three-phase power lines for correct voltage. |
|
Improper ventilation |
Infrared temperature |
Clean all ventilation openings. Vacuum or blow
dirt out of motor with low-pressure, dry,
compressed air. |
| Motor is
overloaded |
Basic electrical
tester, DMM,
clamp meter,
DMM with clamp accessory |
Check the load for binding. Check shaft
straightness. Measure motor current under
operating conditions. If the current is above
the listed current rating, remove the motor.
Remeasure the current under no-load conditions.
If the current is excessive under load but not
when unloaded, check the load. If the motor
draws excessive current when disconnected,
replace or service the motor. |
| |
Excessive harmonics |
Power quality analyzer |
Check for the presence of harmonics in the
feeder supplying the motor, especially 5th
harmonic which can generate heat rise. |
