2 A/mm² — the most conservative value, used for busbars inside enclosed switchgear with limited ventilation. Copper, ventilated enclosure: 1. A common rule‑of‑thumb for copper busbars: JCu≈1. 2≈1775 mm2 Select standard busbar size: A = 2 x 1000 = 2000 mm² (OK) A = 3 x 800 = 2400 mm² (More margin) Choose 2 × 100 × 10 mm² copper bars per phase (2000 mm². The Busbar Size Calculator helps engineers and electricians find the right copper or aluminum busbar dimensions based on current capacity, material type, and environmental conditions. This article explains how the calculator works, the standards it follows (IEC and NEC), and what factors influence. A busbar is a metal bar, usually made of copper or aluminum, that carries electricity inside switchgear. It connects the incoming power to circuit breakers and outgoing circuits, helping power flow smoothly and evenly. Good busbar design helps prevent overheating and electrical faults. In practical panel work, ETP copper C11000 is the standard choice because it balances conductivity, availability, fabrication ease, and cost. The material chosen, the mechanical constraints and the electrical performance for the specific application determine the conductor's minimum mechanical dimensions (see Conductor Size in the Electrical Design section).