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2026-09-22
ACwatt| Term | Meaning | Why it matters |
|---|---|---|
| kVA | Apparent power | Electrical capacity |
| kW | Real power | Usable load power |
| Power factor | Relationship between kVA and kW | Determines usable capacity |
| Application | ACwatt direction | Information needed |
|---|---|---|
| Rack servers | ACS 1–3kVA | Load, voltage, space, runtime |
| Large three-phase loads | ACM modular UPS | kW/kVA, voltage, growth, redundancy |
| Critical facilities | ACM 100–1200kVA | Load profile, battery and site conditions |
UPS capacity starts with two numbers
Choosing a UPS is not only a matter of matching the nameplate kVA to connected equipment. A reliable selection checks apparent power in kVA and real power in kW. The power factor links the two values: kW = kVA × power factor.
For example, a 10kVA load at a power factor of 0.9 requires approximately 9kW of real power. A load with a power factor close to 1.0 can use more of the rated UPS capacity as usable kW. The final selection should also account for peak demand, growth, battery runtime and redundancy.
What is the difference between kVA and kW?
kVA describes the voltage and current supplied by the UPS. kW describes the real power consumed by servers, network equipment, controls and other loads. A UPS can be rated at 10kVA, but its usable kW depends on its output power factor.
A practical UPS sizing method
- List normal and peak load in kW.
- Convert the load into kVA where required.
- Confirm voltage, phase and output power factor.
- Add an approved allowance for future growth.
- Choose single, parallel or redundant operation.
- Select the battery system and runtime separately.
ACwatt capacity options
The ACS Series 1–3kVA online rack UPS is designed for servers, network equipment and other single-phase rack loads. The public product page lists 1kVA/1kW, 1.5kVA/1.5kW, 2kVA/2kW and 3kVA/3kW models with a 1.0 output power factor.
For larger three-phase requirements, the ACM Series 100–1200kVA uses 100kVA/100kW power modules. The public page lists AC600/100E, AC800/100E and AC1200/100E. Final configuration depends on load, redundancy, battery runtime, cabinet selection and project conditions.
Worked example
Assume a critical IT load of 72kW at a power factor of 0.9. The apparent power is approximately 80kVA. The final UPS should not be selected from this number alone. Confirm the exact model output power factor, growth allowance, overload requirement and redundancy plan.
Information to include in an RFQ
- Normal and peak load in kW and kVA.
- Input and output voltage and phase.
- Required battery runtime.
- Expected load growth.
- Parallel or N+1 requirement.
- Lead-acid or lithium battery preference.
Frequently Asked Questions
Can a 10kVA UPS deliver 10kW?
Only when its output power factor is 1.0 and the operating conditions support the rated output.
Is higher kVA always better?
No. Oversizing can increase cost and reduce the value of the installation. Match the rating to load, growth, runtime and redundancy.
What does ACwatt need for model selection?
A load list, voltage and phase, runtime, battery preference, growth plan and redundancy requirement.
Source: ACS Series 1–3kVA Online Rack UPS
Source: ACM Series 100–1200kVA Modular UPS
Need help selecting a UPS?
Share your load profile, voltage, required runtime and redundancy target with ACwatt.
