Section IV
Multiple UPS Configurations
006-0007129 10/12/2018
Rev B
41 of 60
UPS-1500 3-Phase Guide
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Parallel Connection of DC OUTPUTS
The DC1 OUTPUTS are not parallelable between multiple modules. A direct parallel connection
of DC1 OUTPUTS from different modules will result in a circulating power between the two UPS
devices. Diode-ORing devices added externally at the DC1 OUTPUTS will prevent any circulating
power. However, the outputs will still not necessarily share the load current equally.
DC2 OUTPUTS with the optional droop share feature can be directly paralleled for droop current
share applications. Internal devices prevent circulating power between multiple units. Care
should be taken to equalize the resistive drops between each unit and the load to maintain close
matching of output current between multiple devices.
Connection of the AC and/or DC INPUTS
Whether there are two, three or more UPS units in the multiple-unit configuration, there are
several ways that the AC and/or DC INPUTS can be connected to the input power sources:
• They could be connected to the same AC and/or DC source, respectively.
• They could be connected to different AC and/or DC sources, respectively.
All that is necessary for source input sharing is to ensure that the input voltage falls within the
specified range of the AC and/or DC INPUT specifications of the individual UPS units.
Furthermore, the individual AC and/or DC INPUT cables can be first combined into a single cable
(of appropriate minimum wire size), or they can be left as separate cables, each connected to
the desired AC or DC source.
Note that the UPS INPUT fuses disconnect the unit from the AC INPUT bus should a UPS
experience a hardware fault on its input stage. This feature, in conjunction with “R” expanded
redundant option, allows for robust N+1 or N+M multi-unit fault tolerant systems.
Multi-unit AC OUTPUT “ON/OFF” Control – Standard Parallel (“F” option)
In multi-unit operation, all combined front panel “ON” switches must be actuated before any
AC OUTPUT turns “ON”. Any “OFF” front panel switch actuation will cause all AC outputs to turn
“OFF”. In addition, the “REMOTE-ON” or “REMOTE-OFF” rear panel input signal may be utilized
for coordinated “ON/OFF” AC OUTPUT control. If any single UPS no longer has a valid input
power source (e.g., no AC or DC INPUT and a depleted battery), the combined AC OUTPUT of
the entire will shut down.
