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Figure 28 External maintenance bypass switch, single-input UPS
The table below summarizes the External Maintenance Bypass switch positions and actions.
When the External Maintenance Bypass switch is in Bypass or Maintenance position, the UPSC will
assert the bypass contactor close signal and the output contactor open signal. It will also turn on the
SBS. Automatic Retransfer operations will be disabled.
If the External Maintenance Bypass switch rotates from the Bypass or Maintenance to the Normal
position, then the UPSC will keep the bypass in the ON state, thus keeping the critical bus powered
via the bypass source. The user will be able to issue a “Manual Transfer to Inverter” command pro-
vided the retransfer conditions are satisfied. The user can also issue a shutdown or a start command.
If the External Maintenance Bypass switch rotates from the Normal to the Bypass or Maintenance
position, the UPSC will assert the bypass contactor close signal and the output contactor open signal.
It will also turn on the SBS. Automatic Retransfer operations will be disabled.
Table 3 External maintenance bypass switch positions and actions
Switch position S1-A S1-B S1-C AUX
Maintenance (Service) Open Closed Open Open
Test (Bypass) Closed Closed Open Open
On Line (Transition) Closed Closed Closed Open
On Line (Normal) Closed Open Closed Closed
S1-A
S1-B
S1-C
SBS
Rect INV
Battery
Critical load
UPS Input
IMBS