UNDERSTANDING MBM OPERATION
Eaton 9395 Maintenance Bypass Module Installation and Operation Manual
S
164201719 Rev 3
www.eaton.com/powerquality
5-2
Key A is removed from the the solenoid lock, inserted in the MBP key A slot, and the
MBP closed. This sequence inhibits the MBP from being closed until the UPS is in
Bypass mode, preventing the bypass source and the UPS inverter from being
connected in parallel.
Key B is removed from the MBP, inserted into the key B slot on the MIS, and the MIS
opened. When the MIS is locked using key B, key A from the MIS to be removed and
inserted into the solenoid lock and locked in place. This inhibits the MIS from being
closed if the UPS is placed back online, preventing the bypass source and the UPS
inverter from being connected in parallel.
The UPS is in maintenance bypass and isolated from the the maintenance bypass
source until the sequence is reversed.
5.3
Normal Mode Current Flow
When the maintenance bypass breaker (MBP) is open and the maintenance isolation
switch (MIS) is closed, conditioned and protected power from the UPS is routed
through the MIS to the critical load.
If the optional bypass input breaker (BIB) is installed, power is supplied to the UPS
through the BIB, and the UPS rectifier is supplied from a separate feeder or the UPS
rectifier and bypass input terminals are jumpered together and both supplied by the
BIB. If the optional BIB and rectifier input breaker (RIB) are installed, the UPS rectifier
is supplied power through the RIB and the UPS bypass is supplied power through the
BIB, for a dual-feed system.
Figure 5‐1 shows the path of electrical power through the MBM when operating in
UPS mode.
MBM
RIB
(Optional)
BIB
(Optional)
MIS
MBP
AC Input to MBM
from Utility
To UPS Rectifier Input
From UPS Output
To UPs Bypass Input
Main Power Flow in UPS Mode
Main Power Flow in Maintenance Bypass Mode
Output To Critical Load
Figure 5‐1. Path of Current Through the MBM in UPS Mode
