Free Online Busbar Sizing Calculator

Busbars carry the full switchboard current and must run without overheating or excessive voltage drop. This calculator sizes copper or aluminium busbars from the design current, using the standard current density and cross-section approach of IS 8084 / IEC 61439.

Busbars are rated by current density - roughly 1.2-1.6 A/mm² for copper and 0.8-1.0 A/mm² for aluminium in still air - derated for temperature rise, enclosure and grouping. Copper carries about 1.5 times the current of the same aluminium section but costs more; large distribution boards often use aluminium risers with copper for final connections.

Example: A 1600 A copper busbar at a current density of 1.4 A/mm² needs a cross-section of 1600 / 1.4 ≈ 1143 mm² - met by two 100 × 6 mm bars per phase (1200 mm²). The same duty in aluminium at 0.9 A/mm² needs about 1778 mm², so a larger bar section. Both must also pass the short-circuit withstand check.

Indicative continuous ratings for single bars in air (derate inside enclosures):

Derating & Short-Circuit

Ratings fall inside enclosures (poor ventilation), at high ambient temperature and when bars are grouped closely. Beyond the continuous rating, busbars must survive the fault current for the protection's clearing time without deforming - the short-circuit (I²t) withstand check often governs the bracing and support spacing more than the continuous rating.

Indicative in-air values - confirm against IS 8084 tables and the switchboard type-test data.