Model 6 Motor Control Centers 80459-641-01E
Section 6—Maintaining the MCC 10/2012
© 1999–2012 Schneider Electric All Rights Reserved68
ENGLISH
4. Examine bus bars and incoming line compartments; tighten all electrical
connections to their proper torques. (Table 7 and Figure 96 show typical
bus connection points and torque values.) Replace any deformed bus
bars or connectors, as well as any showing signs of arcing damage.
Inspect all insulators for cracks or burn marks; replace any displaying
these characteristics.
5. Follow maintenance procedures for control units. Begin with
“Maintaining the Control Unit” beginning on page 56, and continue to
“Insulation Test” beginning on page 66. Also perform the steps listed
below:
a. Examine the disconnect means for evidence of possible damage.
Ensure that the operator mechanism properly turns the disconnect
on and off. Exercise the push-to-trip feature on circuit breakers.
Make sure that the operator mechanism properly resets the circuit
breaker.
b. Check that the door interlock keeps the unit door from opening while
the disconnect is in the on position.
NOTE: If the unit door must be opened while the unit is energized, only
authorized personnel may operate an interlock defeat mechanism (see
Figure 97).
c. Inspect the motor starters for damage. Replace contacts and contact
springs if the contacts are welded or show heat damage. If
deterioration extends beyond the contacts, replace the entire
contactor or starter.
d. Replace the complete overload relay if the thermal units are burned
out, or if any indications of arcing or burning are present on the relay.
e. Inspect all fuses and fuse clips. Replace all fuses in a set, even if
only one or two are open-circuited.
f. Check all conductors and other devices within the units for signs of
damage.
6. Complete an insulation test (see “Insulation Test” beginning on page 66)
before placing the MCC back into service.
7. Complete the “Pre-operation Checklist” beginning on page 53.
8. Re-energize the equipment. See“Energizing the MCC” beginning on
page 54.
Table 7: Bus Connection Torque Values
Bolted Connection
Location
Torque Range
Horizontal bus (all locations) 68–70 lb-ft (92.29–94.54 N•m)
Splice bars—0.375 in.
diameter bolts
31–32 lb-ft (41.64–43.33 N•m)
Horizontal ground bus (all
locations)
5–6 lb-ft (6.75–8.44 N•m)
Figure 96: Typical Bus Connection Points
AØ
AØ
BØ
CØ
AØ
BØ
CØ
BØ CØ
Typical Top-Located 600 A or 800 A Main Lug Compartment
Typical Splice Bar Connection Typical Horizontal Bus Connection
Splice bar
Figure 97: Operating Door Interlock Defeat
Mechanism
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