4.3. Bypass Mode
UPS transfers the loads automatically to the mains voltage in order to protect them during abnormal condi-
tions.
While UPS operates in Online Operation, UPS switches to bypass automatically (in case the mains voltage
and frequency is within the limits of bypass) in the following conditions;
• During start-up
• Bypass Priority
• Inverter Fault
• Prolonged Overload, output short circuit
• High Heatsink Temperature
After these conditions are eliminated, the UPS automatically returns to inverter.
Bypass Operation Voltage Range
The mains voltage is required to be in certain range for Bypass Operation. Voltage tolerance is set 18% of
the output voltage in the factory. For instance; if the output voltage is Ph-Ph: 400V, the tolerance range of
bypass voltage would be Ph-Ph: 328V – 472V. In case the input voltage decreases below Ph-Ph: 328V or in-
creases above Ph-Ph: 472V; if UPS runs in Bypass Mode UPS switches to Online Mode Operation; if UPS runs
in Online Mode Operation it cannot switch to Bypass Mode Operation even if a fault occurs. If the batteries
and the inverter are suitable to supply the loads, UPS switches to Battery Mode Operation.
Bypass Mode Operation voltage tolerance limit can be adjusted in certain ranges depends on the cus-
tomer’s request on site by Legrand UPS Technical Service Personnel.
To return to Bypass Mode Operation; the mains voltage should turn back to +5V above of lower limit, -5V
down of upper limit of bypass limits. Default settings are Ph-Ph: 333V – 465V for Ph-Ph: 400V UPS.
Prolonged overloads in Bypass Operation may cause the thermal/magnetic pro-
tection act. In this case, all loads will be de energized.
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