35 mm, 16 mm, and 25 mm cables are common conductor sizes used in low‑voltage and medium‑voltage electrical installations. The cross‑sectional area, measured in square millimetres (mm²), determines the current‑carrying capacity, voltage drop characteristics, and mechanical strength of the cable. Selecting the correct size is essential for safety, efficiency, and long‑term reliability of the electrical system.A 16 mm cable is typically used for small to medium power distribution, such as feeder lines for residential or light commercial installations, connection between distribution boards, and shorter runs to smaller loads. It offers a good balance between flexibility and ampacity, making it suitable for circuits that do not demand very high current. Because of its relatively smaller diameter, it is easier to install in conduits and cable trays with limited space. It is frequently found in lighting panels, small motor supplies, and general‑purpose power circuits where the design current and voltage drop requirements can be met with this size.A 25 mm cable is often used where higher current is required, for example as a main supply cable in small buildings, connection to larger single‑phase or three‑phase loads, and as a sub‑main between major distribution boards. It provides greater current‑carrying capacity than 16 mm while still maintaining reasonable flexibility for installation. This size is commonly selected when the cable run is longer, and voltage drop must be kept within specified limits. It can be used to supply equipment such as larger motors, heating equipment, and small distribution transformers, depending on installation conditions, insulation type, and permissible temperature rise.The 35 mm cable is intended for even higher current applications. It is typically used as a main feeder in commercial or light industrial systems, as well as for connections to high‑demand equipment. This size is suitable for longer runs where both current rating and voltage drop are critical design factors. The larger cross‑section reduces electrical resistance, improving efficiency and limiting energy loss in the form of heat. However, with the increased conductor size comes greater overall diameter and weight, so bending radius, support spacing, and installation methods must be carefully considered during design.All three sizes can be manufactured in copper or aluminium, with various insulation materials such as PVC, XLPE, or rubber compounds, and in single‑core or multi‑core configurations. The choice among 16 mm, 25 mm, and 35 mm must always be based on detailed calculations that consider installation method, ambient temperature, grouping of cables, fault current withstand capability, and applicable electrical standards. Proper selection helps ensure that the cable operates safely, minimises energy loss, and delivers stable power to connected equipment throughout its service life.