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Ag Electrical Load Panel Planner - NEC Demand Factors for Farm Buildings

Size service entrances, panels, transformers, and conductors using NEC Article 220 & 430

Plan electrical service for farm shops, grain handling facilities, livestock confinement buildings, and dairy operations using NEC demand factors. Enter your loads (motors, heaters, lighting, receptacles, welders, EV chargers) and get service entrance amperage, panel size, conductor sizing per NEC 310.16, and transformer kVA requirements. Includes NEC motor FLA tables (430.248/250) and automatic 125% largest motor adder per NEC 430.24.

Pro Tip: The NEC 430.24 rule (125% of the largest motor + 100% of all others) is what catches most people on motor-heavy buildings like grain handling. One 15HP motor changes the entire feeder calculation.

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Electrical Load Panel Planner - Farm/Ag
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How It Works

  1. Select Service Configuration

    Choose your service voltage: 120/240V single-phase, 120/208V three-phase, or 277/480V three-phase. This determines amp calculations and motor voltage options.

  2. Add Your Loads

    Use a building template (farm shop, grain handling, livestock, dairy) or start blank. Add individual loads with type, rating, and continuous/non-continuous classification.

  3. Review NEC-Based Results

    See connected load, demand load after NEC 220 factors, service entrance amps, minimum panel size, conductor size per NEC 310.16, and transformer kVA. Each load shows individual conductor sizing.

Built For

  • Farmers planning new building electrical service
  • Electricians sizing service for agricultural customers
  • Utility companies estimating transformer requirements
  • Engineers designing farm facility electrical systems

Assumptions

  • Motor full-load ampere (FLA) values follow NEC Tables 430.248 (single-phase) and 430.250 (three-phase)
  • The largest motor receives a 125% multiplier per NEC 430.24 for motor feeder sizing
  • Demand factors follow NEC Article 220 standard calculations (general lighting first 10 kVA at 100%, remainder at 50%)
  • Conductor sizing uses NEC Table 310.16 for 75 degrees C rated insulation at 30 degrees C ambient
  • Continuous loads are factored at 125% per NEC 210.20 and 215.3 for overcurrent protection and feeder sizing
  • Voltage drop is not calculated — the user must verify conductor length does not exceed NEC recommended 3% branch / 5% total
  • Power factor is assumed at 0.85 for mixed motor and resistive loads in kVA to ampere conversions

Limitations

  • Does not perform a complete NEC Article 220 farm load calculation per NEC 220.103, which has specific farm building demand factors
  • Transformer sizing is approximate — actual specification requires consulting manufacturer impedance and temperature rise data
  • Does not account for harmonic loads from VFDs, LED lighting, or other non-linear loads that may require oversized neutrals
  • Ambient temperature correction factors for conductors in hot environments (above 30 degrees C) are not applied automatically
  • Does not model ground fault protection, arc flash calculations, or selective coordination of overcurrent devices
  • NEC edition differences may affect specific table values — this calculator references NEC 2020 as the baseline

References

  • NFPA 70 (NEC) Article 220 — Branch-Circuit, Feeder, and Service Load Calculations
  • NFPA 70 (NEC) Article 430 — Motors, Motor Circuits, and Controllers (FLA tables and feeder sizing)
  • NFPA 70 (NEC) Article 310 — Conductors for General Wiring (Table 310.16 ampacity)
  • NFPA 70 (NEC) Article 547 — Agricultural Buildings (special wiring requirements for farm structures)
  • Midwest Plan Service MWPS-28 — Farm Building Wiring Handbook
  • University of Missouri Extension — Farmstead Electrical Planning and Wiring Guide

Frequently Asked Questions

NEC demand factors account for the fact that not everything runs at full load simultaneously. General lighting gets first 10 kVA at 100%, remainder at 50%. Heating loads use the larger of 100% of the biggest heater or 65% of total connected heating. Oversizing wastes money on transformers and service equipment; undersizing trips breakers. Demand factors give you the realistic number.
Connected load is the sum of everything installed - all nameplate ratings added together. Demand load is what the NEC predicts will actually draw at any given time after applying demand factors. Demand load is always lower (often 40-60% of connected load) and is what you size the service to.
NEC 430.24 requires motor feeders to handle the starting current of the largest motor plus running current of all others. The 125% multiplier on the largest motor FLA approximates starting current requirements and prevents nuisance tripping during motor starts. This rule dominates the calculation on motor-heavy buildings like grain handling facilities.
Disclaimer: This calculator provides planning estimates based on NEC Article 220, 310, and 430. All electrical work must comply with the currently adopted edition of the NEC and local amendments. Consult a licensed electrician before installing or modifying electrical service equipment.

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