n China, medium- and low-voltage switchgear rarely uses aluminum busbars. Copper remains the dominant choice. For many engineers and customers, the very mention of aluminum evokes suspicion — a reflexive association with cost-cutting and compromised quality. Yet, the reality is far more nuanced. When designed, treated, and installed correctly, aluminum busbars can perform reliably, safely, and economically.

Why Aluminum Busbars Are Often Misunderstood

Aluminum’s reputation problem largely stems from its tendency to oxidize. When exposed to air, its surface rapidly forms a thin layer of aluminum oxide — a compound that is almost an electrical insulator. This oxide film increases contact resistance, and if joint surfaces are not properly prepared, localized overheating can occur.

However, oxidation is not an unsolvable issue. Modern engineering techniques easily mitigate it. For example, tin-plating aluminum busbars effectively prevents oxidation and maintains a stable, low-resistance interface over long-term operation. Alternatively, the oxide layer can be mechanically removed before assembly, followed by the application of appropriate jointing compounds and ensuring proper bolt torque. When executed correctly, such methods can make the contact interface nearly as reliable as that of copper.

Why Some Markets Prefer Aluminum

While aluminum busbars face skepticism domestically, international markets—such as India—show a strong preference for them. During a collaborative design project for Indian low-voltage switchgear, several valuable insights emerged. Aluminum’s lower cost, lighter weight, and adequate conductivity make it a pragmatic choice for large-scale distribution systems, especially where cost efficiency is a major consideration.

In these systems, proper surface treatment, joint design, and thermal management allow aluminum to deliver performance well within safety and reliability thresholds. The key lies not in the material itself, but in understanding and compensating for its characteristics.

Determining Aluminum Busbar Current-Carrying Capacity

The current-carrying capacity of aluminum busbars can be referenced from DIN 43670, a German standard widely adopted in electrical design. For example, a 100 mm × 10 mm bare aluminum busbar has a rated current of 1190 A under the following conditions:

• Ambient temperature: 35°C

• Maximum operating temperature: 65°C

• Temperature rise (ΔT): 30 K

This baseline value provides a reference, but real-world applications often deviate from standard conditions. A busbar’s current-carrying capacity directly depends on the permissible temperature rise — the difference between its operating and ambient temperatures.

Temperature Rise and Correction Factors

Ignoring ambient and operating temperatures when discussing current capacity is meaningless. The temperature rise, expressed in Kelvin (K), is a critical determinant. DIN 43670 includes correction factors for different temperature scenarios.

For instance, if the ambient temperature increases to 40°C and the permissible operating temperature rises to 90°C, the temperature rise becomes 50 K. The standard’s correction factor for this condition is 1.32. Therefore, the corrected current-carrying capacity is:

$$I_{new} = 1190 \times 1.32 \approx 1571\,A$$Inew=1190×1.32≈1571A

This illustrates how even small variations in thermal conditions can significantly influence the permissible current.

Mathematical Relationship Between Temperature and Current

The correlation between current capacity and temperature rise is nonlinear. As temperature increases, resistivity rises, leading to additional losses and heat generation. The relationship can be approximated by empirical or analytical models that relate thermal dissipation, conductor cross-sectional area, and material resistivity.

If the allowable operating temperature is fixed, one can calculate the permissible current at different ambient conditions by adjusting the temperature rise and applying corresponding correction factors. Simulation tools can further refine these estimates by considering heat dissipation through conduction, convection, and radiation.

Practical Case: Aluminum Busbar Design in Indian Switchgear

In the previously mentioned low-voltage cabinet project, the system design assumed:

• Maximum operating temperature: 90°C

• Ambient temperature: 40°C

• Derating requirement at 50°C ambient

Under these conditions, theoretical calculations began with DIN 43670 data and were then validated through simulation and physical testing. The final design incorporated adequate safety margins, ensuring stable operation even under high-load and high-temperature environments.

This case demonstrated that with proper design methodology, aluminum busbars can fully meet demanding performance requirements while offering considerable material and weight savings.

Conclusion

Aluminum busbars, when properly engineered, are not a compromise but a calculated choice. Their performance depends on precise thermal analysis, surface treatment, and mechanical integrity rather than on the intrinsic limitations of the metal itself.

By applying standards such as DIN 43670, adjusting for real-world conditions, and conducting empirical validation, engineers can design aluminum busbar systems that are both reliable and cost-effective. In an industry increasingly focused on efficiency and sustainability, it may be time to reexamine long-held prejudices — and recognize aluminum for the capable conductor it truly is.