5.7 Wiring parallel 91PS/93PS UPS systems
The outputs of multiple UPS systems can be connected in parallel. Up to 4 units
can be paralleled. The UPS static bypass power rating needs to be identical
among all the paralleled units. However, paralleled UPS cabinets can be housed
with different number of UPM power modules.
The outputs are paralleled to increase the load capacity of the power system and
for redundancy. The system is paralleled for (N+1) redundancy as long as there is
always one or more UPS online than required to support the load. The system is
paralleled for capacity if all UPSs in a system are required to support the load.
Communication between the UPSs is required for system metering and mode
control. The system level communication and control are accomplished using a
Controller Area Network (CAN). A pull-chain signal in each UPS, connected to
the other UPSs in parallel and tied to the bypass status relay in each UPS, is
used for a secondary communication path. This arrangement ensures bypass
control even if the CAN bus is lost.
WARNING
Do not connect units equipped with an internal Maintenance Bypass
Switch (MBS) or internal transformers in parallel.
5.7.1 Power wiring overview
See Section 4.4.3 UPS system power wiring preparations for the recommended
cable and external fuse sizes and installation practices.
Input feed
The input feed is defined as the power source connected to the UPS rectifier. The
feed to all UPS’s inputs must be derived from the same source.
Bypass feed
The bypass feed is defined as the power source connected to the UPS bypass.
The feed to all UPS’s bypass must be derived from the same source. The
shortest length of power wire from the source to the UPS must be a minimum of
95% of the length of the longest wire.
Output
The neutrals of all the UPSs must be connected. The shortest length of wire from
the source to the UPS must be a minimum of 95% of the length of the longest
wire. The measurement is with respect to where the UPS’s outputs are tied.
© Eaton Corporation plc 2020. All rights reserved. Revision: 006 Document ID: P-164000493 70 (126)
Eaton 91PS/93PS UPS 8–40 kW User’s and Installation Guide
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