Because aluminium expands and contracts, flat washers are useless in hot environments.
If a system must run hot (e.g., 90-100°C continuous), the INDAL Handbook recommends:
When ambient temperatures exceed 40°C, the busbar must be derated. The INDAL formula is: [ I_rated = I_base \times \sqrt\fracT_max - T_amb_hotT_max - T_amb_base ] indal handbook for aluminium busbar hot
For example, a busbar rated for 1000A at 35°C must be reduced to ~800A when the ambient temperature hits 65°C (common in outdoor metal-clad switchgear in summer).
For a 100mm x 10mm busbar, AC current crowds to the surface. Because aluminium expands and contracts, flat washers are
Unlike copper, aluminium has a higher coefficient of thermal expansion (23.8 x 10⁻⁶ /°C vs. copper’s 16.8 x 10⁻⁶ /°C) and different creep characteristics. When a busbar gets "hot" (operating at 85°C to 105°C), three things happen:
The INDAL handbook historically addressed these issues not as failures, but as design parameters. A "hot" busbar is acceptable provided the system is designed for it. The INDAL handbook historically addressed these issues not
Hot busbars need breathing room. The INDAL handbook mandates: