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Electrical Calculator

Calculate wire gauge, circuit loads, and electrical material costs. NEC compliant calculations for safe electrical installations.

Electrical Calculations

Calculation Results

Wire Gauge 12 AWG
Breaker Size 20A
Conductor Type Copper
Voltage Drop 2.1%
Wire Cost/ft 0
Total Wire Cost $0

Common Wire Gauges

14 AWG: 15A circuits

12 AWG: 20A circuits

10 AWG: 30A circuits

8 AWG: 40A circuits

6 AWG: 55A circuits

NEC Requirements

  • 3% voltage drop max for branch circuits
  • 5% voltage drop max for feeders
  • 80% maximum circuit load
  • Grounding required for all circuits

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Electrical Calculator for Construction Projects

Accurate electrical calculations are crucial for safety and code compliance. Our free electrical calculator helps contractors and electricians determine proper wire sizing, circuit loads, and material costs according to National Electrical Code (NEC) requirements.

Wire Gauge Selection

Wire gauge (AWG) must be sized to handle the circuit amperage while maintaining acceptable voltage drop:

  • 14 AWG: 15 amp circuits (lighting, small outlets)
  • 12 AWG: 20 amp circuits (general outlets, small appliances)
  • 10 AWG: 30 amp circuits (dryers, water heaters)
  • 8 AWG: 40 amp circuits (ranges, larger appliances)
  • 6 AWG: 55 amp circuits (large equipment)

Voltage Drop Calculations

Voltage drop occurs when current flows through wire resistance. NEC limits voltage drop to:

  • 3% maximum for branch circuits (lighting and receptacles)
  • 5% maximum for feeders and service conductors
  • 8% maximum for ranges and dryers

Circuit Load Calculations

Circuit loads must be calculated to ensure breakers and wire are properly sized:

  • General lighting: 3 VA per square foot
  • Small appliance circuits: 1500 VA each
  • Laundry circuits: 1500 VA
  • Ranges: 8000 VA (or actual nameplate rating)
  • Dryers: 5500 VA (or actual nameplate rating)

Electrical FAQ

What wire gauge do I need?

Wire gauge is determined by the circuit amperage and conductor length. Use NEC tables for proper sizing. 12 AWG for 20A circuits, 10 AWG for 30A circuits, 8 AWG for 40A circuits. Longer runs require larger wire to prevent excessive voltage drop.

How do I calculate circuit load?

Calculate circuit load by adding the VA ratings of all devices on the circuit, then apply demand factors. General lighting loads are 3 VA/sq ft. Small appliance circuits are calculated at 1500 VA each. Never exceed 80% of the breaker rating for continuous loads.

What's the maximum voltage drop allowed?

NEC limits voltage drop to 3% for branch circuits (lights and outlets), 5% for feeders, and 8% for ranges and dryers. Excessive voltage drop can cause equipment malfunction and reduced lamp life. Always calculate voltage drop for long wire runs.

Do I need to ground all circuits?

Yes, grounding is required for all circuits in modern electrical systems. Ground wires provide a safe path for fault currents and help prevent electric shock. Use green or bare copper wire for grounding conductors, sized according to NEC Table 250.122.

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