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Calculate voltage drop on wire runs for NEC compliance. Enter wire size, length, amperage, and voltage to find drop percent and minimum wire size.
Size circuit breaker from wire gauge and load type. Match overcurrent protection to conductor ampacity per NEC 240.4 for residential circuits.
Calculate conduit fill percentage per NEC Chapter 9. Enter conduit size, wire gauge, and conductor count to verify fill limits for EMT, PVC, and rigid conduit.
Continuous loads (3+ hours) limited to 80% of breaker rating per NEC 210.19(A).
Ib = Load Watts ÷ Voltage; or use breaker rating × 80% for continuous loadsSelect wire from NEC Table 310.16 with ampacity meeting or exceeding required value.
Required Ampacity ≥ Load Current ÷ 0.80 (continuous) or ≥ Load CurrentHigher temperature rating (75°C, 90°C) allows higher ampacity if terminations rated accordingly.
14 AWG = 15A; 12 AWG = 20A; 10 AWG = 30A (60°C copper, typical)Updated: July 2026
20A breaker requires minimum 12 AWG copper at 60°C (20A ampacity). 14 AWG insufficient.
30A load needs 10 AWG copper (30A at 60°C). Verify 4-wire NEMA 14-30 outlet.
21A continuous → 26.25A required ampacity → 10 AWG on 30A breaker.
Determine minimum AWG conductor size for a circuit based on load current, conductor material, and insulation temperature rating. Enter amperage, single or multi-conductor, and ambient conditions for NEC Table 310 ampacity-based wire selection.