Contact Arms for MV Breakers: Single vs Pair, and Material Selection
Contact arms connect the operating mechanism in an MV breaker to the contact face. They carry full breaker current, support the mechanical motion of opening and closing, and in many designs are the visible moving element when the breaker actuates. Two choices drive contact arm sourcing: single vs paired configuration, and material. This guide covers both.
For the products, see Contact Arms.
Single vs Paired
The configuration is set by the breaker mechanism design:
- Contact Arm Single: one arm per phase. Common in compact MV breakers (distribution-class 12 kV) and for replacing one side of a worn assembly.
- Contact Arm Pair: two arms working as a coordinated unit, supplied as a matched set from the same material lot. For larger breakers with dual-path current systems, and for new builds where dimensional consistency between the two arms matters.
When to order which: single-arm mechanism, or replacing one side → single. Dual-arm mechanism, or new build needing matched consistency → pair.
Material Selection
Contact arm material trades conductivity against weight and mechanical duty:
| Material | When to use |
|---|---|
| ETP copper C11000 | Standard MV breaker duty; maximum conductivity |
| Aluminum (6061-T6) | Weight-sensitive designs; cost-optimized, size up cross-section for lower conductivity |
| Copper-aluminum bimetal | Compromise: aluminum's weight savings with copper conductivity at the contact face |
| Aluminum bronze C95400 | High-fatigue mechanical duty |
Copper is the default. Aluminum and bimetal appear in weight-sensitive or cost-driven designs. Aluminum bronze shows up where the arm sees high mechanical fatigue.
Arc-Resistant Tips
Contact arms that see arc duty at the contact face can have a CuW tip brazed on, copper arm for the current path and mechanical structure, CuW tip for arc resistance. Specify both the arm drawing and the CuW geometry; we braze and supply the complete assembly.
Plating
The contact zones (where the arm mates with adjacent conductors) are typically silver-plated for low-resistance joints. The bulk of the arm is bright-machined. Specify plating zones in your drawing.
Selection Path
- Single-arm mechanism or one-side replacement? → Contact Arm Single
- Dual-arm mechanism or new matched build? → Contact Arm Pair
- Material: copper (default) / aluminum (weight) / bimetal (compromise) / aluminum bronze (fatigue)
- Arc duty at the face? → add a pre-brazed CuW tip
Refurbishment
For installed breaker fleets, match the original arm configuration and material. Send the original drawing or a sample; substituting a different material changes the arm's current rating and the breaker's certified performance.
Related Reading
- Conductor Material Selection Guide: broader conductor material decisions
- Contact Arms (Category): full product range