Parallel System and LBS System Installation
Liebert
®
APM
™
44
4.3
LBS System
4.3.1 Cabinet Installation
A dual bus system consists of two independent UPS systems, each containing one or more parallel
UPS modules, as shown in
. The dual bus system has high reliability and is suitable for
loads with multiple input terminals. For a single-input load, an optional static transfer switch can be
fitted to achieve the transfer between the two outputs of the dual bus system.
Figure 30 Typical dual bus system (with STS and LBS)
The dual bus system uses the LBS to keep the output of the two independent UPS systems (or parallel
systems) in synchronization. One system is designated as the master, the other is designated as the
slave. The operation modes of the parallel system comprise master and/or slave operation in normal
or bypass mode.
Place the UPS modules side by side and interconnect the UPS modules according to the following
instructions.
4.3.2 External Protective Device
3.2 - External Protective Devices
.
4.3.3 Power Cable
The power cable wiring is similar to that of the UPS module. Refer to
The bypass and rectifier input supplies must use the same neutral line input terminal. If the input
has a current leakage protective device, the current leakage protective device must be fitted upstream
of the neutral line input terminal.
4.3.4 Control Cable
For Liebert APM-to-Liebert APM dual bus system, connect the optional LBS cables between the two
UPS systems as shown in
. The J3 and J4 ports are provided on the front panel of
the bypass module, as shown in
.
NOTE
Use the shortest LBS cable that will be functional for the application and do not coil excess
cable. Separate the LBS cable from the power cables to prevent electrical inteferences.
Main Input
Bypass
UPS1A
UPS1B
UPS2A
UPS2B
LBS
STS
To Load
Main Input
Parallel
Control
Cable
Main Input
Main Input
Bypass
Parallel
Control
Cable
