40 Chapter 4 Operations
6. In the assumption that 95sqmm AC cable is used, current sharing inductors (optional) are needed whenever one of
the following conditions is not satisfied:
• Max power per UPS rack Unit: 120kW
• The paralleling cables are connected to circuit breakers/fuses of the same rating and type
• Being L
max
and L
min
the maximum and minimum length of the connecting cables, measured from the
input distribution breaker upstream the UPS to the downstream distribution breaker upstream the load
o for 2+0 APM in Parallel connected:
L
min
> 5.5 m ; L
max
< 2* L
min
- 5.5 m
o for 3+0 APM in Parallel
L
min
> 8 m ; L
max
< 1.64* L
min
- 5.1 m
o for 4+0 APM in Parallel
L
min
>
10 m
; L
max
<
1.5*
L
min
-
5 m
Note: if the max number of future parallel unit is unknown it is suggested to follow the rule
L
min
>
10 m
; L
max
<
1.5*
L
min
-
5 m
Note
solation transformers are requested for applications where sources do not share the same neutral reference or where the neutral
is not available.
5.3 Operating Mode
The LIEBERT APM UPS is an on-line, double-conversion, reverse-transfer UPS that permits operation in these
modes:
Normal mode
Battery Mode
Auto-restart mode
Bypass mode
Black start mode
Maintenance mode (manual bypass)
Parallel redundancy mode
Sleep Mode
5.3.1 Normal Mode
The UPS inverter power modules continuously supplies the critical AC load. The rectifier/charger derives power from
the AC mains input source and supplies DC power to the inverter while simultaneously FLOAT or BOOST charging its
associated backup battery.
5.3.2 Battery Mode
Upon failure of the AC mains input power; the inverter power modules, which obtains power from the battery, supplies
the critical AC load. There is no interruption in power to the critical load upon failure. After restoration of the AC mains
input power, the “Normal Mode” operation will continue automatically without the necessity of user intervention.