Protection
Cable Sizing for Voltage Drop
Cable sizing starts from the required current-carrying capacity and from the maximum voltage drop the load can tolerate. The formula rearranges the resistance relationship to give the minimum cross-section for a chosen voltage-drop limit in a two-wire circuit. The result is a starting point: the final size must also satisfy the installation standard, the protective device, ambient derating and short-circuit withstand.
Cable Sizing for Voltage Drop
A = 2 × ρ × L × I ÷ ΔV_max
Variables and units
| Symbol | Quantity | Unit |
|---|---|---|
| A | Minimum conductor cross-section | m² |
| ρ | Conductor resistivity | Ω·m |
| L | One-way cable length | m |
| I | Load current | A |
| ΔV_max | Maximum permitted voltage drop | V |
Conditions of application
Voltage-drop-limited sizing for a two-wire DC circuit with equal go and return conductors. The result must then be checked against the conductor current-carrying capacity, derating factors, short-circuit withstand and local installation rules; the voltage-drop limit itself is installation- and application-specific.
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Educational cable-size estimate from current and voltage-drop limits.