Connector Contact Resistance

Formula

Description

When two conductors are pressed together, they make contact only at small asperity points rather than across the entire apparent contact area. The constriction resistance at each contact spot depends on the material resistivity and the effective contact radius. Higher contact force increases the contact area by plastic deformation of asperities, reducing resistance. This model explains why connector contact resistance depends strongly on contact force, surface finish, and contamination. Gold plating is used on connectors not because gold is a better conductor but because it resists oxidation, maintaining clean metal-to-metal contact.

Variables

• Rc — Constriction resistance at one contact spot (Ω)
• ρ — Resistivity of the contact material (Ω·m)
• a — Effective radius of the contact spot (m)

Practical Notes

Typical connector contact resistance: gold-plated 1-10 mΩ, tin-plated 2-50 mΩ, bare copper 5-100 mΩ (varies with age and environment). Contact resistance increases over time due to oxidation and fretting corrosion. Specify gold plating (0.75 µm minimum) for signal contacts with low insertion cycles, and harder gold (gold-cobalt alloy) for contacts that are frequently mated.