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3.5.5 Setting Up External Communication Devices
All external communication devices, including the modem, are optional equipment. Connections to
communication ports are made by wiring cables to terminal boards. Connection points are shown on
the Control Wiring Interconnect Diagram in the Installation Manual. Contact Liebert Global Services
for assistance when attaching an external device to your UPS system.
Any terminal that accepts the standard 7-bit ASCII codes and conforms to the data link requirements
can be used to interface with the Npower UPS. If a printer is used, the terminal must support it. The
UPS does not send or receive any printer control commands.
Data link requirements are:
• Asynchronous RS-232 communication
• Terminals may be configured as DTE or DCE
• Baud Rate:
Modem 1200 or 2400
Terminal 9600 only
•Data Bits: 8
•Stop Bits: 1
•Parity: None
• Handshaking: Not required
•Full Duplex
3.6 Modes Of Operation
This section illustrates the flow of power through circuit breakers, switches, and UPS components dur-
ing various modes of operation. The same modes of operation apply to all configurations of the Liebert
Npower UPS. Highlighted (thick) lines in the diagrams indicate power flow and power availability.
3.6.1 Load on Bypass
Load on bypass, with the UPS not available, is shown in the figure below. The UPS system could be in this
mode of operation during either initial startup or UPS system shutdown and isolation for maintenance.
Figure 112Load on bypass, UPS not available
3.6.2 OK to Transfer
The OK to Transfer status message will be displayed when the bypass line and UPS system output
power are both available, their voltage, frequency, and phase synchronization are matched within
specifications, and the Static Switch Disconnects are closed (ON). An alarm message may be dis-
played to indicate Load on Bypass. If no alarm is displayed, the operating status is Load On UPS.
When the OK to Transfer message is displayed, you can perform a manual transfer of the load from
the UPS system to bypass, or a manual retransfer of the load from bypass to the UPS system. See
3.3.6 - Manual Transfer for more information.
MIMIC DISPLAY
SYS. STATUS
BATTERY
INV.
LOAD
RECT.
SS
SERV
NORM