Busbar Sizing Calculator
Compare a continuous-current density screen with an adiabatic short-circuit minimum and identify the governing preliminary cross-section.
Calculation method
The continuous-current screen divides design current by the entered current density. The short-circuit screen applies the adiabatic relation S = I√t / k. The calculator takes the larger cross-section and finds the first rectangular bar in its simple geometric list with at least that area.
How to use the result
Use the result to establish a preliminary copper or aluminium cross-section and to see whether continuous current or short-circuit thermal stress is governing. The suggested bar dimension is geometric only; it is not a certified ampacity and should not be treated as an IEC 61439 temperature-rise verification.
Engineering limits
Busbar ampacity depends on enclosure, orientation, number of bars per phase, spacing, ventilation, ambient temperature, joints, plating, emissivity, proximity and permissible temperature rise. Electrodynamic short-circuit forces and support spacing are also separate checks. Verify the final assembly by the applicable design-verification method and manufacturer data.
Before design release
Record the source and revision of every project input used in this calculation, then compare the result with the next practical equipment or conductor size rather than treating the numerical minimum as an automatic selection. Check tolerances, environmental derating, duty cycle, protection settings, installation constraints and manufacturer limits that are outside the simplified model. Where the result feeds another study, carry the same voltage, current, power-factor, fault-level and timing assumptions forward so the design chain remains traceable. Save the governing case and the reason for the final engineering choice. ElectroDesigner is intended to make the calculation path visible; it does not replace the project engineer’s verification, the adopted standard or tested manufacturer data.