Electrical contact material selection

Electrical contacts for motor controls are usually made from copper.  When contacts are in the closed position for a long period of time, accompanied by a healthy flow of amperage, they tend to 'stick'or weld.  Silver or silver-alloy pads are often brazed onto the copper base at the mating point to help resist sticking and welding of the movable and stationary contacts.  The material composition of these silver pads affects performance.  It’s often a balancing act between operational requirements and the longevity and durability of the contact itself.  To combat contact welding, the silver is often blended with other metals creating highly conductive but wear-resistant alloys.

Pure Silver

Pure silver can be used, but is not the material of choice in most applications.  The exception would be fine silver for specialized DC contactors.  

Silver Cadmium-Oxide

This alloy is found in percentages of 85% -15% or 90% - 10%.  The cadmium oxide is added for increased resistance to welding.  This material is found in most AC contactors from NEMA sizes 00 through size 6.  

Silver-Tungsten:

This alloy is usually found in a 50% - 50% ratio.  Tungsten is extremely hard.  It's rare to find silver contacts that have welded together.  The primary applications for this material are circuit breakers and high amperage contactors.  Silver’s superior conductivity combined with tungsten’s resistance to mechanical and electrical wear also makes this alloy an excellent choice for harsh environments where oxidation and arcing are expected.

Repco’s replacement contacts match the OEM’s

Repco’s replacement contacts are reversed engineered to replicate the form, fit, and function of the OEM contacts.  Repco utilizes the same contact material as the original manufacturers.  Contact Repco today to see how you can save money and improve your electrical contact selection for multiple applications.