IB01602017E
For more information visit: www.eaton.com
Instructional Booklet
Effective: July 2010
Page
3
ATC-100 Contactor Based Transfer Switch
1.2 General Information
Transfer switches are used to protect critical electrical loads
against loss of power. The load’s Utility power source is backed
up by a Generator power source. A transfer switch is connected
to both the Utility and the Generator power sources and supplies
the load with power from one of the two sources. In the event
that power is lost from the Utility, the transfer switch transfers
the load to the Generator power source. This transfer is auto-
matic. Once Utility power is restored, the load is automatically
transferred back to the Utility power source (Figure 2).
Figure 2. Typical Load Transfer Switch Schematic (Contactor
Type).
In ATS equipment, the switch’s intelligence system initiates the
transfer when the Utility power fails or falls below a preset volt-
age. If the Generator power source is a standby generator, the
ATS initiates generator startup and transfers to the Generator
power source when sufficient generator voltage is available.
When the Utility power is restored, the ATS automatically trans-
fers back and initiates generator shutdown. In the event the Util-
ity power source fails and the Generator power source does not
appear, the ATS remains connected to the Utility power source
until the Generator power source does appear. Conversely, if con-
nected to the Generator power source and the Generator power
source fails while the Utility power source is still unavailable, the
ATS remains connected to the Generator power source.
ATSs automatically perform the transfer function and include
three basic elements:
1. A power contactor to connect and disconnect the load to and
from either power source.
2. Solenoids to make the transfer of the main contacts from
source to source.
3. Intelligence/supervisory circuits to constantly monitor the con-
dition of the power sources and thus provide the intelligence
necessary for the switch and related circuit operation.
1.2.1 Design Configuration
The Eaton contactor based ATS is a compact design that uses a
power contactor to transfer essential loads from one power
source to another (Figure 3
[
400 A
])
.
The ATS contains suitable mechanical and electrical interlock
switches to eliminate the possibility of connecting the utility ser-
vice to the generator output. In addition, a manual override lever is
provided for the transfer function.
Figure 3. Typical 400 A ATS.
The Eaton contactor based ATS was designed with easy installa-
tion and simplified maintenance in mind. Two main panels com-
prise the contactor based ATS design:
1. Power panel; and
2. Microprocessor-based logic panel.
Each panel is independently mounted with interconnecting wiring
terminated at the connector receptacles on the ATC-100 Control-
ler. Door or individual panel removal is achieved without disturb-
ing critical connections by removing the connectors from the
receptacles and cutting the wire ties that secure the wires to the
door.
Utility
Generator
Load
WARNING
DO NOT MANUALLY TRANSFER THE SWITCH WHILE UNDER LOAD.
