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3.3.9 Maintenance Bypass
Maintenance Bypass switchgear allows you to totally isolate the UPS from all power sources, while
you maintain power to the critical load.
Your installation may have a two-breaker or three-breaker maintenance bypass or none at all. The
main difference between a two-breaker and three-breaker maintenance bypass is the location of the
Bypass Input Breaker (BIB).
Another option that may be present at your site is an alternate power source (generator) and an auto-
matic transfer switch (ATS).
Note that to totally isolate the UPS system from all power sources, the Main Input switchgear and
battery circuit breakers must also be opened.
Figure 50 Load on maintenance bypass (two breakers)
!
CAUTION
Instructions for operating the Maintenance Bypass circuit breakers are on the Maintenance
Bypass cabinet. Make sure you understand the proper sequence before operating any circuit
breaker. Operating a Maintenance Bypass circuit breaker out of sequence could cut off power
to the critical load.
Critical
Load
AC Output
RIB
MBD
MBFB
BIB
OUTPUT
CB
Controls
Battery
Bypass CB
INPUT
CB
Static
Bypass
Switch
Static
Switch
Disconnects
TWO BREAKER MAINTENANCE BYPASS SWITCHBOARD
CONTROL POWER
UPS MODULE
MAIN INPUT
SWITCHGEAR
Rectifier/
Charger
Inverter
MBB
MIB