Understanding IAC Operation
4-2
EATON
Powerware
®
9390 IAC-B and IAC-T Installation and Operation Manual
S
164201590 Rev C
powerware.com
4.1.2 Maintenance Bypass Mode
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 4-2 shows the path of electrical power through the IAC when operating in
Maintenance Bypass mode.
OUTPUT TO
CRITICAL LOAD
IAC
RIB
(OPTIONAL)
BIB
(OPTIONAL)
MIS
MBP
TO UPS RECTIFIER
INPUT
FROM UPS OUTPUT
TO UPS BYPASS
INPUT
MAIN POWER FLOW IN UPS MODE
MAIN POWER FLOW IN MAINTENANCE BYPASS MODE
AC INPUT TO
UPS FROM
UTILITY
AC INPUT TO
BYPASS FROM
UTILITY
Figure 4-2. Path of Current Through the IAC in Maintenance Bypass Mode
Summary of Contents for Powerware 9390 IAC-B
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