6
I.B. 8926-1A
not be used for storage and should have
adequate lighting.
3. Since control centers are assembled at the
factory on smooth and level surfaces to assure
correct alignment of all parts, control centers
should be securely mounted on a level surface.
The foundation furnished by the purchaser must
be true and level, or the bottom frames must be
shimmed to support the entire base in a true
plane. It is recommended that leveled channel
sills under both the front and rear of the control
center be used to provide this level base. Drill an
tap the channel sills for mounting bolts in
accordance with the applicable floor plan
drawing and then either install the MCC level
with, or on top of, the finished floor. If sills are
grouted in concrete, the mounting bolts should
be screwed in place and remain until the
concrete has hardened.
4. For bottom entry, position the motor control
center so that the conduit stubs or floor
openings are located in the shaded areas shown
on the MCC floor plan drawings (refer to pages
31 to 32 for floor plan dimensions). The shaded
areas represent the open space available for
conduit entry through the bottom of each
section. A shaded area may be restricted if large
controllers or autotransformers are mounted in
the bottom of the sections. If optional bottom
plates are supplied, the plates may be removed
and drilled for conduit entry.
5. Install the MCC in its final position, progressively
leveling each section and bolting the frames
together if they are separated. If necessary,
secure the MCC to walls or other supporting
surfaces. Do not depend on wooden plugs
driven into holes in masonry, concrete, plaster,
or similar materials. See NEC 110-13.
6. If two or more shipping sections are to be joined
into an integral assembly or a shipping section is
to be joined to an existing section, refer to
paragraphs below before proceeding with the
installation.
7. Ground and bond the motor control center as
follows:
a) Motor control centers used as service
equipment for a grounded system or as an
incoming line section for a separately-
derived previously grounded system:
i) Run a grounding electrode conductor
(ground wire) having a size in
accordance with NEC 250-94 from the
grounding electrode to the MCC ground
bus or ground terminal provided. See
also NEC 250-91(a) and 92(b).
ii) If the system is grounded at any point
ahead of the MCC, the grounded
conductor must be run to the MCC in
accordance with NEC 250-23(b), and
connected to the ground bus terminal.
iii) Do not make any connections to ground
on the load side of any neutral
disconnecting line or any sensor used for
ground-fault protection. Do not connect
outgoing grounding conductors to the
neutral.
b) Motor control centers used as service
equipment for an ungrounded system or as
an incoming line section for a separately-
derived previously ungrounded system:
i) Run a grounding electrode conductor
(ground wire) having a size in
accordance with NEC 250-94 from the
grounding electrode to the MCC ground
bus terminal. See NEC 250-91(a) and
92(b).
c) Motor control centers not used as service
equipment nor as an incoming line section
for a separately-derived system, and used
on either a grounded or ungrounded system:
i) Ground the MCC ground bus by means
of equipment grounding conductors
having a size in accordance with NEC
250-95 or by bonding to the raceway
enclosing the main supply conductors in
accordance with NEC 250-91(b).
8. When all wiring and adjustments are complete,
close all unit and wireway doors.
9. In damp indoor locations, shield the MCC to
prevent moisture and water from entering and
accumulating.
10. Unless the motor control center has been
designed for unusual service conditions, it
should not be located where it will be exposed to
ambient temperatures above 40
°
C (104
°
F),
corrosive or explosive fumes, dust, vapors,
dripping or standing water, abnormal vibration,
shock or tilting.
JOINING COMPATIBLE SECTIONS
If two more shipping blocks are to be joined into an
integral assembly, or a section added to an existing
installation, splicing or horizontal bus, ground bus,
neutral bus and joining of the adjacent vertical
sections must be planned with the installation.
1. Remove the side sheets from adjacent vertical
sections to be joined. (These sheets will have
been removed from factory-assembled
sections.)
2. The horizontal bus splice plates and connection
hardware will be shipped with the MCC attached
to one end of shipping section. Refer to Figure
4. This method provides the most convenient
