Which relationship should the drafter preserve?
Schneider Electric defines UPS efficiency as output electrical power divided by input electrical power and notes that efficiency varies with loading. Record the manufacturer's actual mode, load point and measurement boundaries when transferring those values to a schedule.
Critical Power Drafting is independent and is not affiliated with Schneider Electric. This guide reconciles approved information. It does not size an upstream circuit, choose an operating mode or substitute for the engineer's design.
Sources: Schneider Electric: What is UPS efficiency and how is it calculated? Updated 11 June 2025
What does an input-output worksheet need?
Compare the same UPS tag and approved submittal revision. A nameplate output capacity and an efficiency value taken at a different loading point are not a complete input-demand calculation. Preserve charging, auxiliary and other stated conditions rather than assume they are included.
| Field | Evidence | Review action |
|---|---|---|
| Output | Approved real load and output boundary | Do not relabel kVA as kW |
| Input | Manufacturer input data and stated conditions | Identify supply-side boundary |
| Efficiency | Value, load point and mode | Use the matching operating case |
| Losses | Source and calculation basis | Keep separate from output load |
| Other demand | Charging or auxiliaries and their inclusion | Avoid omission or double counting |
| Drawing reference | SLD, schedule and mechanical interface revision | Escalate conflicting cases |
Why is the loss not simply a percentage of output?
Illustrative example. A fictional steady operating case supplies 95 kW at its output and has 95 percent efficiency across the stated AC input-output boundary. Input is 95 / 0.95 = 100 kW. The difference is 5 kW. These values are invented for arithmetic and are not a product rating.
Multiplying output by 5 percent gives 4.75 kW, which is not the input-output difference for this example. The efficiency denominator is input. Do not use this simplified case for battery charging, a transient, overload, bypass operation or an unverified auxiliary load.
What must happen before the schedule is issued?
Check that electrical and mechanical schedules refer to the same approved condition. Ask the manufacturer or engineer to resolve a missing input-demand or heat-rejection basis. A derived loss number is not evidence of room cooling capacity, protective-device suitability or generator performance.
Retain the source calculation and engineering disposition with the drawing change. Engineering sign-off is performed only by the registered engineer on the job.
Common questions
What else should the bid team know?
Is UPS efficiency the same as load power factor?
No. Efficiency compares input and output real power; power factor relates different electrical quantities.
Can one efficiency value describe every operating mode?
Use the actual manufacturer value for the stated mode and load point.
Can this example size the upstream breaker?
No. Upstream design requires the approved equipment and engineering inputs.
Primary sources
- What is UPS efficiency and how is it calculated? Updated 11 June 2025Schneider Electric