What Cable Size Do I Need for My Load Current?

Continuous Current Capacity

Start with the design current and an ampacity method accepted by the project. Cable tables assume defined installation and temperature conditions. Correction factors are applied when the real conditions differ.

Grouped loaded cables, thermal insulation, high ambient temperature and poor soil heat dissipation can significantly reduce capacity.

Voltage Drop

Long routes can require a larger conductor even when thermal ampacity is adequate. Check steady-state drop and, for motors, starting performance. Power factor and conductor reactance can matter on larger AC circuits.

Fault and Protection Checks

The conductor and protective conductor must withstand the expected fault energy until the protective device clears it. The device must also disconnect within the required time and protect the cable against overload.

Data Needed for a Calculation

• Load current and load type
• Voltage, phase and frequency
• One-way route length
• Installation method and ambient conditions
• Number of grouped circuits
• Fault level, clearing time and voltage-drop limit