TM 5-3895-374-24-1
Troubleshooting and Maintenance of Square D Motor Control Equipment
WARNING: There is a hazard of electric shock or burn whenever working on or around electrical equipment. Turn
off power supplying this equipment before working inside motor control centers
Motor Control Trouble-Remedy Table
-.-2 The following table lists troubles encountered with
motor control, their causes and remedies This table is of
a general nature and covers only the main causes of
trouble.
Misapplication of a device can be a cause of serious
trouble, however rather than list this cause repeatedly it
should be noted here that misapplication Is a major
cause of motor control trouble and should always be
questioned when a device is not functioning properly.
Actual physical damage or broken parts can usually be
found quickly and replaced. Damage due to water or
flood conditions requires special treatment. Contact your
local Square D office.
TROUBLE
CAUSE
REMEDY
Contact Chatter
1.
Poor contact in control circuit.
1. Replace the contact device or use holding circuit (Also
see interlock (3 wire control).
"Noisy Magnet")
2.
Low voltage.
2. Check coil terminal voltage and voltage dips.
1.
Abnormal inrush of current.
1. Check foregrounds, shorts, or excessive motor load
current, or use larger contactor.
2.
Rapid jogging.
2. Install larger device rated for jogging service.
3.
Insufficient tip pressure.
3. Replace contacts and springs, check contact
carrier for deformation or damage.
4.
Low voltage preventing magnet from
4. Check coil terminal voltage and voltage dips
Welding or Freezing
sealing.
during starting.
5.
Foreign matter preventing contacts from
5. Clean contacts with Freon Contacts, starters, and
closing.
control accessories used with very small current or
low voltage, should be cleaned with Freon.
6.
Short circuit or ground fault.
6 Remove fault and check to be sure fuse or breaker size
is correct.
1.
Filing or dressing.
1. Do not file silver tips Rough spots or discoloration will
not harm tips or impair their efficiency.
2.
Interrupting excessively high currents.
2. Install larger device or check for grounds, shorts, or
excessive motor currents.
3.
Excessive jogging.
3. Install larger device rated for jogging service.
4.
Weak tip pressure.
4. Replace contacts and springs, check contact carrier
Short Tip Life or
for deformation or damage entry of foreign matter into
Overheating of Tips
enclosure.
5.
Dirt or foreign matter on contact surface.5
Clean contacts with Freon Take steps to reduce
6.
Short circuits or ground fault.
6. Remove fault and check to be sure fuse or breaker size
is correct.
7.
Loose connection in power circuit.
7. Clear and tighten.
8.
Sustained overload.
8. Check for excessive motor load current or install larger
device
COILS
Open Circuit
1.
Mechanical damage.
1. Handle and store coils carefully.
1.
Over voltage or high ambient tempera-
1. Check coil terminal voltage which should not exceed
ture.
110% of coil rating.
2.
Incorrect coil.
2. Install correct coil.
3.
Shorted turns caused by mechanical
3. Replace coil.
damage or corrosion.
4.
Under voltage, failure of magnet to seal.
4. Check coil terminal voltage, which should be at
Overheated Coil
5.
Dirt or rust on pole faces.
5. Clean pole faces.
6.
Mechanical obstruction.
6. WITH POWER OFF check for free movement of contact
and armature assembly.
(Page 3-147)