Hach sc200 - Table 17: Motor Control Center Troubleshooting Chart

80459-641-01E Model 6 Motor Control Centers
10/2012 Section 11—Troubleshooting
© 1999–2012 Schneider Electric All Rights Reserved
101
ENGLISH
Table 17: Motor Control Center Troubleshooting Chart
Part Problem Cause Remedy
Contacts
Contact Chatter (also
see Noisy Magnet)
1. Poor contact in the control circuit.
1. Replace the contact device or use a holding circuit interlock
(3-wire control).
2. Low voltage. 2. Check the coil terminal voltage and voltage dips during starting.
Welding or Freezing
1. Abnormal inrush of current.
1. Check for grounds, shorts, or excessive motor load current, or
use larger contactor.
2. Rapid jogging. 2. Install a 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 which prevents the magnet
from sealing.
4. Check the coil terminal voltage and voltage dips during starting.
5. Foreign matter prevents the contacts
from closing.
5. Clean the contacts with an environmentally safe (CFC-free)
contact cleaner.
6. Short circuit or ground fault.
6. Remove the fault. Ensure that the fuse and circuit breaker sizes
are correct.
Short Trip Life or
Overheating or Trips
1. Filing or dressing.
1. Do not file the silver tips; rough spots or discoloration do not
harm tips or impair their efficiency.
2. Interrupting excessively high currents.
2. Install a larger device or check for grounds, shorts, or excessive
motor currents.
3. Excessive jogging. 3. Install a larger device rated for jogging service.
4. Weak tip pressure.
4. Replace contacts and springs; check the contact carrier for
deformation or damage.
5. Dirt or foreign matter on the contact
surface.
5. Clean contacts with an environmentally safe (CFC-free) contact
cleaner. Reduce the entry of foreign matter into the enclosure.
6. Short circuit or ground fault.
6. Remove the fault; ensure that the fuse and circuit breaker sizes
are correct.
7. Loose connection in the power circuit. 7. Clear and tighten the connection.
8. Sustained overload.
8. Check for excessive motor load current or install a larger
device.
Coils
Open Circuit Mechanical damage. Replace the coil; handle and store replacement coils carefully.
Overheated Coil
1. Overvoltage or high ambient
temperature.
1. Check the coil terminal voltage. It should not exceed 110% of
the coil rating.
2. Incorrect coil. 2. Install the correct coil.
3. Shorted turns caused by mechanical
damage or corrosion.
3. Replace the coil.
4. Undervoltage; failure of the magnet to
seal in.
4. Check the coil terminal voltage. It should be at least 85% of the
coil rating.
5. Dirt or rust on the pole faces. 5. Clean the pole faces.
6. Mechanical obstruction.
6. With power off, check for free movement of the contact and
armature assembly.
Thermal Overload
Relays
Tripping
1. Sustained overload.
1. Check for excessive motor currents or current unbalance;
correct cause.
2. Loose or corroded connection in the
power circuit.
2. Clean and tighten the connection.
3. Incorrect thermal units.
3. Replace the thermal units with the correct size for the
application.
4. Excessive coil voltage. 4. Voltage should not exceed 110% of the coil rating.
Failure To Trip
1. Incorrect thermal units.
1. Check the thermal unit selection table. Install the proper thermal
units.
2. Mechanical binding, dirt, corrosion, etc. 2. Replace the relay and thermal units.
3. Relay previously damaged by a short
circuit.
3. Replace the relay and thermal units.
4. Relay contact welded or not in series with
the contactor coil.
4. Check circuit for a fault and correct the condition. Replace the
contact or the entire relay as necessary.