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IB01602007E
Instruction Bulletin
Page
10
Effective: June 2003
O&M Manual for
Non-Automatic Transfer
Switches (30 – 1200 Amperes)
3.2.1 Vertical Design Steel Base Plate
The steel base plate on the vertical design permits the
power panel to be moved vertically within the enclosure
to accommodate top or bottom cable entry (Figure 13).
Elongated holes on either side of the base plate ensure
proper positioning. The bottom set of elongated holes posi-
tion the power panel higher in the enclosure, thus permitting
bottom cable entry. The top set of elongated holes position
the power panel lower in the enclosure for top cable entry.
Section 4 discusses equipment mounting and load lug
location in detail.
3.2.2 Main Contacts
The main contacts connect and disconnect the load to
and from the different power sources. High withstand
molded case switches are the main contacts for the Normal
and Emergency power sources in standard, unmodified
automatic transfer switches. Optional integral thermal and
short circuit protection in either or both switching devices is,
however, available (Figure 8 and Section 3.5). These contin-
uous duty switches are rated for all classes of loads, open
or enclosed. In addition, they have high dielectric strength,
heavy-duty switching and withstand capabilities, and high
interrupting capacity. The switches incorporate positive,
quick-make, quick-break toggle mechanisms and DE-ION
T
arc chutes.
Vertically mounted switching devices are mechanically
and electrically interlocked to prevent the two sets of main
contacts from being closed simultaneously. The load side
contacts of each switching device are joined with a bus bar
assembly to form a common load terminal location, either
top or bottom (Figure 14).
Horizontally mounted switching devices are also mechani-
cally and electrically interlocked. The molded case switches
are kept trip-free in the closed position. This permits thermal
and short circuit protection to be incorporated in either or
both interrupters.
3.2.3 Vertical Design Transfer Mechanism
The transfer mechanism transfers between power sources
through a motor driven ratchet type operation. A rotational
motion is created on an indicator wheel by the ratchet’s
operation. The indicator wheel is attached to rigid shafts
which covert the rotary motion into vertical linear motion.
Opening and closing of the switching devices is accom-
plished as a result of this vertical linear motion. The transfer
mechanism is mounted in front of the molded case switches
(Figure 6).
A solid steel shield attached to the ratchet assembly permits
viewing of the rotary switch position indicator while restrict-
ing access to other parts of the power panel (Figure 3).
3.2.4 Horizontal Design Transfer Mechanism
The horizontal design mechanism consists of a pivoting
rocker-arm lever which operates the switch handles as the
arm is moved by a rotating lever connected to the transfer
motor. A slide pin engaging a pivot in the rotating lever con-
verts rotary motion to linear motion. Motor limit switches
are mounted externally to the molded case switches and
operated by the rotating lever. Each limit switch is synchro-
nized with its associated molded case switch to operate
when its switch closes (Figure 7).
Figure 8. Molded Case Switches Mounted in Vertical Design
(Transfer Mechanism Removed for Clarity)
