AgW vs CuW: When to Use Silver Tungsten vs Copper Tungsten
Silver tungsten (AgW) and copper tungsten (CuW) are sister materials in the tungsten-composite electrical contact family. Both combine a tungsten skeleton with a softer matrix metal infiltrated through powder metallurgy; both deliver arc-erosion resistance that pure copper or pure silver couldn't match. The difference between them, silver matrix vs copper matrix, sounds small but shows up in conductivity, cost, and which applications each one belongs in.
For engineers and procurement specifiers facing the choice, the question usually comes up at the application boundary between low-voltage (LV) electrical apparatus and medium-voltage (MV) switchgear. This article walks through what drives the choice and where each material is the right answer.
The Quick Answer
If you're skipping to the bottom line:
- AgW for low-voltage electrical apparatus: contactors, motor starters, relays, LV circuit breakers. Silver matrix gives lower contact resistance, which matters in continuous LV operation.
- CuW for medium-voltage vacuum interrupters and switchgear: VCBs, vacuum interrupter contacts, MV disconnectors. Copper matrix is significantly cheaper; arc duty dominates the trade-off at MV.
The application class (LV vs MV) usually settles the question. Material grade selection within each family (AgW70 vs AgW80, CuW70 vs CuW80, etc.) is a separate decision covered in other articles.
Why the Matrix Metal Matters
Both AgW and CuW have a tungsten skeleton, typically 30 to 90 wt% tungsten, providing arc-erosion resistance and mechanical strength. The difference is what fills the pore space:
- Silver in AgW: higher electrical conductivity than copper (silver is the most conductive metal at typical conditions), better corrosion resistance, much higher material cost.
- Copper in CuW: lower conductivity than silver but still excellent, lower cost, better thermal conductivity for high-current applications.
The matrix metal dominates the composite's electrical behavior because current preferentially flows through the conductive matrix rather than the tungsten skeleton. At the same tungsten content, AgW always has higher conductivity than CuW.
Per GB/T 8320-2025 minimums:
| Grade | Tungsten | AgW Conductivity ≥ (% IACS) | CuW Conductivity ≥ (% IACS) |
|---|---|---|---|
| 70 | 70 wt% | 45 | 42 |
| 75 | 75 wt% | 41 | 38 |
| 80 | 80 wt% | 37 | 34 |
The conductivity gap (3–4 percentage points across grades) is modest but consistent. At lower tungsten content (e.g. AgW30 at ≥75% IACS vs CuW50 at ≥54% IACS), the gap widens because the silver matrix dominates more of the cross-section.
Cost Difference
Silver is significantly more expensive than copper as a raw material. The price gap fluctuates with commodity markets but silver historically runs roughly two orders of magnitude more expensive than copper per kilogram. For a contact with 30 wt% matrix metal (e.g. AgW70 or CuW70), the matrix metal cost difference dominates the price gap between the two materials.
Per-piece cost depends on the specific dimensions, plating requirements, manufacturing complexity, and order volume. But as a rough rule: AgW costs noticeably more than CuW for the same geometry and tungsten content. This cost difference is the primary reason CuW dominates MV switchgear applications, where AgW's conductivity advantage doesn't justify the cost premium.
Application Boundary
The AgW vs CuW decision aligns with the LV vs MV application boundary almost cleanly:
Low-Voltage Apparatus (Below 1 kV)
LV contactors, motor starters, relays, and circuit breakers operate at voltages below 1000 V. At these voltages:
- Continuous-current heating is the dominant electrical concern. Lower contact resistance directly translates to less heating, lower temperatures, and longer service life.
- Arc duty is less severe per operation than at MV. The arc has less energy to deposit on the contacts; tungsten skeleton resistance is more than sufficient.
- Apparatus is high-volume, millions of contactors per year across the industry. Per-piece cost matters more than absolute peak performance.
AgW dominates here because the silver matrix's higher conductivity has a real impact on apparatus thermal behavior, and the cost premium is acceptable in the high-volume LV market.
Medium-Voltage Switchgear (1 kV to 52 kV typically)
MV switchgear, VCBs, vacuum interrupters, MV disconnectors, operates at voltages from 1 kV up to roughly 52 kV in distribution and substation applications. At these voltages:
- Arc duty is the dominant concern. A vacuum arc at MV deposits substantially more energy per event than an LV arc; arc-erosion resistance matters more than minor conductivity differences.
- Continuous-current heating is a concern but the cost-effective solution is sizing the contact cross-section appropriately, not switching to a higher-conductivity matrix.
- Apparatus is lower volume than LV. Per-piece cost matters but capital cost of the breaker is high enough that material cost optimization in the contact is a smaller portion of total breaker cost.
CuW dominates here because the cost savings vs AgW are significant, and the conductivity disadvantage is manageable by adjusting contact size.
Boundary Cases
A few specific applications sit on the boundary:
- LV air circuit breakers (ACBs) at high current: 400V–1000V ACBs at 2000–6000 A continuous currents can specify AgW70 or AgW80 for high-cycle severe-duty applications, where the higher tungsten content matches the arc duty and silver matrix keeps continuous-current heating manageable.
- High-current LV contactors for motor starting: Same logic, AgW70 / AgW80 for severe duty motor starters.
- Specialty MV applications: Very rare, but AgW has been used in some specialty MV designs where the contact's specific role (e.g. very low duty cycle, exposed to atmosphere rather than vacuum) makes silver's corrosion resistance valuable.
For your specific application, the voltage class is the first thing to check. Below 1 kV → AgW. Above 1 kV → CuW (almost certainly).
Form Factor Differences
AgW and CuW are also used in different physical forms in practice:
AgW Typical Forms
- Contact tips brazed onto copper alloy carriers in LV contactor moving and fixed assemblies, see AgW Contact Tip
- Riveted contact buttons for high-volume LV apparatus assembly, see AgW Contact Rivet
- Bimetallic contacts (AgW on a steel or copper backing) for cost-sensitive high-volume builds
CuW Typical Forms
- Whole arc contacts in vacuum interrupters, static and moving contact bodies, see CuW Static Arc Contact
- Brazed contact tips on copper conductor carriers in MV switchgear
- Shielding caps inside vacuum interrupters, see CuW Shielding Cap
The form factor difference reflects manufacturing economics in the two markets: high-volume LV apparatus uses small contact tips and rivets for fast assembly; lower-volume MV switchgear uses larger machined contacts with more individual customization.
When to Use Both
A few MV apparatus designs use AgW in specific roles within an otherwise CuW-dominated system. For example, the static arc contact in a vacuum interrupter is CuW (handles the arc), while small AgW elements may appear at certain interface points. These are rare specialty designs; the boundary is well-defined enough that 95%+ of applications fall cleanly into AgW (LV) or CuW (MV).
What to Specify When Sourcing
For either material, the basic specification is:
- Voltage class and application (to confirm the right material family)
- Tungsten content (e.g. AgW70 or CuW70)
- Form factor (tip, rivet, whole contact, custom geometry)
- Dimensions per drawing
- Mounting interface (brazed-on carrier, riveted, integrated)
- Plating or surface treatment if required
If you're unsure which material applies to your application, send the apparatus type and voltage class. We can recommend.
Summary
AgW for LV. CuW for MV. The split aligns with the application's dominant electrical concern: contact resistance in continuous LV operation (favors silver matrix) vs arc-erosion resistance at MV (favors cost-effective copper matrix). Cost differences make this an economic decision as much as a technical one. Silver is dramatically more expensive than copper, and the cost premium has to be justified by application requirements.
For LV contactors, motor starters, and relays, see the Silver Tungsten (AgW) Series. For MV vacuum interrupters and switchgear, see the Copper Tungsten (CuW) Series.
Related Reading
- Choosing AgW Grade for AC Contactors: AgW grade selection within the LV apparatus market
- How to Choose CuW Grade: CuW70 / 75 / 80 selection guide
- Silver Tungsten (AgW) Series: Full AgW product range
- Copper Tungsten (CuW) Series: Full CuW product range