IB140012EN
For more information visit: www.eaton.com
Instructional Booklet
Effective: March 2021
Page
37
Operation and Maintenance Manual,
Automatic Transfer Switch Controller, ATC-900
Feature 32D: In-Phase/Time Delay Neutral (3 Position)
In-phase transition is a feature that will allow a transfer between
two live sources only when the phase difference between the two
sources is near zero. This is an open transition transfer that pre-
vents in-rush currents from exceeding normal starting currents in
the case where motor loads are being transferred.
Time Delay Neutral provides a time delay in the transfer switch
Neutral position when both breakers/contactors are open. This
delay takes place when the load is transferred in either direction
to prevent excessive in-rush currents due to out-of-phase switch-
ing of large motor loads. This feature is not available with the
Neutral Load Sense Delay feature.
Feature 32F: In-Phase Transition
Provides In-Phase transition, which is a feature that will permit a
transfer or re-transfer between two available sources that have a
phase angle difference of five degrees or less with the number of
generators set to 1 or 2. The In-Phase transition feature includes
permissible frequency difference and synchronization time set-
points. In the event Source 1 and Source 2 fail to synchronize
within the permitted frequency difference and time, the alarm
relay will energize and “Failed to Sync” will be displayed on Line
1. After resetting the alarm, another in-phase transition may be
attempted or a non-synchronized transfer may be initiated by fail-
ing the connected source. The adjustable frequency difference is
0.0 to 3.0 Hz. If the synchronization does not occur within a
specified amount of time, the alarm relay will energize and the
failure will be logged into the Transfer History as either “Sync Fail
- Freq” or “Sync Fail - Phase” depending on whether the fre-
quency difference or the phase difference was excessive.
Feature 35A: Pre-Transfer Signal
Typically associated with elevator controls, this feature provides a
form C output to remotely signal an elevator that a re-transfer is
about to take place. If there is a power outage, the Pre-Transfer
(TPRE) is skipped. The ATC-900 has a programmed pre-transfer
delay timer that can be set from 0 to 120 seconds. Timers, such
as TDNE, will time out before the PRE-Transfer signal occurs.
Feature 35D: Post-Transfer Signal
This feature provides a form C output from the ATC-900 to signal
that the switch did transfer. It can be set for 0 to 120 seconds.
The Post Transfer output is enabled during neutral (Time Delay
Neutral) but it does not start to count down TDPOST until con-
nected to the new source.
Feature 35C: Pre/Post Transfer
This feature provides a form C output from the ATC-900 to signal
that a re-transfer is about to take place. It also energizes the out-
put to signal that the switch did transfer. The Pre/Post signal will
remain enabled from the time Pre-Transfer starts until the Post-
Transfer finishes, inclusive of any TDN.
Feature 36A: Emergency Inhibit (Load Shed)
This feature enables the Emergency Inhibit control input to inhibit
transfers to the Non-preferred (Emergency) Source. See the Con-
trol Inputs section for more information. The ATC-900, when
used in conjunction with the optional DCT metering module, has
the ability to shed and pick up loads based on available generator
capacity. Depending on the number of loads to be managed, an
accessory I/O module may be required.
Feature 37: Go to Isolated (Neutral) Position
The Go to Isolation Position feature will allow the user to close
contacts and force the switch to an open or tripped (isolated)
mode. The controller's screen will display “Go to Neutral” when it
is activated.
Feature 37A: Service Equipment
This factory programmed feature makes the transfer switch suit-
able for a service equipment rating by responding to a Go-To-Neu-
tral input. This will also put the controller into Monitor Mode. This
feature is not available on contactor switches as Service Equip-
ment but is available as a Go To Neutral input.
Feature 45A-L: Load Sequencing Capability
This feature provides the sequential closure of up to ten remote
relays after a transfer. A customer programmed time delay is
available to delay closure between each of the relays. Usually an
I/O module will be used for this but the controller can be used
depending on the amount of I/Os required.
Feature 46: Potential Transformer (PT) Ratio
This feature allows external voltage transformers to be used on
the ATC-900’s source and load sense inputs. Once this option is
enabled, the PT Ratio setpoint can be adjusted in steps of 1,
between 2:1 and 500:1. Also, when this option is enabled, the
Nominal System Voltage setting will be fixed at 120 or 110 volts,
depending upon the Nominal System Frequency setting. If the
Nominal System Frequency setting is 60 Hz then the Nominal
System Voltage will be fixed at 120 volts and all voltage pick-up
and drop-out setpoints will be based upon the 120 volt level. The
same is true of a Nominal System Frequency of 50 Hz whose
Nominal System Voltage will be fixed at 110 volts. The metering
display will use the PT Ratio value to calculate and display the
load and source voltages.
Feature 47x: Closed Transitions
See section 1.5.3 Closed Transition Type Operation
Feature 48F: Modbus RTU (RS-485)
This option provides integrated communications for the ATC-900
via Modbus RTU through an RS-485 port. Registers are available
to read back status, voltages, frequencies, and historical data.
Registers are also available for transfer switch control. Setpoints
may be read back and/or programmed via a pass-through com-
mand. History and Events may also be read. Consult the ATC-900
Modbus Communications Guide (IB140006EN) for a full list of
Modbus registers on the Eaton.com website. A "disabled" option
has been added to the Modbus Configuration setpoint for an
increased level of security in installations where Modbus commu-
nications are not desired.
ATC-900 Primary/Secondary Implementation
Feature 90A and 90B: Primary Secondary (Three Source ATS
Control)
The ATC-900 Primary/Secondary controller functionality provides
the user with the ability to control a three source system consist-
ing of a utility and two generator sources. In a three source sys-
tem, the Primary ATS controls the engine starting and stopping of
the Secondary ATS. See Figure 19 for a block diagram of the high
level connections. The Secondary ATS is kept powered up from
24VDC from the generator battery using the DCT module or a
120VAC UPS.
