Complete Guide to Neutral Current
The Neutral Current Calculator computes neutral amps in 3-phase systems. Balanced = 0A, unbalanced + harmonics = oversized neutral.
What is Neutral Current?
In 3-phase: Iₙ = √(Iₐ² + I_b² + I_c² - Iₐ·I_b - I_b·I_c - I_c·Iₐ). Harmonics: 3rd order adds in neutral. Our Neutral Current Calculator handles both.
Why Size Neutral?
Prevents:
- Overheating: Neutral > phase.
- Tripping: GFP breakers.
- Fire: Undersized neutral.
- Code Violation: NEC 310.15(B)(5).
Use with 3-Phase Load and Harmonics.
Neutral Sizing Rules
| Condition | Neutral Size |
|---|---|
| Balanced | 0% (no neutral) |
| Unbalanced < 50% | 100% of phase |
| > 50% nonlinear | 200% of phase |
| High 3rd harmonic | 173% theoretical |
Harmonic Impact
3rd, 9th, 15th → add in neutral. Iₙ = I_phase × √3 × (%3rd/100).
| Load | 3rd Harmonic % |
|---|---|
| PCs, Servers | 60–90% |
| LED Lighting | 20–40% |
| VFDs | 30–50% |
| Fluorescent | 15–25% |
Calculation Methods
- Vector Sum: For unbalanced.
- 3rd Harmonic: Iₙ = I_phase × 1.732 × (%3rd/100).
- Full Phasor: Complex angles.
Example: Office Panel
Phase A: 50A, B: 70A, C: 60A, 30% 3rd harmonic.
- Vector: Iₙ = √(50² + 70² + 60² - 50×70 - 70×60 - 60×50) = 34.6A
- Harmonic: 60A × 1.732 × 0.3 = 31.2A
- Total ≈ 46A → Use 200% neutral
Neutral Sizing
- Linear: 100%.
- Nonlinear >50%: 200% (NEC 310.15(B)(5)(c)).
- Derate: If in same raceway.
Practical Applications
For:
- Data Centers: High harmonics.
- Offices: PCs, lighting.
- Factories: VFDs.
- Hospitals: Sensitive loads.
Tips
- Measure: Use true-RMS clamp.
- Separate: Neutral per phase.
- K-Rated: Transformers.
- Filters: Reduce 3rd.
Common Mistakes
- Assume 0A: Even balanced.
- Ignore Harmonics: Nonlinear loads.
- Shared Neutral: Multi-wire.
- No GFP: Required >1000A.
Advanced
- Phasor Diagram: Vector sum.
- Triplen Harmonics: Zero sequence.
- Neutral Bonding: Only at service.
- Monitoring: IoT sensors.
Conclusion
Neutral current is often overlooked but critical. Our Neutral Current Calculator flags high neutral for safety. Pair with 3-Phase Load and Construction tools. Stay safe with 1000 Calculators.