Panel Schedule & Load Balancing Calculator

Calculate panelboard phase loads (Phase A/B/C), percentage phase imbalance, neutral current, and bus utilization per NEC §408.4.

NEC edition

Inputs

VA
VA
VA
%

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⚡ Test your knowledge
NEC Article 220 was renumbered in the 2026 code cycle. What is the new article number?
  • A. Art. 100
  • B. Art. 120
  • C. Art. 200
  • D. Art. 230
💡 NEC 2026 renumbered Article 220 (Branch-Circuit, Feeder, and Service Calculations) to Article 120.
Energy Management Systems were moved from Article 750 to which article in NEC 2026?
  • A. Art. 100
  • B. Art. 125
  • C. Art. 130
  • D. Art. 150
💡 NEC 2026 moved Energy Management Systems from Article 750 to Article 130.
Which NEC standard size overcurrent device comes after 90A?
  • A. 95A
  • B. 100A
  • C. 110A
  • D. 105A
💡 Per NEC §240.6(A), the standard sizes are …90, 100, 110, 125… There is no 95A standard size.

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How it works & the NEC rules behind it

Under NEC §408.4, every panelboard circuit must be legibly identified in an updated directory. Distributing branch circuit loads evenly across phases (Phase A, B, and C) is essential to minimize neutral return currents, avoid harmonic heating, and prevent single-phase busbar overload trips.

Core Panel Schedule Metrics:

  • Phase Imbalance (%): Calculated as [(Max Phase VA − Min Phase VA) ÷ Average Phase VA] × 100%. IEEE standards recommend keeping imbalance under 10%.
  • Neutral Current (3-Phase): In 3-phase Wye systems, balanced 120V loads cancel in the neutral conductor. When unbalanced:
    I_neutral = √(I_A² + I_B² + I_C² − I_A·I_B − I_B·I_C − I_C·I_A).
  • Neutral Current (1-Phase 120/240V): Equal to the absolute difference between Phase A and Phase B: I_neutral = |I_A − I_B|.
  • Panel Bus Utilization: Computed as (Max Phase Current ÷ Panel Main/Bus Rating) × 100%.

Formulas & equations

Phase Imbalance (%) = [(Max Phase VA − Min Phase VA) ÷ Average Phase VA] × 100% 1-Phase Neutral Amps = |I_A − I_B| (§120.61 / §220.61) 3-Phase Neutral Amps = √(I_A² + I_B² + I_C² − I_A·I_B − I_B·I_C − I_C·I_A) Bus Utilization (%) = (Max Phase Current ÷ Bus Rating) × 100%

NEC reference table

Imbalance Level Phase Delta % System Impact Recommended Action
Excellent (Ideal)0% – 5%Minimal neutral heating, optimum voltage stabilityKeep circuit assignments
Acceptable5% – 10%Standard commercial/residential operationAcceptable per IEEE standard
High Imbalance> 10%Excessive neutral current, voltage drop unbalance, breaker trippingRe-assign 120V single-pole circuits between phases

Worked example, step by step

Example: 3-Phase 120/208V 225A Commercial Distribution Panel

Given: Connected loads: Phase A = 18,500 VA, Phase B = 16,200 VA, Phase C = 17,800 VA.

  • 1. Average Phase Load: (18,500 + 16,200 + 17,800) ÷ 3 = 17,500 VA.
  • 2. Phase Imbalance: [(18,500 − 16,200) ÷ 17,500] × 100% = 13.1% (High imbalance).
  • 3. Phase Currents (@ 120V L-N): I_A = 154.2A, I_B = 135.0A, I_C = 148.3A.
  • 4. Neutral Current: √(154.2² + 135.0² + 148.3² − 154.2·135 − 135·148.3 − 148.3·154.2) = 17.0 Amps.
  • 5. Bus Utilization: 154.2A ÷ 225A = 68.5%.

Frequently asked questions

Unbalanced phase loads cause uneven heating in transformers and panel busbars, increase neutral conductor return currents, and cause voltage unbalance that can damage 3-phase induction motors.

In linear 60Hz systems with purely sinusoidal loads, neutral current cannot exceed the maximum phase current. However, where non-linear harmonic loads (such as LED drivers, computers, and VFDs) generate triplen harmonics (3rd, 9th, 15th), neutral current can reach up to 173% of phase current per NEC §120.61(C) / §220.61(C).

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