Undersized backup is one of the most common reasons systems still go down during load-shedding. A UPS that is too small trips under load; batteries that are too small run flat before the grid returns. Here is the approach our engineers use.
1. List what must stay on
Separate critical loads (servers, network, security systems, key workstations) from loads that can wait. Backing up everything is expensive; backing up the right things is not.
2. Measure the real load
Nameplate ratings overstate consumption. Measure live load with a clamp meter over a normal working day, and note the peak.
3. Add headroom and convert to kVA
Add roughly 25% headroom for growth and start-up surges, then choose the next standard UPS size up. Running a UPS near 100% shortens its life.
4. Size batteries for the outage, not the brochure
Battery capacity (kWh) ≈ load (kW) × hours of backup needed ÷ usable fraction of the battery. Allow for battery ageing and temperature.
5. Prove it
A battery run-down test under real load is the only way to know your backup time. Repeat it as part of maintenance.
Want a quick estimate first? Try our UPS & solar sizer, then ask an engineer to confirm it with a load study.