): For long runs, the resistance of the wire causes voltage to drop before reaching the device. Ensure the drop is of the rated voltage. Formula: (for 3-phase).

Cables bunched together generate more collective heat.

| 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. |

Leads to excessive heat, which degrades insulation and can cause electrical fires . It also results in a high voltage drop , which can cause motors to burn out or electronics to malfunction.

Once the design current is established, the next critical factor is the installation method. A cable’s ability to dissipate heat varies dramatically depending on its environment. A cable installed in open air can shed heat easily, whereas a cable buried underground or enclosed in a wall cavity retains heat. To account for this, engineers apply correction factors (derating factors). For instance, if multiple cables are bunched together in a single tray, the heat from one cable affects its neighbors, requiring a reduction in the cable's current-carrying capacity. Environmental conditions, such as ambient temperature and soil thermal resistivity, further influence these correction factors.