How do I size a service entrance conductor?

NEC 230.42: service conductor ampacity ≥ 100% of non-continuous + 125% of continuous. Size for calculated load per NEC 220. Minimum 100A residential service (NEC 230.79). Use aluminum SE cable to reduce cost.

What is the 125% continuous load rule?

NEC 210.20: overcurrent device and conductor rated ≥ 125% of continuous load (operating 3+ hours). For 20A continuous load: use 25A breaker and conductor rated ≥ 25A (AWG 10 copper at 30A).

When can I use aluminum conductors for residential wiring?

AWG 4 and larger: aluminum is acceptable and economical (75°C rating). AWG 6 aluminum for 40A cooktop circuits. AWG 12 aluminum for 15A branch circuits is now allowed with CO/ALR devices in NEC 2020.

NEC Wire Sizing Calculator

Size conductors per NEC 310 for branch circuits, feeders, and services. Account for continuous loads (125%), conduit fill derating, temperature correction, and voltage drop. Generate NEC-compliant wire schedule.

2D stress state at a point. All stresses in MPa.

σx — Normal Stress X (MPa)

σy — Normal Stress Y (MPa)

τxy — Shear Stress (MPa)

⚙ Mechanical Note: Results are based on standard textbook formulas and ISO/AASHTO references. Always verify critical designs with applicable codes (ISO 898, AASHTO 1993, AISC, Eurocode 3) and a qualified engineer.

How to Use

Enter the values for the patient or scenario you are assessing. Size conductors per NEC 310 for branch circuits, feeders, and services. Account for continuous loads (125%), conduit fill derating, temperature correction, and voltage drop. Generate NEC-compliant wire schedule. Use the nec wire sizing result to inform your clinical assessment.

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Frequently Asked Questions

How do I size a service entrance conductor?

What is the 125% continuous load rule?

When can I use aluminum conductors for residential wiring?