What are contact instability and contact failure caused by carbide?

ID: FAQE10081E



As the load is opened and closed, carbide (carbon) is generated and deposited on the contact, causing contact instability and contact failure.
In particular, it is susceptible to organic gas, and contact failure is likely to occur in the operating environment or when opening and closing a microload.


When opening and closing a microload, the cause of relay contact failure is a film formed on the contact due to the effect of organic gas in the operating environment.
Organic silicon gas in particular is highly permeable and can penetrate the inside of the relay, resulting in contact failure.

  • Microload opening/closing
    When the load is switched at a low voltage of several hundred mA or less, there is no arc during switching and switching occurs at the glow discharge level. In the case of opening and closing such a microload, there is no activation (cleaning) effect that scatters the carbon generated during switching from the contact area.
    If the load is more than a few A, the contact part which scatters the carbon by the arc current is activated, reducing the fluctuation of the contact caused by the carbon.

When the load current is reduced to several hundred mA or less, energy is insufficient to cause the arc between contacts. The contact arc has the effect of removing carbon generated on the contact. Carbon accumulates on the contact if no arc occurs, causing contact instability and contact failure. Select an appropriate relay when considering microload switching.

Switching by microload to several hundred mA
Switching by several A to dozens A
  • Operating environment
    Avoid use in an organic gas atmosphere.

Regarding to Mnimum load application, see Relay Basics: General Application.

Quick tips

  • Select a relay with a contact structure suitable for microload switching.
    Ag alloy < Ag < Au-plated (clad) < Au-plated (clad) crossbar twin structure
  • Select a relay less susceptible to ambient environments.
    Flux resistant < Plastic sealed
Product category Relays Signal Relays Power Relays
Classification Trouble shootings
Related keywords
  • Signal relay
  • Power relay
  • Contact failure
  • Film formed on contacts
  • Carbon

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