Initial Maintenance of the Control Units

The Model 6 MCC is designed for convenient and quick control unit removal and replacement. To remove control units:

1. Turn off all power supplying this equipment before working on or inside the equipment, and follow lockout/tagout procedures. Always use a properly rated voltage sensing device to confirm the power is off.

2. Move the operator mechanism to the OFF position (see Operator Mechanism in the OFF Position).

   Operator Mechanism in the OFF Position

   

3. Loosen the fasteners on the door and open it. Use a properly rated voltmeter to check for live circuits. Deenergize any voltage sources.

   NOTE: Arc-rated units have additional fasteners at the topmiddle and bottom-middle of the door that must be loosened to open the door.

4. Release the lock-in device located at the bottom front of the unit (when supplied) by turning the screw on the front of the device until the locking pawl is parallel to the bottom of the unit.

5. Disconnect the power wiring from the starter terminals or, if provided, the power terminal blocks. Tag the terminations for re-installation.

6. Remove the top portion of the pull-apart control terminal blocks to which field wiring is connected.

7. Push the power leads and the top portion of the control pull-apart terminal blocks through the wiring port and into the vertical wireway.

8. Pull forward on the twin handle cam mechanism located at the top front of the unit to rack the unit partially out of the structure (see Pulling the Twin Handle Cam Mechanism Forward). This action disconnects the power stabs from the vertical bus. Continue pulling forward until the handles are fully extended.

   Pulling the Twin Handle Cam Mechanism Forward

   

9. The operator mechanism-to-structure interlock prevents the control unit from being withdrawn or inserted with the handle in the ON position (see Operating the Mechanism-to-Structure Interlock).

   Operating the Mechanism-to-Structure Interlock

   

10. If the withdrawn unit is left in the structure, use appropriate lock-out procedures to avoid re-loading by non-authorized personnel (see Locked Out Unit).

    Locked Out Unit

    

11. Remove the control unit from the structure for servicing. In units with a full bottom plate, additional accessibility to the components and wiring can be achieved by folding the bottom plate down. To do so, lean the unit on its back, remove the two front screws, and fold the bottom plate down (see Control Unit with Bottom Plate Folded Down).

    NOTE: Some MCC units can weigh up to 200 lbs. (90 kg) and require two or more persons or special handling equipment. Lift only by supporting bottom and/or side panels of the unit.

    Control Unit with Bottom Plate Folded Down

    

12. If necessary, the unit door can be taken off its hinges without removing the unit. To do so, drive the hinge pins out of the hinge collars, using a small flat-bladed screwdriver or small punch. Remove the bottom hinge pin first.

13. When reinstalling a hinge pin, make certain that the hooked end is fully engaged into the hinge collar.

1. Turn off all power supplying this equipment before working on or inside the equipment, and follow lockout/tagout procedures. Always use a properly rated voltage sensing device to confirm power is off.

2. Move the operator handle to the OFF position.

3. Loosen the fasteners on the door and open it.

   NOTE: Arc-rated units have additional fasteners at the top-middle and bottom-middle of the door that must be loosened to open the door.

4. Check for live circuits using a properly rated voltage sensing device. Deenergize any voltage sources.

   NOTE: Removal of the control station plate may be necessary to perform steps 5 and 6. To remove the control station plate, follow these steps:

   1. Loosen the captive mounting screws holding the plate to the front of the unit.

   2. Remove the plate from the unit (see Operator Handle Flange).

   3. Re-attach the plate after disconnecting the load wires and control terminal block.

   NOTE: Do not disconnect the wires to the control station plate.

5. Disconnect the power wiring from the starter terminals. Tag the terminations for re-installation.

6. Remove the top portion of the pull-apart control terminal block to which field wiring is connected.

7. Push the power leads and the top portion of the control pull-apart terminal blocks through the wiring port and into the vertical wireway.

8. Grasp the operator handle flange and press down on the structure interlock release (see Operator Handle Flange).

   Operator Handle Flange

   

9. Firmly pull the unit forward to disengage the power stabs from the vertical bus. The unit should now slide freely from the MCC structure.

10. The operator mechanism-to-structure interlock prevents the control unit from being inserted or withdrawn with the handle in the ON position.

11. If the withdrawn unit is left in the structure, use appropriate lock-out procedures to avoid re-loading by non-authorized personnel (see Control Unit with Bottom Plate Folded Down).

12. Remove the control unit from the structure and place it on a flat surface for servicing.

Once the control unit is removed, perform the following tests and initial maintenance:

Circuit Breaker or Disconnect Switch: Verify proper operation of the circuit breaker or disconnect switch. Exercise the push-to-trip feature on the circuit breakers.

Operator Mechanism: Verify proper operation of the operator mechanism (see Operator Mechanism in the Tripped Position). Test for proper ON, TRIP, and OFF positions. Verify proper door interlock operation.

Operator Mechanism in the Tripped Position

Fuses: Inspect all fuses and fuse clips.

Control Devices: Check for proper operation of starters, relays, timers, and other control devices.

Overload Relay: Manually trip the overload relay to ensure proper operation. Verify that the thermal unit is the proper size for the application. Refer to the thermal unit selection tables in this instruction bulletin.

Wiring and Electrical Connections: Verify that all electrical connections are correct; tighten them if necessary. For any inaccessible electrical connections, please contact Schneider Electric Services. Also inspect all power and control wiring, replacing any wire that has damaged insulation.

Starter Interlocks: Check the mechanical interlocks on reversing, multispeed, or reduced voltage starters.

Special Units: Follow the manufacturer’s recommended maintenance procedures for special units (for example: drives, soft starts, and automatic transfer switches).

To reassemble the MCC after testing and maintenance:

1. Reinstall Compac 6 units by reversing removal steps 1–12 in Removing the Compac™ 6 Control Unit. Reinstall all other units by reversing removal steps 1–13 in Removing the Standard Control Unit.

2. Confirm the cam mechanism is in the open position; position the mounting slides of the control unit onto the slots of the mid-shelf. Slide the unit inward to engage the cam mechanism.

   For Compac 6 units, position the mounting slides of the control unit onto the slots of the mid-shelf. Slide the unit inward until the unit is halfway in, then move it inward with a quick push. This movement easily overcomes the compression of the stabs as they engage the vertical bus.

3. Replace all barriers and cover plates and close and fasten all doors.