Calculator Inputs
Example Data Table
Sample values below demonstrate typical temporary site loads.
| Description | Qty | Watts each | PF | Demand factor | Continuous |
|---|---|---|---|---|---|
| Temporary Lighting | 20 | 100 | 1.00 | 1.00 | Yes |
| Portable Tools | 6 | 1200 | 0.85 | 0.60 | No |
| Site Office HVAC | 2 | 2500 | 0.95 | 0.80 | Yes |
| Water Pump | 1 | 3000 | 0.90 | 0.70 | No |
Formula Used
Connected Power (W): W = Qty × WattsEach
Connected Load (kW): kW = W ÷ 1000
Demand kW per item: Demand kW = kW × DemandFactor × ContinuousMultiplier
ContinuousMultiplier = 1.25 when marked continuous, otherwise 1.00.
Apparent Power (kVA): kVA = Demand kW ÷ PF
Overall adjustment: Adjusted = Sum × OverallDemandFactor
Contingency: Final = Adjusted × (1 + Contingency% ÷ 100)
Estimated current:
- Single-phase: I = (kVA × 1000) ÷ V
- Three-phase: I = (kVA × 1000) ÷ (√3 × V)
How to Use This Calculator
- Select the system phase and enter the line voltage.
- Add each load item, including quantity and watts per unit.
- Set a demand factor for expected simultaneous usage.
- Enter a realistic power factor for motors and HVAC equipment.
- Mark continuous loads to apply 125% sizing automatically.
- Apply an overall demand factor and contingency if needed.
- Press calculate to view kW, kVA, and estimated current.
- Use CSV or PDF downloads for documentation and approvals.
Always verify site requirements with local standards and equipment nameplates.
Accurate load estimates keep projects powered, safe, and efficient.
Electrical Load Planning Guide
1) Why construction load planning matters
Temporary power is often expanded in phases, and underestimating demand can cause nuisance trips, voltage drop, and delayed work. This calculator helps you total connected kW, apply diversity, and size supply capacity with a documented margin. On busy sites, load profiles change daily. Recheck the schedule after major mobilizations, crane installation, or concrete pours. Keeping an updated demand figure supports breaker selection, feeder sizing, and clear communication during permit inspections and safety briefings.
2) Build a realistic load schedule
Start by listing lighting, office equipment, pumps, welders, and HVAC as separate line items. Enter nameplate watts for resistive loads and realistic running watts for motors. Use demand factors to reflect simultaneous use, such as 0.60 for tools that cycle and 0.80 for office HVAC.
3) Power factor and kVA implications
Current and generator sizing depend on kVA, not only kW. For example, a 7.0 kW welder at 0.80 power factor becomes 8.75 kVA. If your site is three-phase at 400 V, that single load draws about 12.6 A using I = (kVA×1000)/(√3×V).
4) Continuous loads and practical margins
Continuous circuits are commonly sized at 125% to prevent overheating and protect conductors. Mark lighting or always-on ventilation as continuous to apply the multiplier automatically. Then apply an overall demand factor for project-level diversity and add contingency (often 10–20%) to accommodate new tools, temporary cabins, or extended shifts.
5) Example scenario using project data
Suppose you have 20×100 W lighting (2.0 kW, continuous), 6×1200 W tools (7.2 kW, DF 0.60, PF 0.85), and 2×2500 W HVAC units (5.0 kW, DF 0.80, PF 0.95, continuous). The calculator converts each item to demand kW, then to kVA, and finally estimates line current. Export CSV or PDF to share with supervisors, electricians, and generator suppliers.
FAQs
1) Should I enter running watts or starting watts for motors?
Use running watts for normal operation. If starting current is a concern, add another temporary “starting allowance” row or increase contingency so the supply and protective devices can tolerate short inrush periods.
2) What demand factor should I use for hand tools?
For intermittent tools, many teams use 0.40–0.70 depending on crew size and workflow. Choose a value that reflects how many tools will run at the same time, not how many are on site.
3) Why does power factor change the result so much?
Lower power factor increases kVA for the same kW. Since current is calculated from kVA, poor power factor can push feeders and generators into overload even when kW looks reasonable.
4) When should I mark a load as continuous?
Mark loads expected to run for long periods, such as lighting, ventilation fans, or always-on control panels. The calculator applies 125% sizing to help reflect common continuous circuit design practice.
5) How do I size a generator from the output?
Use the suggested kVA as a starting point, then confirm with the generator vendor for transient response, altitude, temperature, and harmonics. If you have large motor starts or welders, add extra margin.
6) Can I mix single-phase and three-phase items in one schedule?
This sheet estimates totals for one selected system voltage and phase. If you have mixed systems, calculate separate schedules by distribution board, then combine results at the upstream supply point.
7) What should I do after exporting CSV or PDF?
Attach the report to your temporary power plan, include assumptions for demand factors and power factors, and update it whenever major equipment is added or removed. This keeps approvals and site safety discussions aligned.
Accurate load estimates keep projects powered, safe, and efficient.