In short. A load list is the foundation of every sizing decision. It records each load’s rating, voltage, power factor, duty and starting method. Built well, it feeds generator, transformer, UPS and cable sizing. Built badly, every downstream number is wrong.
Core relationships
kVA = kW ÷ power factor
kVAr = √(kVA² − kW²)
For a motor, shaft power is not the electrical input. Input kW = shaft kW ÷ efficiency, and kVA = input kW ÷ power factor. A 30 kW motor at 92 per cent efficiency and 0.86 power factor draws about 32.6 kW and 37.9 kVA.
Recommended columns
| Column | Why it matters |
|---|---|
| Load name and tag | Traceability |
| Voltage and phases | Distribution design |
| Rated kW (shaft or output) | Starting point |
| Efficiency and power factor | Convert to electrical input |
| Input kW, kVA, kVAr | Sizing inputs |
| Duty: continuous, intermittent, standby | Diversity |
| Starting method and starting current | Generator and voltage dip |
| Criticality class | UPS, generator and shedding decisions |
| Source: nameplate, measured or estimated | Confidence |
Where the numbers come from
- Measured: best. Use a power analyser over a typical period, including peaks.
- Nameplate: gives rating, not actual load, which is often lower.
- Manufacturer data: for specified equipment.
- Estimates: flag them clearly and review later.
Connected versus running load
Connected load is the sum of all ratings. Running load is what actually draws power at a time. The difference depends on duty cycles, spares and standby units. See maximum demand and diversity.
Worked example (illustrative)
Three loads: a 30 kW motor (eff. 0.92, pf 0.86), 20 kW of lighting and small power (pf 0.95) and a 15 kW heater (pf 1.0). Input kW: 32.6 + 20 + 15 = 67.6 kW. kVA: 37.9 + 21.1 + 15 = 74.0 kVA. Combined pf = 67.6 ÷ 74.0 ≈ 0.91. The method of adding kVA arithmetically is conservative; adding kW and kVAr, then taking the root of the sum of squares, is more accurate. Here kVAr: 19.3 (motor) + 6.6 (lighting) + 0 = 25.9, giving kVA = √(67.6² + 25.9²) ≈ 72.4. The difference is small but grows with many loads.
Keeping the list useful
- Date it and record the author.
- Update when loads change; version it.
- Use it as the single source for all sizing.
- Mark loads by class so shedding and UPS lists can be drawn from it.
Building the connected load table
| Column | Source | Why |
|---|---|---|
| Equipment and tag | Site survey, drawings | Traceability |
| Rated kW | Nameplate | Starting point |
| Efficiency, power factor | Datasheet | Convert to input kVA |
| Quantity and duty | Operator | Running and standby counts |
| Starting method | Panel inspection | For motor-start checks |
| Class | Operator agreement | Generator-backed or not |
Worked example (illustrative)
Three pumps of 30 kW, two running and one standby. Motor efficiency 0.92, power factor 0.85. Input kVA each = 30 ÷ (0.92 × 0.85) ≈ 38.4 kVA. Running load = 2 × 38.4 = 76.7 kVA. The standby pump is not counted in running demand but is kept in the connected total for reference.
Pitfalls
- Using shaft kW as input kW.
- Counting standby units as running loads, which oversizes the plant.
- Missing seasonal loads such as summer air conditioning.
- Forgetting lift motors, fire pumps and small distributed loads that add up.
Check against reality
Compare the total with the utility bill’s maximum demand or a logged week. A gap above about 15 percent needs explanation.
See load inventory and maximum demand and diversity guide.
Common mistakes
- Using shaft kW as input kW.
- Mixing kW and kVA in one total.
- Counting standby and duty units together without a duty flag.
- Forgetting small loads that add up, such as control panels and lighting.
What to send us
Send your load list or the equipment schedule. Send your application details. See also load inventory.
Questions engineers ask
What is the difference between kW and kVA?
kW is real power doing work. kVA is apparent power, the product of voltage and current. They are related by power factor.
Why does power factor matter for sizing?
It changes the kVA the generator or transformer must supply for the same kW.
Should I use nameplate or measured values?
Measured where possible; nameplate gives an upper bound and often overstates actual load.
How do I treat standby equipment?
List it but mark its duty so it is excluded from running load, and include it where it may run during a changeover.
Figures are illustrative. Check the numbers against your own equipment data.