When panel builders compare push button switches, the conversation usually covers head profile, contact configuration, IP rating, and price. Contact material rarely comes up — it’s buried in the datasheet, if it’s listed at all. But contact material is one of the factors that most directly determines how a switch performs over its service life, particularly in the low-current signal circuits that dominate modern industrial control panels.
This blog explains what silver-plated contacts are, why they became the standard for industrial push button switches, where they have limits, and what to ask a supplier when contact material actually matters for your application.
What Happens at the Contact Surface
A push button switch works by physically closing a gap between two conductive surfaces. The contact surface faces several simultaneous stresses every time the switch operates:
Mechanical Wear
The two contact surfaces press together and separate repeatedly. Over millions of cycles, this causes physical erosion of the contact material.
Electrical Arcing
When contacts open under load, current continues to flow across the gap as an arc for a brief moment. This arc generates localized heat and erodes the contact surface faster than mechanical wear alone.
Oxidation
Most metals oxidize when exposed to air, forming an insulating layer that increases contact resistance. In low-current circuits, oxidation can increase resistance enough to prevent the circuit from functioning at all.
Contamination
Industrial environments contain oils, cleaning agents, dust, and humidity — all of which increase resistance and can cause intermittent connection.
Why Silver
Silver has two properties that make it the dominant contact material in industrial switching:
Lowest electrical resistivity of any metal. Silver conducts electricity better than copper, gold, or any other commonly used contact material — less voltage drop, less heat, and better performance in low-current signal circuits.
Relatively stable oxide. Most metal oxides are hard insulators. Silver oxide is an exception — it remains electrically conductive. A copper contact that has oxidized may refuse to make a reliable circuit at low current. A silver contact that has oxidized will typically still conduct.
These two properties explain why silver replaced copper as the standard contact material for relay and switch contacts, and why it remains dominant today.
Silver-Plated vs. Silver Alloy vs. Gold-Plated
Silver-Plated Contacts
A base metal core — usually copper or brass — with a layer of silver on the contact surface. The plating provides silver’s electrical performance while the base metal provides structural strength. This is the most common approach for general industrial push button switches.
Silver Alloy Contacts
Alloys such as silver-cadmium oxide (AgCdO) or silver-tin oxide (AgSnO₂) improve arc resistance and reduce contact welding at higher currents. More common in contactors and heavier switching devices than in push button switches.
Gold-Plated Contacts
Gold doesn’t oxidize at all, making it the preferred material for very low current signal circuits — typically below 100mA. Used in instrumentation and dry circuit switching where even conductive silver oxide can cause problems.
For standard push button switch applications — PLC inputs, relay coils, contactor auxiliary circuits — silver-plated contacts are the appropriate choice.
Where Silver-Plated Contacts Have Limits
Very Low Current Dry Circuit Switching
In circuits carrying less than approximately 100mA, even silver oxide can create enough contact resistance to affect circuit behavior. The self-cleaning arc that normally keeps contacts clean doesn’t occur at these levels. Gold-plated contacts are the correct specification for dry circuit switching.
Aggressive Chemical Environments
Silver tarnishes rapidly when exposed to hydrogen sulfide and sulfur compounds. In chemical processing or rubber manufacturing environments, silver contacts may degrade faster than expected. Gold-plated contacts or a well-sealed enclosure are the appropriate response.
High Ambient Humidity with Infrequent Operation
Contacts that are regularly switched self-clean through the wiping action at make and break. Contacts that sit unused for long periods in humid environments accumulate oxidation faster. Gold-plated contacts or a regular test actuation schedule address this.
Practical Guidance for Specifiers
What current will the contacts switch? For standard PLC inputs and relay coils at 24V DC or above, silver-plated contacts are appropriate. For signal-level or dry circuit applications below 100mA, specify gold-plated contacts.
What is the switching frequency? High-cycle applications place more demand on contact surfaces. Confirm the electrical life rating — not just mechanical life — at the actual load current your circuit will carry.
What is the environment? Standard industrial environments are well within the capabilities of silver-plated contacts. Chemically aggressive or high-humidity low-usage environments may warrant gold-plated contacts.
What load type are the contacts switching? Resistive loads are easier on contacts than inductive loads. Confirm the contact rating against your actual load type — most datasheets specify both AC-15 (inductive AC) and DC-13 (inductive DC) ratings separately.
At ACXION, push button switches are available with standard silver-plated contacts and optional gold-plated contacts for dry circuit applications. Contact us with your application details and we will recommend the right configuration.