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NEC Article 215.2(A)(1) Informational Note 2Worked ExampleElectrical

Subpanel Feeder Voltage Drop Calculation: 250ft 6 AWG at 50A 240V

Calculate feeder voltage drop over 250 feet for a 50A 240V subpanel using 6 AWG copper under NEC 215.2 recommendations.

Direct Answer
12.29 V Drop (5.12% Loss - Upsize to 4 AWG Copper)

Calculated strictly in accordance with NEC Article 215.2(A)(1) Informational Note 2.

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Given Scenario Parameters

distance250
wire Gauge6 AWG
current50
voltage240
phase1

Interactive Calculator (Pre-filled)

Adjust inputs to evaluate variations of this NEC code scenario.

Circuit Parameters & Electrical Load

Calculate wire gauge, voltage drop, and NEC 310.16 ampacity for single-phase, 3-phase, and DC circuits.

Circuit System:
AC Presets:
Standard Breaker Sizes:
Verified NEC Code Proof Available (NEC 215.2(A)(1) & NEC 310.16)Configuration matches: 250ft 6 AWG at 50A 240V Subpanel Feeder Proof
Inspect Code Proof

Recommended Conductor & Voltage Drop Sizing

240V • 50A Load • 250 ft run
Recommended Minimum Conductor Size (COPPER):
3 AWGCOPPER (52,620 CM)

Delivers 233.87V at load terminal with 2.55% voltage drop (-6.13V drop).

Actual Voltage Drop6.13V (2.55%)
Voltage at Load233.87V delivered
NEC Base Ampacity100A (100A derated)
Max 3% Distance293.7 ft limit
Copper vs. Aluminum Conductor ComparisonAt 250 ft run
Copper (Cu) Recommendation3 AWG
2.55% DropHigher conductivity
Aluminum (Al) Recommendation1 AWG
2.64% DropLower material weight/cost
Educational and reference calculator only. Conductor sizing must comply with the National Electrical Code (NEC Table 310.16), local AHJ amendments, equipment terminal temperature ratings (60°C/75°C), and short-circuit withstand ratings. Always consult a licensed electrical contractor.
Target ≤ 3% • K = 12.9 Ω·cmil/ft

Circuit Voltage Drop & Conductor Schematic

PASS (< 3%)Single-Phase AC
SOURCE240VMain Panel50ALOAD233.87VEquipment / SubDelivered250 ft One-Way Run (500 ft Loop)3 AWG COPPERΔV = -6.13V (2.55% drop)
Conductor Size3 AWG (copper)
Voltage at Load233.87 Volts (-6.13V)
Voltage Drop %2.55% (Target ≤ 3%)
Max Distance (3%)293.7 ft limit

Conductor Candidate Sizing & Voltage Drop Comparison Table

COPPER Conductors
Conductor SizeCircular MilsBase / Derated AmpacityVoltage DropVoltage at LoadMax 3% DistanceStatus
14 AWG4,110 CM20A / 20A78.47V (32.7%)161.53V22.9 ftFAIL
12 AWG6,530 CM25A / 25A49.39V (20.58%)190.61V36.4 ftFAIL
10 AWG10,380 CM35A / 35A31.07V (12.95%)208.93V57.9 ftFAIL
8 AWG16,510 CM50A / 50A19.53V (8.14%)220.47V92.1 ftFAIL
6 AWG26,240 CM65A / 65A12.29V (5.12%)227.71V146.5 ftFAIL
4 AWG41,740 CM85A / 85A7.73V (3.22%)232.27V233 ftWARNING
3 AWGRecommended52,620 CM100A / 100A6.13V (2.55%)233.87V293.7 ftRECOMMENDED
2 AWG66,360 CM115A / 115A4.86V (2.03%)235.14V370.4 ftPASS
1 AWG83,690 CM130A / 130A3.85V (1.6%)236.15V467.1 ftPASS
1/0 AWG105,600 CM150A / 150A3.05V (1.27%)236.95V589.4 ftPASS
2/0 AWG133,100 CM175A / 175A2.42V (1.01%)237.58V742.9 ftPASS
3/0 AWG167,800 CM200A / 200A1.92V (0.8%)238.08V936.6 ftPASS
4/0 AWG211,600 CM230A / 230A1.52V (0.63%)238.48V1181 ftPASS
250 kcmil250,000 CM255A / 255A1.29V (0.54%)238.71V1395.3 ftPASS
300 kcmil300,000 CM285A / 285A1.08V (0.45%)238.92V1674.4 ftPASS
350 kcmil350,000 CM310A / 310A0.92V (0.38%)239.08V1953.5 ftPASS
400 kcmil400,000 CM335A / 335A0.81V (0.34%)239.19V2232.6 ftPASS
500 kcmil500,000 CM380A / 380A0.65V (0.27%)239.35V2790.7 ftPASS
600 kcmil600,000 CM420A / 420A0.54V (0.23%)239.46V3348.8 ftPASS
750 kcmil750,000 CM475A / 475A0.43V (0.18%)239.57V4186 ftPASS
1000 kcmil1,000,000 CM545A / 545A0.32V (0.13%)239.68V5581.4 ftPASS
NEC Electrical Code & Safety Disclaimer: This calculation is for design and reference estimation only. Final conductor sizing must comply with the National Electrical Code (NEC Article 310, Table 310.16), local electrical amendments, terminal temperature ratings (typically 75°C), and equipment manufacturer specifications. High-voltage and feeder installations should be verified by a licensed electrical contractor.

Calculation Methodology & Mathematical Steps

1.Calculate Voltage Drop for Recommended 3 AWG (COPPER): (2.0 × 12.9 × 50A × 250 ft) ÷ 52620 CM
= 6.13V (2.55% drop, 233.87V at load)
2.Determine Maximum Distance for 3% Voltage Drop: (0.03 × 240V × 52620) ÷ (2.0 × 12.9 × 50A)
= 293.7 ft maximum one-way length

Step-by-Step Solution

Formal engineering derivation citing applicable National Electrical Code articles.

Governing Code Equation
VD = (2 * K * L * I) / CM
Citing NEC Article 215.2(A)(1) Informational Note 2
1

Identify circular mil area for 6 AWG copper (CM = 26,240) and resistivity constant (K = 12.9 ohms-cmil/ft).

2

Compute feeder voltage drop: (2 * 12.9 * 250 * 50) / 26,240 = 12.29 Volts.

3

Determine percentage drop: (12.29 / 240) * 100 = 5.12%.

4

Compare with NEC recommendation: 5.12% exceeds the recommended 3% maximum. Upsize conductor to 4 AWG copper to keep drop below 3% (7.73V / 3.22%).

Conclusion: 12.29 V Drop (5.12% Loss - Upsize to 4 AWG Copper)
NEC Article 215.2(A)(1) Informational Note 2