Quick Answer
For construction sites, typical generator sizes range from 20-500 kVA. The critical sizing factor is mobile requirements, welder and crane inrush, variable loads. Always calculate both running kW and starting kVA, apply appropriate diversity factors, and add 20% growth margin for future expansion.
Generator Sizing for Construction Sites — Complete Guide (2026)
Proper generator sizing for construction sites is essential for reliable power. This comprehensive guide covers everything you need to know to select the right generator size.
Power Requirements for Construction Sites
Construction Sites applications have specific power requirements that must be understood before sizing. The load profile typically includes a mix of resistive and inductive loads with varying duty cycles.
Sizing Methodology for Construction Sites
Step 1: Complete a detailed load survey. Step 2: Separate running loads from starting loads. Step 3: Calculate total running kW with diversity factor. Step 4: Add the largest motor starting kVA. Step 5: Apply environmental de-rating factors. Step 6: Add growth margin and select standard size.
| Parameter | Value | Notes |
|---|---|---|
| Application | Construction Sites | Specific sizing considerations apply |
| Typical Size | 20-500 kVA | Varies with specific requirements |
| Diversity Factor | 0.6-0.9 | Depends on load coincidence |
| Growth Margin | 20% | Standard for new installations |
| Phase | 1 or 3 | Based on load types |
| Frequency | 50 or 60 Hz | Region dependent |
| Load Component | % of Total | Starting Factor |
|---|---|---|
| Motor Loads | 40-60% | 3-7x |
| Resistive Loads | 20-30% | 1x |
| Lighting | 10-20% | 1x |
| Electronics/IT | 5-15% | 1-2x |
Key Takeaways
- Always calculate both running kW and starting kVA — the larger value determines generator size.
- Motor starting current (3-7x running) is typically the limiting factor, not steady-state load.
- Apply diversity factor (0.6-0.9) based on application. Never assume 100% simultaneous load.
- Add 10-25% growth margin. Industrial: 20% minimum. Data centers: 25% minimum.
- De-rate for altitude above 1000m and ambient temperature above 40°C per manufacturer tables.
- For motor-heavy loads, choose PMG excitation and low sub-transient reactance alternators (X''d <12%).
- For Construction Sites, the typical generator size range is 20-500 kVA.
- Key consideration: Mobile requirements, welder and crane inrush, variable loads.
Summary
Proper generator sizing is the foundation of reliable backup power. By calculating both steady-state running loads and transient starting requirements, applying appropriate diversity factors, and accounting for environmental conditions, you ensure the generator delivers reliable power without wasteful oversizing. A correctly sized generator provides the right balance of capability, efficiency, and cost.
Frequently Asked Questions
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