Canted coil spring contacts: how they work and how they are made

Spring contacts appear throughout daily life — in vehicles, electronic equipment and power connections. The structure is formed by welding the two ends of a spring wire together to make a ring. Because the finished part is small and unobtrusive, it is easy to ask what it is actually for. In the connector industry it is known as a spring contact, a canted coil spring or an inclined coil spring.

How the spring contact works

The wire coils are elliptical and skewed, so that when the ring is compressed each coil deforms independently while the spring as a whole reacts as a single unit. The load is therefore consistent at every contact point, and the spring maintains an almost constant elastic force over a large deflection range.

Because of these structural characteristics there are no real restrictions on how the contact is used. It suits both static and dynamic connections in medium- and high-voltage environments, works as a purely mechanical connection or as a path for high current, and is widely used in vehicles, electronic equipment, high-current connectors and high-voltage switchgear.

Why the design is economical and reliable

The spring contact is simple to manufacture, small and light, uses little material and is inexpensive — which makes it attractive for compact equipment where space is limited. The annular design provides multiple points of contact with a high contact force concentration and almost loss-free current transfer, giving a large current-carrying capacity and stable conductivity. Because the load is consistent across every contact point, the spring also wears evenly and lasts longer.

The same construction gives a wide working range, tolerates generous tolerances on the mating surface, and adapts well to machining and assembly error — all of which make the design well suited to large-scale production.

Material selection for spring contacts

Spring contacts supplied today are used mainly as electrical contacts in high-voltage switching. The most common materials are high-conductivity beryllium copper CuCo₂Be (C17500), high-strength beryllium copper CuBe₂ (C17200) and chromium zirconium copper CrZrCu (C18150).

Because the spring contact is not only a spring but also a conductor, high-conductivity beryllium copper is generally the best choice for coil spring fingers: it combines high strength, good conductivity and a high working temperature, and supports switchgear products in the 3.5 kV to 100 kV range.

Designing the contact angle

The skew angle α of the spring affects the contact stress. A larger α increases the resistance to deformation, while a smaller α reduces the deformation force. For dynamic connections, the spring should be lightly stressed while still ensuring full contact between the spring, the conductor and the guide sleeve. For static connections, a little more stress is acceptable because it further lowers the contact resistance.