IB140024EN
For more information visit: www.eaton.com
Instruction Booklet
Effective: October 2014
Page
3
ATC-300/900 40-400A (480/600Vac)
3-Postion Contactor Based Transfer Switch
1.2 General Information
Transfer switches are used to protect critical electrical loads
against loss of power. The load’s Source 1 power source is
backed up by a Source 2 power source. A transfer switch is
connected to both the Source 1 and Source 2 power sources and
supplies the load with power from one of the two sources. In the
event that power is lost from Source 1, the transfer switch trans-
fers the load to the Source 2 power source. This transfer is auto-
matic. Once Source 1 power is restored, the load is
automatically transferred back to the Source 1 power source
(Figure 2).
Source 1
Source 2
Load
Figure 2. Typical Load Transfer Switch Schematic (Contactor
Type).
In ATS equipment, the switch’s intelligence system initiates the
transfer when the Source 1 power fails, falls below, or rises
above a preset voltage. If the Source 2 power source is a
standby generator, the ATS initiates generator startup and trans-
fers to the Source 2 power source when sufficient generator
voltage is available. When Source 1 power is restored, the ATS
automatically transfers back and initiates generator shutdown.
In the event the Source 1 power source fails and the Source 2
power source does not appear, the ATS remains connected to
the Source 1 power source until the Source 2 power source does
appear. Conversely, if connected to the Source 2 power source
and the Source 2 power source fails while the Source 1 power
source is still unavailable, the ATS remains connected to the
Source 2 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
condition of the power sources and thus provide the intelli-
gence 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
[
400A
])
.
LOGIC
PANEL
VOLTAGE SELECTION AND
TRANSFORMER PANEL
POWER PANEL
Figure 3. Typical Power Panel for a 400A Model.
The Eaton contactor based ATS was designed with easy installa-
tion and simplified maintenance in mind. Three main panels com-
prise the contactor based ATS design:
1. Power panel;
2. Voltage selection and transformer panel (if required); and
3. Microprocessor-based logic panel.
