Voltage Drop Calculator

Calculate voltage drop in electrical circuits to ensure proper wire sizing and electrical code compliance.

Calculate Voltage Drop

What is Voltage Drop?

Voltage drop is the decrease in electrical potential along the path of a current flowing in an electrical circuit. Excessive voltage drop can lead to inefficient operation of electrical equipment and potential safety hazards.

Why Calculate Voltage Drop?

The National Electrical Code (NEC) recommends that voltage drop should not exceed:

  • 3% for branch circuits
  • 5% for combined feeder and branch circuits

Calculating voltage drop helps ensure your electrical system operates efficiently and safely while complying with electrical codes.

Voltage Drop Formula

The voltage drop formula varies based on the circuit type:

Single Phase: VD = 2 × I × R × L

Three Phase: VD = √3 × I × R × L

Where: VD = Voltage Drop, I = Current (Amps), R = Resistance (Ohms/foot), L = Length (feet)

Factors Affecting Voltage Drop

  • Wire Gauge (AWG): Larger wire gauges have lower resistance
  • Wire Length: Longer wires increase voltage drop
  • Current Load: Higher current increases voltage drop
  • Wire Material: Copper has lower resistance than aluminum
  • Temperature: Higher temperatures increase resistance

How to Reduce Voltage Drop

  1. Use larger wire gauge (lower AWG number)
  2. Minimize wire run length when possible
  3. Use copper wire instead of aluminum
  4. Consider increasing circuit voltage (e.g., 240V vs 120V)
  5. Split loads across multiple circuits

Common Applications

Voltage drop calculations are essential for:

  • Long wire runs in large buildings
  • Solar panel installations
  • EV charging station wiring
  • Outdoor lighting circuits
  • Sub-panel installations
  • Motor and HVAC equipment circuits