Wire Gauge Selection Guide

Everything you need to know about choosing the correct wire gauge for safe and efficient electrical installations.

Quick Start: 3-Step Wire Selection

1

Calculate Total Amperage

Add up all device currents on the circuit, include 125% safety margin for continuous loads

2

Measure Wire Run Length

Measure total distance from power source to load (include return path)

3

Use Our Calculator

Enter your values in our wire gauge calculator for instant recommendations

Understanding AWG System

The American Wire Gauge (AWG) system uses inverse numbering: smaller numbers = larger wires = higher capacity.

Common Applications:

  • AWG 14 - 15A circuits, lighting (2400W @ 120V)
  • AWG 12 - 20A circuits, outlets (2400W @ 120V)
  • AWG 10 - 30A circuits, AC units (3600W @ 120V)
  • AWG 8 - 40-50A, electric ranges
  • AWG 6 - 55-65A, EV chargers, sub-panels

Voltage Drop Considerations

Voltage drop is the reduction in voltage along a wire due to resistance. NEC recommends ≤3% drop for branch circuits, ≤5% total.

Why It Matters:

  • Excessive drop causes motors to overheat
  • Lights dim, especially during startups
  • Reduced efficiency and wasted energy
  • Shortened equipment lifespan

Solution:

Use larger wire gauge for long runs (>50ft requires special attention)

Ampacity & Temperature Ratings

Ampacity is the maximum current a wire can safely carry without overheating based on its insulation rating.

Insulation Types:

  • 60°C (TW, UF)
    Older standard, wet locations
  • 75°C (THWN, THHN)
    Most common, dry/wet locations
  • 90°C (THHN, XHHW)
    High temp, dry locations only

Copper vs Aluminum Wire

✓ Copper Advantages:

  • Lower resistance
  • More flexible
  • Better conductivity
  • Smaller gauge needed
  • Residential standard

✓ Aluminum Advantages:

  • Lower cost
  • Lighter weight
  • Good for long runs
  • Service entrance
  • Large feeders

Note: Aluminum requires 2 gauge sizes larger than copper for same ampacity

Common Wire Sizing Mistakes to Avoid

❌ Don't:

  • Ignore voltage drop on long runs
  • Use undersized wire to save money
  • Forget the 80% continuous load rule
  • Mix copper and aluminum without proper connectors
  • Exceed breaker size ratings

✓ Do:

  • Calculate based on actual load + safety margin
  • Consider future expansion needs
  • Follow NEC Table 310.16 for ampacity
  • Use our calculator for accurate sizing
  • Consult electrician for complex installations

Real-World Example: Sizing Wire for a Workshop

Scenario:

Installing a 240V, 30A circuit for a workshop 100 feet from the main panel.

Step 1: Check NEC Ampacity Table

AWG 10 copper is rated for 30A at 60°C (NEC 310.16)

Step 2: Calculate Voltage Drop

AWG 10 resistance: 1.0Ω/1000ft
Drop = (1.0 × 200ft × 30A) / 1000 = 6V
Percentage = (6V / 240V) × 100 = 2.5% ✓ (Under 3% limit)

Result: AWG 10 Copper Wire

Meets both ampacity and voltage drop requirements. Use THHN/THWN-2 insulation rated for 90°C.

Ready to Size Your Wire?

Use our free calculator to get instant wire gauge recommendations for your project.

Wire Gauge CalculatorView AWG Chart