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6.2 Bypass Mode
If the UPS unit is severely overloaded or develops an internal fault, power flow is automatically
switched from the main circuit to the Bypass circuit. Power flow through the bypass is shown in the
following illustration. This changeover occurs automatically in less than 4 milliseconds in phase
(Make-Before-Break). If the power flow is transferred to the Bypass circuit because of an overload
and that overload condition ends within a specified period of time, then the power flow will "re-
transfer" to the AC Input Mode (Normal Operation) automatically. If the power flow is transferred to
the Bypass circuit due to a fault condition, then the power flow must be transferred manually
from the UPS's Bypass circuit back to the Inverter circuit after repairing the fault (see "Start-up
Procedure"). If the power flow is transferred to the Bypass circuit due to an overload condition,
then the power flow will automatically transfer from the UPS's Bypass circuit back to the
Inverter circuit after removing the overload (see "Overload Operation").
Input
Power
Converter Inverter
Bypass
Charger/
Chopper
Isolating
XFMR
External
Batteries
Output
Power
MCCB
MBS
Power Flow
Power flow in Bypass mode
6.3 Bypass Mode for Optional Alternate Input Models
Power flow in Bypass mode for the Alternate Input Models
Power Flow
Converter Inverter
Bypass
Charger/
Chopper
Isolating
XFMR
External
Batteries
Output
Power
MCCB
MBS
Bypass
Power
Input
Power
4200FA CT/XT User’s Manual 38