Meaning
Electrical phenomena occurring at the interface of two conductors restrict the current to small areas of actual physical contact. This constriction resistance arises because surfaces are never perfectly smooth and touch only at the peaks of microscopic irregularities. The total ohmic loss at a terminal or busbar joint depends heavily on this effect.
Interface Topography
Microscopic peaks called asperities determine where the current flows between two mating parts. Because constriction resistance is inversely proportional to the number and size of these contact spots, surface finishing techniques significantly alter performance. High pressure forces these peaks to deform and increases the conductive path.
Rougher surfaces generally exhibit higher resistance due to the scarcity of contact points. Oxidation layers further impede flow by adding a resistive film to the narrow conduction channels.
Material Hardness
Softer metals allow for greater deformation and a larger contact area under a given clamping force. In the context of constriction resistance, the use of silver or tin plating reduces the hardness at the surface layer. This allows for lower resistance even when the base material is a harder alloy.
Power Loss
Heat generation at electrical joints stems from the localized voltage drop at the interface. High levels of constriction resistance lead to localized hot spots that can degrade insulation or cause thermal expansion. Terminal reliability over long periods relies on maintaining stable contact pressure to keep these losses low.
