Section IV
Multiple UPS Configurations
006-0007068 UPS-1500-S-2S Guide
Rev E
39 of 60
09/10/20
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 are directly parallelable between multiple
modules. Internal devices prevent circulating power between multiple units. The droop
characteristic provides current sharing between parallel connected modules. 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 or three UPS units in the multiple-unit configuration, there are several
ways that the AC and/or DC INPUTS can be connected to sources of power:
• 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 is to ensure that the input voltage falls within the specified range of the AC
and/or DC INPUTS 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 circuit breaker disconnects the unit from the AC input bus should a UPS
experience a hardware fault on its input stage. This, in conjunction with “R” option UPS units,
allows for robust N+1 or N+M multi-unit systems.
3-Phase AC INPUT Source
When three UPS units are used (with their AC OUTPUTS connected either in parallel or in a
3-Phase configuration), each UPS unit’s AC INPUT can be connected to a different phase of a
3-Phase source. There are two different ways to do this:
• each UPS unit’s AC INPUT can be connected from a line (i.e., L1 or L2 or L3) of the AC source
to the neutral wire of the AC source (assuming it is present), or
• each UPS unit’s AC INPUT can be connected from one line of the AC source to another (i.e.,
L1 to L2, L2 to L3, or L3 to L1)
