Critical vs Non-Critical UPS Loads
Q: What is the difference between critical and non-critical UPS inverter loads?
A: A critical load is one that must be protected by the UPS from power failures and bad utility supply — it requires inverter and battery backup when mains fails. A non-critical load is anything that does not need to keep running when mains fails.
Sizing approach: list every load that needs UPS protection, treat that list as the absolute minimum, and do not include luxuries. Battery cost rises non-linearly with kW protected, so even small additions to the critical-load list have material capital and TCO impact.
Power-draw calculation:
- Read each device’s power rating from its rating plate (typically rear or underside) or off the power supply
- Sum the ratings — this is the total critical load in Watts
- Add 30% headroom for inrush during start-up
- Convert Watts to VA by dividing by 0.7 (typical PF assumption)
- Select a UPS sized to that VA target — but not so large that running load is below 50% (running 25–50% loaded is inefficient)
Connections
- FAQ - How to Size a UPS — relates, source: https://standbysystems.co.za/ups-batteries-questions-and-answers/