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ITGlossary · UPS technology
Zero Transfer Time
A feature of online UPS systems, where the inverter feeds the load continuously so a power cut causes no gap at all.
Technical level:Intermediate
In double-conversion (online) UPS units the inverter powers the load continuously. The mains feeds the rectifier, which supplies DC to the inverter and charges the batteries. When the power fails, the battery takes over supplying the inverter without anything changing at the output, so there is no transfer and no gap.
This matters for servers, medical and laboratory equipment, industrial controllers and any load that cannot tolerate even a few milliseconds of interruption. Line-interactive UPS units, by contrast, typically have a transfer time of a few ms.
Check exactly what a 0 ms specification refers to. It concerns the transfer from mains to battery. The transfer to bypass, in the event of overload or a fault, may involve a short delay on some models.
Related terms
- Online (Double Conversion) UPSA UPS that continuously converts incoming AC to DC and back to AC, so the load is always fed by the inverter with clean, stable power.
- InverterThe component inside a UPS that converts DC power from batteries back to usable AC power.
- Transfer TimeThe brief power gap when a UPS switches from mains to battery, typically 2–10 ms for line-interactive models and zero for online ones.
- AutonomyThe time a battery-powered system (like a UPS) can continue operating critical loads after a power failure.
- Auto RestartA UPS feature that automatically restarts the system after utility power returns following a shutdown.
- Double Conversion EfficiencyThe share of input power that an online UPS delivers to its output, lower at light load and highest at medium to high load.