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Tool: Wire Gauge Calculator — Безкоштовний Онлайн Калькулятор | HomeCalcPro | Дата друку:
Wire Gauge Calculator — Безкоштовний Онлайн Калькулятор | HomeCalcPro
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National Electrical Code (NEC) Voltage Drop Formula
Transparent mathematical methodology explained in plain English.
Voltage Drop V = 2 × Distance (ft) × Current (Amps) × Resistance (Ohms/1,000 ft) / 1,000 | Drop % = (V_drop / Voltage) × 100National Electrical Code (NEC Article 210.19) recommends sizing electrical conductors so voltage drop does not exceed 3% on branch circuits (5% total including feeder).
Variables Explained:
- Circuit Voltage (V): 120V AC (Standard), 240V AC (Appliance/Subpanel), 12V DC, or 48V DC.
- Circuit Current (Amps): Maximum expected continuous load in Amperes.
- One-Way Distance (ft): Distance from breaker panel to load.
- Conductor Material: Copper or Aluminum.
20 Amp Load on a 120V AC Circuit Running 85 Feet (Copper Wire)
Selecting optimal wire gauge to stay under NEC 3% voltage drop.
- Test 12 AWG (Resistance = 1.93 Ω/1,000 ft): (2 × 85 × 20 × 1.93) / 1,000 = 6.56 Volts drop (5.47% drop - Fails 3% limit).
- Test 10 AWG (Resistance = 1.21 Ω/1,000 ft): (2 × 85 × 20 × 1.21) / 1,000 = 4.11 Volts drop (3.43% drop - Borderline).
- Test 8 AWG (Resistance = 0.764 Ω/1,000 ft): (2 × 85 × 20 × 0.764) / 1,000 = 2.60 Volts drop (2.17% drop - Passes NEC <3%).
Поширені Запитання (FAQ): Wire Gauge Calculator
Click any question below to expand quick answers, formulas, and expert tips.
What happens if wire gauge is too thin over long distances?
Under-sized wire causes excessive heat buildup (fire hazard) and voltage drop, which starves motors, power tools, and appliances of power, causing premature motor burnout.
What is the maximum allowed voltage drop under the National Electrical Code?
NEC recommends a maximum 3% voltage drop for any branch circuit, and a maximum 5% total voltage drop for feeder plus branch circuits combined.