20
I.B. 8926-1A
16. Conduct an electrical insulation resistance test to
make sure that the MCC and field wiring are free
from short circuits and grounds. Do this test
phase-to-phase, phase-to-ground, and phase-to-
neutral, with the switches or circuit breakers
opened.
17. If the MCC contains a labyrinth vertical bus
barrier system, verify the operation of the
automatic shutters. See Part 9 for adjustments
of this mechanism.
18. Install covers, close doors, and make certain that
no wires are pinched and that all enclosure parts
are properly aligned and tightened.
19. Turn all circuit breakers and fusible switches to
the OFF position before energizing the bus.
Part 9
UNIT INSTALLATION AND ADJUSTMENT
DOOR REMOVAL AND INSTALLATION
All doors on the control center are mounted on pin
hinges to facilitate removal for installation and
maintenance operations. With the operating handle
on the OFF position, rotate the quarter-turn latches,
open the door, remove the hinge pins as shown in
Figure 26, partially close the door and lift it from the
structure. Reverse this procedure for installation.
UNIT REMOVAL AND INSTALLATION
After opening and/or removing the unit door, the
control unit is exposed. With a screwdriver, push in
on the latch at the top center of the unit and rotate ¼
turn counterclockwise.
CAUTION:
Units 18” or more
high have a retaining brace at the lower edge of
each side of the unit frame to add stability in
shipping. The shipping braces may be retained or
removed after installation; unscrew prior to unit
withdrawal. Pull-apart terminal blocks in the vertical
wireway must be disengaged (see Figure 27 and
page 10) and wiring from the unit to other units, to
master terminal blocks or to load devices must be
disconnected before the unit is removed. Grasp the
unit as shown in Figure 28 and pull it outward. The
first inch of travel pulls the stabs free from the
vertical bus, and the grounding clip on the side of
the unit frame is also disengaged.
To replace a control unit, position the mounting
points on the unit frame with the mating guide rails.
Slide the unit inward until all four mounting points
are engaged, then move it inward with a quick push.
This movement easily overcomes the compression
of the stabs as they engage the vertical bus. With
the unit in its correct position, the quarter-turn latch
is easily engaged by pushing inward and rotating ¼
turn clockwise.
Fig.26 Hinge Pin Removal
Fig. 27 Disengaging Pull-Apart Terminal Blocks
Fig. 28 Withdrawing a Unit
