Operation Modes
4-2
Eaton BladeUPS 12 kVA Maintenance Bypass Cabinet Installation and Operation Manual P-164000130—Rev 1
www.eaton.com/powerquality
4.2
Understanding Maintenance Bypass Mode
An MBB is used to safely supply utility power to the critical load during periods of UPS maintenance or repairs.
The bypass source supplies the commercial AC power to the load directly.
When the MBB is first closed, the load is wrapped around the UPS while power is still supplied to the load by
the UPS through the UOB. When the MBB closes, the UPS is signaled to go to maintenance bypass mode.
The UPS is still powering the load, but it is in maintenance bypass mode. Then, the UOB and RIB are opened,
isolating the UPS from the Bypass power source. The UPS can be safely shut down and power removed from
the UPS without interrupting power to the critical load. Once isolated, the UPS can be serviced or replaced
safely.
The critical load is not protected while the UPS is in Maintenance Bypass mode.
Figure 4-2 shows the path of electrical power through an example MBC when operating in Maintenance
Bypass mode.
CRITICAL LOAD
PANEL BOARD B
FROM UPS
OUTPUT
SYSTEM
INPUT
PANEL BOARD A
CRITICAL LOAD
TO UPS
RECTIFIER INPUT
UOB
MBB
RIB
480V
SIB
208V
MAIN POWER FLOW IN UPS MODE
MAIN POWER FLOW IN MAINTENANCE BYPASS MODE
Figure 4-2. Path of Current in Maintenance Bypass Mode Example
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