Contact Arms for MV Switchgear

Arm, finger, contact — three different parts

Enquiries mix these up often enough to be worth separating, because they are quoted by different routes.

The contact arm is the structural conductor that links the operating mechanism to the contact face. It carries full breaker current and takes the mechanical load of opening and closing. It is a machined conductor, and its problems are current density, stiffness, and fatigue.

The contact finger is a spring-loaded element that maintains contact force in a plug-in or sliding joint. Its problems are spring rate and force retention — see bronze contact fingers and CuW contact fingers.

The contact itself is the mating face where current transfers, covered under contacts and contact assemblies.

Material and configuration

Material	Trade-off
Pure copper	Highest conductivity, heaviest, softest. The default where current dominates
Aluminum	Lighter and cheaper, lower conductivity, needs a larger section for the same current
Copper-aluminum bimetal	Copper where the joint and contact surfaces are, aluminum through the span. Used where weight and current both matter

Two supply configurations:

• Single contact arm — one arm at a time, for mechanisms using one arm per phase and for replacement orders where only one has failed
• Contact arm pair — two arms produced as a coordinated unit, same lot and geometrically aligned for the mechanism

Order the pair when the mechanism relies on the two arms tracking each other. Mixing a new arm with an aged one puts the contact timing out, and on a breaker that shows up as uneven contact wear rather than as an obvious fault. The contact arm selection guide covers the sizing route.

Common questions

Single or pair?

Pair if the two arms work as a coordinated unit in the mechanism, or if the existing pair has seen equal service. Single for one-per-phase designs and for a genuine one-off replacement.

Can you match an existing arm from a sample?

Yes. Send the sample and state the alloy if it is known. Mark the mounting interface and the contact face — those are the two surfaces where the tolerance actually matters, and a general tolerance note over the whole part costs money without buying anything.

What do you need to quote?

A drawing or sample, the material, continuous current rating, and quantity. If the arm is plated, state the plating and the masked areas.