Emerson Liebert NX 50 and 60 Hz - Manual (Page 64)

External Optional Cabinets
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4.0 E XTERNAL O PTIONAL C ABINETS
4.1 External Maintenance Bypass Cabinets
The bypass cabinet enables maintenance operations and repairs to be performed in full isolation
while also allowing the disabling of each UPS without affecting the ordinary operation of the system
(depending on the redundancy level).
The optional maintenance bypass cabinet must be used in all configurations where one internal main-
tenance bypass switch is insufficient to supply the full system load.
Each kVA rating has maintenance bypass cabinets sufficient to supply the full system load up to six
units in parallel power operation.
4.2 Interlock with UPS Module
Interlock the External Maintenance Bypass Switch with the operation of the UPS module(s) prevents
backfeed of the External Bypass AC power into the Inverter if an incorrect switching sequence is
used. A volt-free auxiliary status contact from external bypass switch QF3 is connected to UPS termi-
nal X3 (MBC interface) of the parallel control board (M3).
Figure 35 External maintenance bypass cabinet with separate bypass input
4P
4P
400V, 50Hz
4W
S
Q1
Q2
Q3
Q5
X3
X1
CB
4P
Q1
Q2
Q3
Q5
X3
X1
CB
4P
UPS2
UPS3
400V, 50Hz
3 or 4W
400V, 50Hz
4W
Supplied
by Others
Q1
Q2
Q3
Q5
X3
X1
CB
4P
UPS1