[ I_t \ge \fracI_bC_t \times C_g \times C_i \times C_m ]
Proper cable sizing balances , efficiency , cost , and future expandability . 2. Key Factors Influencing Cable Size Before performing calculations, the following factors must be known: cable size calculation
| Factor | Description | |--------|-------------| | | The steady-state current drawn by the load (in Amperes). | | Cable length (L) | Longer cables require larger sizes to limit voltage drop. | | Voltage (V) | System voltage (e.g., 230V, 400V, 11kV). | | Phase | Single-phase or three-phase. | | Installation method | Buried directly, in conduit, on cable tray, clipped to surface, or in free air. | | Ambient temperature | Higher temperatures reduce current-carrying capacity. | | Grouping | Multiple cables together reduce heat dissipation. | | Insulation type | PVC, XLPE, EPR – each has different temperature ratings. | | Allowable voltage drop | Typically 2–5% of nominal voltage (e.g., 11.5V for 230V single-phase). | | Short-circuit withstand | The cable must survive fault currents until protection operates. | 3. Step-by-Step Cable Sizing Procedure Step 1: Calculate the Design Current (Ib) Single-phase: [ I_b = \fracPV \times \cos\phi ] [ I_t \ge \fracI_bC_t \times C_g \times C_i