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the load is automatically or manually transferred back to
the normal power source, again depending upon the
type of transfer equipment being used (Figure 1-1).
In automatic transfer switch equipment, the switch's
intelligence system initiates the transfer when normal
power fails or falls below a preset voltage. If the emer-
gency power source is a standby generator, the transfer
switch initiates generator starting and transfers to the
emergency power source when sufficient generator volt-
age is available. When normal power is restored, the
transfer switch automatically transfers back and initiates
engine shutdown. In the event the normal power source
fails and the emergency power source does not appear,
the automatic transfer switch remains connected to the
normal power source until the emergency power source
does appear. Conversely, if connected to the emer-
gency power source and the emergency power source
fails while the normal power source is still unavailable,
the automatic transfer switch remains connected to the
emergency power source.
Automatic transfer switches automatically perform the
transfer function, and include three basic elements:
(1) Main contacts to connect and disconnect the load
to and from the source of power.
(2) A mechanism to make the transfer of the main con-
tacts from source to source.
(3) Intelligence/supervisory circuits to constantly moni-
tor the condition of the power sources and thus pro-
vide the intelligence necessary for the switch and
related circuit operation.
1.2.1 DESIGN CONFIGURATION
The Cutler-Hammer transfer switch is a rugged, com-
pact design that used molded case switches to transfer
essential loads from one power source to another
(Figures 1-2 [300-600A] and 4-2 [30-200A]). Molded
case switches are interlocked to prevent both switching
devices from being closed at the same time.
Molded case switches and the associated transfer
mechanisms are mounted vertically to save space in the
assembly. The compact, vertical configuration uses a
positive, metallic transfer and interlocking system
between the molded case switches.
The Cutler-Hammer automatic transfer switch was
designed with easy installation and simplified mainte-
nance in mind. Two main panels compromise the auto-
matic transfer switch design:
Figure 1-2 Automatic Transfer Switch Equipment with
Solid Steel Shield in Place over Power Panel
• Power Panel
• Microprocessor-based Controller
Each panel is independently mounted with interconnect-
ing wiring terminated in connector plugs to permit indi-
vidual door or panel removal without disturbing critical
connections. Mounting the enclosure is simple using
top and bottom mounting flanges with elongated mount-
ing holes. These mounting holes, along with power
panel positioning bolts and pre-tapped inserts insure
proper power panel mounting after initial enclosure
installation or when switching from top to bottom entry
and vice versa. Refer to Section 4 for mounting and
modification details.
1.3 TRANSFER SWITCH CATALOG NUMBER
IDENTIFICATION
Transfer switch equipment catalog numbers provide a
significant amount of relevant information that pertains
to a particular piece of equipment. The Catalog Number
Identification Table (Table 1.1) provides the required
interpretation information. An example is offered to ini-
tially simplify the process.
I.B. ATS-AG03
Effective 7/00
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