Complete Guide to 3-Phase Load Calculation
The 3-Phase Load Calculator computes total kW, kVA, current, and balance. Detects imbalance >10%. Our free tool ensures NEC compliance and system reliability.
What is 3-Phase Load?
Three-phase power: P = √3 × V × I × PF. Balanced = equal per phase. Our 3-Phase Load Calculator handles unbalanced loads.
Why Balance Loads?
Benefits:
- Lower Neutral Current: Reduce heating.
- Transformer Life: Avoid derating.
- Compliance: NEC 310.15(B)(5).
- Efficiency: Less loss.
Use with Neutral Current and Load Balance.
3-Phase Formulas
- Total kW = A + B + C
- kVA = kW / PF
- Current = kVA × 1000 / (√3 × V)
- Imbalance % = (Max - Min) / Avg × 100
Load Types
| Type | Typical PF | Phase |
|---|---|---|
| Resistive (Heaters) | 1.0 | Any |
| Inductive (Motors) | 0.8 | Line-to-line |
| Lighting | 0.95 | Line-to-neutral |
| Receptacles | 0.9 | Line-to-neutral |
Imbalance Limits
| Component | Max Imbalance |
|---|---|
| Transformer | 10% |
| Panelboard | 20% |
| Neutral | 100% of phase |
Calculation Steps
- Measure: kW per phase.
- Sum: Total kW.
- Apply PF: kVA.
- Current: I = kVA × 1000 / (√3 × V)
- Check Balance: <10%.
Example: Factory Panel
480V, Phase A: 50 kW, B: 60 kW, C: 40 kW, PF 0.85.
- Total kW = 150 kW
- kVA = 150 / 0.85 = 176.5 kVA
- I = 176.5 × 1000 / (1.732 × 480) = 212 A
- Imbalance = (60-40)/50 × 100 = 40% → Unbalanced!
How to Balance
- Redistribute: Single-phase loads.
- Use 3-Phase: Motors, HVAC.
- Monitor: CTs, meters.
- Auto Transfer: Load management.
Practical Applications
For:
- Factories: Motors, welders.
- Commercial: Lighting, receptacles.
- Data Centers: Servers.
- EV Stations: Charging.
Tips
- Measure PF: Per phase if different.
- Derate: >10% imbalance.
- Neutral Sizing: 200% if nonlinear.
- Log Data: Trend imbalance.
Common Mistakes
- Assume Balance: Without measuring.
- Ignore PF: Wrong kVA.
- Wrong Voltage: L-N vs L-L.
- No Spare: Future loads.
Advanced Topics
- Vector Sum: For currents.
- Harmonics: 3rd in neutral.
- Power Quality: Voltage unbalance.
- NEMA MG-1: Motor derating.
Conclusion
Balanced 3-phase loads improve efficiency and equipment life. Our 3-Phase Load Calculator instantly flags imbalance. Combine with Neutral Current and Construction tools. Optimize with 1000 Calculators.