Battery Cable Size Calculator

Determine the optimal cable size for your DC electrical system to minimize voltage drop.

Battery Cable Size Calculator

Compliant with NEC Standards (General Guide)

Results:

Max Allowed Voltage Drop (V): 0.00

Required Cable Resistance (Ohms/1000ft): 0.00

Suggested Cable Size: Consult Tables

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How to Use the Calculator

Input Battery Voltage

  1. Enter the nominal voltage of your battery bank (e.g., 12V, 24V, 48V).
  2. This is crucial for accurate voltage drop calculations.

Input Current (Amps)

  1. Enter the maximum continuous current (Amps) that will flow through the cable.
  2. Consider peak loads for safety and performance.

Input Cable Length & Max Voltage Drop

  1. Enter the one-way length of the cable run in feet.
  2. Specify the maximum acceptable voltage drop percentage (e.g., 3% for critical loads).

Battery Cable Sizing Fundamentals

Voltage Drop

Voltage drop is the reduction in electrical potential along a conductor due to its resistance. Excessive voltage drop can lead to:

  • Reduced efficiency of appliances
  • Overheating of cables
  • Premature battery wear

Current Capacity & Temperature

  • Cables must be sized to safely carry the maximum current without overheating.
  • Higher temperatures reduce a cable's current carrying capacity (ampacity).
  • Always consult NEC or local electrical codes for specific ampacity ratings and temperature correction factors.

Key Formulas:

Voltage Drop (Vd) = (2 × L × I × R) / 1000

Required Resistance (R_req) = (V × %Drop / 100) / (2 × L × I) × 1000

Calculation Formulas

Max Allowed Voltage Drop (Vd_max):
Vd_max = V_battery × (%Drop / 100)

Total Circuit Length (L_total):
L_total = 2 × Cable_Length (one way)

Required Cable Resistance (Ohms/1000ft):
R_req = (Vd_max / (I × L_total)) × 1000

Example Calculation

12V Battery System:

Battery Voltage: 12V

Current: 50A

Cable Length (one way): 20ft

Max Voltage Drop: 3%

Vd_max = 12V × (3 / 100) = 0.36V

L_total = 2 × 20ft = 40ft

R_req = (0.36V / (50A × 40ft)) × 1000 = 0.18 Ohms/1000ft

Result: Max Allowed Voltage Drop = 0.36V | Required Resistance = 0.18 Ohms/1000ft

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