Overview of Parallel System

MIB Mains input breaker/switch
BIB Bypass input breaker/switch
UIB Unit input breaker/switch
SSIB Static switch input breaker/switch
UOB Unit output breaker/switch
Ext. UOB External unit output breaker/switch
MBB Maintenance bypass breaker/switch
Ext. MBB External maintenance bypass breaker/switch
SIB System isolation breaker/switch
BB Battery breaker/switch
NOTE: Refer to Appendix: Switch/Breaker Details for the disconnecting device type.
NOTE: In parallel systems with an external maintenance bypass breaker Ext. MBB, the maintenance bypass breakers/switches MBB must be padlocked in the open (OFF) position.

UPSs for External Batteries

UPSs for Internal Batteries

The impedance of the bypass paths need to be controlled in a parallel UPS system. When operating in bypass mode, the parallel load sharing is determined by the total impedance of the bypass path comprising cables, switchgear, static bypass switch, and cable formation.

Risk of equipment damage
To ensure correct load sharing in bypass operation in a parallel system, the following recommendations apply:
  • The bypass cables must be the same length for all UPSs.
  • The output cables must be the same length for all UPSs.
  • The input cables must be the same length for all UPSs in a single mains system.
  • Cable formation recommendations must be followed.
  • The reactance of busbar layout in the bypass/input and output switchgear must be the same for all UPSs.
If the above recommendations are not followed the result can be uneven load sharing in bypass and overload of individual UPSs.
Failure to follow these instructions can result in equipment damage.
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