Calculator Inputs
Example Data Table
| Load Category | Example Value | Unit | Purpose |
|---|---|---|---|
| Construction Area | 4,500 | sq ft | Used with general load density. |
| General Load Density | 1.50 | W/sq ft | Represents broad area demand. |
| Lighting Load | 6,000 | W | Temporary lights and task lights. |
| Tool Load | 15,000 | W | Portable construction equipment. |
| Motor Load | 12,000 | W | Hoists, pumps, mixers, or compressors. |
| Voltage | 400 | V | Three phase temporary supply. |
| Demand Factor | 0.85 | ratio | Reduces full connected coincidence. |
| Safety Margin | 15 | % | Adds spare capacity for planning. |
Formula Used
General Area Load (W) = Area (sq ft) × General Load Density (W/sq ft)
Connected Load (W) = General Area Load + Lighting + Receptacles + HVAC + Motors + Tools + Site Office + Other Loads
Maximum Demand (W) = Connected Load × Demand Factor ÷ Diversity Factor
Continuous Design Load (W) = Maximum Demand × Continuous Load Multiplier
Final Design Load (W) = (Continuous Design Load + Motor Starting Adder) × (1 + Safety Margin)
Apparent Load (kVA) = Final Design Load ÷ (1000 × Power Factor)
Single Phase Current (A) = Final Design Load ÷ (Voltage × Power Factor)
Three Phase Current (A) = Final Design Load ÷ (√3 × Voltage × Power Factor)
This calculator is intended for planning and preliminary sizing. Final feeder size, breaker rating, voltage drop checks, conductor derating, and equipment coordination must be verified against your project drawings, local electrical code, and manufacturer documentation.
How to Use This Calculator
- Enter the project name, site area, and general load density.
- Add known watt values for lighting, receptacles, HVAC, motors, tools, office loads, and other temporary equipment.
- Select the site voltage and choose single phase or three phase supply.
- Set realistic power factor, demand factor, and diversity factor values.
- Apply your continuous loading percentage and safety margin.
- Use a motor start multiplier if a large motor creates startup stress.
- Press the calculate button to view results above the form.
- Export the summary as CSV or PDF for reports, reviews, or client discussions.
Frequently Asked Questions
1) What does connected load mean?
Connected load is the total of all listed electrical loads before applying demand, diversity, or spare capacity adjustments. It represents the full installed wattage if every listed item ran together.
2) Why use a demand factor?
Demand factor reflects that many construction loads do not operate at full capacity at the same time. It helps estimate a more realistic operating demand instead of assuming constant full use.
3) Why is diversity factor separate?
Diversity factor accounts for noncoincident operation between multiple loads or groups. A higher diversity factor reduces maximum simultaneous demand because not every device reaches peak use together.
4) What is the motor starting adder for?
Large motors can draw extra current during startup. The motor starting adder gives the design load more breathing room, which is useful when sizing temporary supplies and backup generators.
5) Is the feeder size output final?
No. The feeder suggestion is only a preliminary planning guide. Final conductor size depends on ampacity tables, insulation type, ambient temperature, grouping, installation method, and code requirements.
6) Can I use this for generators?
Yes. The calculator provides an estimated generator kVA recommendation based on final design load and a small extra allowance. You should still review starting currents and manufacturer sizing notes.
7) What voltage should I enter?
Enter the actual supply voltage planned for the temporary construction system, such as 120 V, 230 V, 240 V, 400 V, or 415 V. Match the selected phase type to that supply.
8) Does this replace a licensed electrical design?
No. This tool is for early planning, budgeting, and quick checks. Permit drawings, protection studies, panel schedules, and final code compliance still require qualified project review.