Choosing the Right AgW Grade for AC Contactors
AgW (silver tungsten) is the standard contact material for AC contactors across the low-voltage electrical apparatus market. The choice isn't whether to use AgW. It's which grade. AgW30, AgW40, AgW50, AgW70, AgW80, five common grades cover the practical range, and each fits a specific category of contactor application.
For design engineers specifying contactors and procurement specifiers ordering replacement contacts, picking the right grade affects three things: contact resistance during normal operation, service life under repeated switching, and per-piece cost. This article walks through how to decide based on application duty.
The Available Grades
Per GB/T 8320-2025 Table 6 minimums, the AgW grade range:
| Grade | Silver Content | Tungsten | Conductivity ≥ (% IACS) | Density ≥ (g/cm³) | Hardness ≥ (HB) |
|---|---|---|---|---|---|
| AgW30 | 70±1.5% | balance | 75 | 11.75 | 80 |
| AgW40 | 60±1.5% | balance | 66 | 12.40 | 90 |
| AgW50 | 50±2.0% | balance | 57 | 13.15 | 110 |
| AgW55 | 45±2.0% | balance | 54 | 13.55 | 120 |
| AgW60 | 40±2.0% | balance | 51 | 14.00 | 130 |
| AgW65 | 35±2.0% | balance | 48 | 14.50 | 140 |
| AgW70 | 30±2.0% | balance | 45 | 14.90 | 155 |
| AgW75 | 25±2.0% | balance | 41 | 15.40 | 170 |
| AgW80 | 20±2.0% | balance | 37 | 16.10 | 185 |
The pattern is the same as for CuW: more tungsten means higher density, higher hardness, better arc-erosion resistance, but lower conductivity and higher cost.
For AC contactor applications specifically, the practical range is AgW30 through AgW80. AgW75 is rare in standard contactor designs; the others (AgW40, AgW50, AgW55, AgW60, AgW65) cover the spectrum of contactor duty classes.
What Determines the Right Grade
AC contactors handle four basic duty patterns, and each maps roughly to a grade range:
Light Duty: Distribution Contactors at Modest Current
For 9 A, 12 A, 18 A class general-purpose AC contactors handling lighting circuits, small heating loads, and similar:
AgW30 or AgW40 is typical. Light arc duty per operation means tungsten content can be low; conductivity matters for thermal performance in compact contactor designs.
These applications cycle a few times per day at most, with peak currents at or just above the rated continuous current. Service life is more limited by mechanical wear than by arc erosion.
General-Purpose Duty: Standard Industrial Contactors
For 25 A, 32 A, 40 A class contactors handling general industrial loads, intermittent motor duty, and routine switching:
AgW40 or AgW50 is typical. Moderate arc duty, moderate cycle count. Contact resistance still matters for thermal performance; arc-erosion resistance becomes more relevant as cycle counts increase.
AC-3 / AC-4 Motor Duty: Direct-On-Line Motor Starters
For contactors operating motors in AC-3 (squirrel cage motor starting) or AC-4 (motor starting and reversing) duty per IEC 60947-4-1:
AgW70 is the typical specification. Motor starting cycles produce high inrush currents (typically 6–8x motor rated current) and the contactor breaks the inductive load when the motor stops or trips. This is severe arc duty; the higher tungsten content extends contact life proportionally.
For frequent-start applications (jog duty, soft-start ramping, process applications with high duty cycle), AgW70 is the standard. Lower grades wear too fast under repeated arc cycles.
Heavy Duty: Reversing Starters, Industrial Brake Switching
For contactors in reversing duty (plug stopping, frequent direction reversal), industrial brake switching, or AC-4 duty with very high cycle counts:
AgW70 or AgW80 depending on the specific application. AgW80 trades more conductivity for more arc-erosion resistance. For severe duty applications, AgW80 extends service life noticeably; the cost premium and higher contact resistance are accepted.
LV Air Circuit Breakers
Low-voltage air circuit breakers (ACBs) at higher current ratings (typically 1000 A and above) often use AgW70 or AgW80 contacts. The duty cycle is lower than a motor contactor (ACBs operate less frequently) but the fault current handling capability requires the higher tungsten content to survive worst-case operations.
Application Mapping Summary
| Contactor Class | Typical AgW Grade |
|---|---|
| Light-duty distribution contactors (9–18 A) | AgW30, AgW40 |
| General industrial contactors (25–80 A) | AgW40, AgW50 |
| AC-3 motor starters (any size) | AgW70 |
| AC-4 / reversing motor starters | AgW70, AgW80 |
| Severe-duty industrial process contactors | AgW80 |
| LV ACBs (1000 A and above) | AgW70, AgW80 |
| LV relays (general purpose) | AgW30, AgW40 |
This mapping covers most standard applications. For specialty applications or unusual duty cycles, the right grade may differ, discuss with your apparatus engineer or send the duty specification.
Other Selection Factors
Form Factor
AC contactors typically use AgW in one of two physical forms:
- Brazed-on contact tips (AgW Contact Tip), AgW tip brazed onto a copper alloy carrier in the contactor's moving and fixed contacts
- Riveted contact buttons (AgW Contact Rivet), AgW button with a pre-formed mounting head, riveted into the contactor at assembly
For high-volume contactor production, riveted buttons are typical. For lower-volume or higher-customization production, brazed tips offer more design flexibility. The form factor doesn't change the grade selection logic; specify the form factor independently of the grade.
Plating
AgW contacts are usually supplied as machined, with no additional plating on the contact face. The silver matrix already provides the low-resistance contact surface; additional silver plating is uncommon. Some specialty applications add gold flash for environmental sensitivity, but these are rare in general contactor manufacturing.
Bimetallic Construction
For cost-optimized contactor manufacturing, AgW + copper bimetallic contacts put the expensive AgW only on the arc face, with cheaper copper backing handling the bulk current path. Bimetallic options:
- AgW + Cu (most common; cost optimization)
- AgW + steel (mechanical strength for rivet shanks)
If your application volume justifies the tooling for bimetallic contacts, the cost savings on AgW content are real.
Compatibility with Existing Contactor Designs
For refurbishment or repair contracts, match the original contactor's specification. Apparatus manufacturers test their contactor designs with specific AgW grades; substituting a different grade can change the apparatus's certified ratings (AC-1, AC-3, AC-4 ratings per IEC 60947-4-1 are tied to the specific contact material as tested).
For new contactor designs, the grade choice is part of the apparatus design process. Test prototypes with the intended grade and validate against the target ratings.
Cost vs Grade
Higher-tungsten AgW grades cost more per piece, primarily because of manufacturing complexity rather than raw material content (silver is the expensive component, and lower-tungsten grades have more silver). The relative cost gradient across grades is modest, picking AgW70 over AgW40 is a meaningful per-piece cost increase but not a dramatic one.
The total contactor cost depends on contactor size, contact dimensions, plating, and quantity. For specific pricing, send the contactor design or the replacement specification.
Specifying When Sourcing
For an AgW contact quote, include:
- AgW grade (e.g. AgW70 for motor starter duty)
- Form factor (tip, rivet, custom geometry)
- Dimensions per drawing
- Mounting interface (brazed onto carrier, riveted, or custom)
- Contactor type and rating (helps confirm grade choice)
- Quantity and intended use (single batch, recurring production, refurbishment)
For standard contactor applications, our AgW Contact Tip, AgW Contact Rivet, and AgW70 Heavy-Duty Contact cover the most common form factors and grade ranges. Custom geometries from drawing are routine.
Summary
AgW grade selection for AC contactors maps to application duty: light duty uses lower-tungsten grades for higher conductivity; heavy-duty motor starting uses AgW70 or AgW80 for arc-erosion resistance. Most general industrial contactors fall in the AgW40–AgW50 range; AC-3 / AC-4 motor duty calls for AgW70; severe-duty applications justify AgW80. For specific guidance on your application, send the contactor specification and intended duty cycle.
For grades outside the AgW family, when you're moving from LV to MV apparatus, see AgW vs CuW: When to Use Each.
Related Reading
- AgW vs CuW: When to Use Each: Material family selection for LV vs MV applications
- AgW70 Heavy-Duty Contact: AgW70 product for motor starter duty
- AgW Contact Tip: Standard AgW tip for general contactor applications
- AgW Contact Rivet: Riveted AgW button for high-volume production
- Silver Tungsten (AgW) Series: Full AgW product range