Overview of Parallel System

MIB	Mains input breaker/switch
BIB	Bypass input breaker/switch
UIB	Unit input breaker/switchUnit input switch
SSIB	Static switch input breaker/switchStatic switch input switch
UOB	Unit output breaker/switchUnit output switch
Ext. UOB	External unit output breaker/switch
MBB	Maintenance bypass breaker/switchMaintenance bypass 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

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.

NOTICE
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.

NOTICE

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.