How do I determine the correct conductor cross-section for cables in a domestic electrical upgrade?

Cable sizing depends on the expected load current, maximum permissible voltage drop, and the installation method, which affects heat dissipation. As a general rule under IEC 60364-5-52, lighting circuits typically require a minimum of 1.5 mm² copper conductors, while socket outlet circuits need at least 2.5 mm², but these sizes may need to be increased for long cable runs or when cables are bunched or installed in thermal insulation. The protective device rating and the maximum earth fault loop impedance must also be considered to ensure automatic disconnection under fault conditions, so always refer to your national wiring regulations for precise selection.