Copper busbars are used within the HV industry and in battery packs.
The red circles show data from 5 electric vehicle battery busbars. The current is an estimated continuous rating and plotted versus the cross-sectional area in mm2.
The gradient of the “straight line fit” shows that 5.9A/mm2 is a rough estimate for copper busbar size. However, to be on the safe side of this I would initially size at 5A/mm2 before doing the detailed electrothermal analysis.
Copper surface corrosion is an important subject when considering copper busbar joints. When copper is exposed to air and moisture, it forms a thin layer of reddish-brown copper oxide and other corrosion products. These products are not as conductive as the copper, leading to increased resistance at the joint.
The increased resistance leads to local heating at the joint and faster corrosion, this is described by Stäubli’s study on long-term behaviour of bare, bolted busbar joints:
Progressive film build-up increases the joint resistance Rv, heat losses and therefore the temperature of the joint, which in turn accelerates the chemical reaction producing the film build-up. This “vicious circle” of film build-up, heat loss and joint temperature can ultimately cause the busbar joint to fail totally as a result of overheating.
See also: Busbar Fasteners, Photo Etching, Aluminium Busbar, Continuous Current Rating