UNDERSTANDING MBM OPERATION
Eaton 9395 Maintenance Bypass Module Installation and Operation Manual
S
164201719 Rev 3
www.eaton.com/powerquality
5-3
5.4
Maintenance Bypass Mode Current Flow
An MBP 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 MBP is closed, the load is wrapped around the UPS while power is still
supplied to the load by the UPS through the MIS. The MIS is then 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. If the optional
BIB and RIB are installed, the BIB and RIB are opened to remove power from the
UPS. Otherwise, external upstream breakers are used to remove power. The UPS
now can be serviced or replaced safely.
The critical load is not protected while the UPS is in Maintenance Bypass mode.
Figure 5‐2 shows the path of electrical power through the MBM when operating in
Maintenance Bypass mode.
Output To Critical Load
MBM
MBP
AC Input to MBM
from Utility
Main Power Flow in UPS Mode
Main Power Flow in Maintenance Bypass Mode
RIB
(Optional)
BIB
(Optional)
MIS
To UPS Rectifier Input
From UPS Output
To UPS Bypass Input
Figure 5‐2. Path of Current Through the MBM in Maintenance Bypass Mode