UPS stands for uninterruptible power supply. It uses an energy-storage path, switching and power conversion to support a connected load when normal input power is interrupted or unsuitable. Its watt and VA ratings are load limits; runtime depends on battery condition, connected load, design and operating conditions.
Simple explanation
A UPS can keep supported equipment running briefly through a power interruption, often long enough for continuity or controlled shutdown. Models differ in capacity, waveform, transfer behavior, monitoring and battery arrangement.
A UPS is not unlimited emergency power and does not replace correct earthing, surge planning or electrical installation.
Technical context
Check both real-power capacity in watts and apparent-power capacity in volt-amperes. The load must remain inside every applicable rating with suitable headroom.
Runtime cannot be calculated reliably from VA alone. Battery energy, inverter efficiency, age, temperature, load curve and manufacturer data affect the result.
Practical example
A computer, monitor and network device should be measured or conservatively estimated as a combined load. Use the exact UPS runtime chart for that load; do not assume a higher VA label guarantees a particular number of minutes.
Sources and further reading
Technical statements were reviewed against these references. External pages may change after our review date.
- Uninterruptible Power Supplies — U.S. Department of Energy
- UPS buying guide: Choose the right battery backup — Schneider Electric