Electrical
Cable Sizing Calculator
Estimate cable size from design current using standard current-carrying capacities.
Use this calculator for preliminary cable sizing checks based on design current and tabulated current-carrying capacities. It is intended as an early-stage estimating tool only and should be checked against the full installation method, correction factors and project requirements.
Inputs
The combined rating factor should include any applicable ambient temperature, grouping, thermal insulation or other derating factors.
Result
Method
Required tabulated current-carrying capacity is estimated by applying the combined rating factor:
The selected cable size is the smallest size with tabulated current-carrying capacity equal to or greater than the required value.
- Ib = design current (A)
- C = combined rating factor
- It = required tabulated current-carrying capacity (A)
- The smallest listed cable size with sufficient tabulated capacity is selected.
- Calculated result = -
Reference
- This calculator provides a preliminary cable size selection based on design current and tabulated current-carrying capacities.
- Current-carrying capacities vary depending on cable type, insulation type, conductor material and installation method.
- Relevant standards and guidance may include BS 7671 and associated tabulated current-carrying capacity data.
- Final cable sizing should also consider voltage drop, earth fault loop impedance, disconnection time, short-circuit withstand and installation conditions.