Electrical Contacts Information
How to Select Electrical Contacts
Electrical contacts are soft, high-conductivity, oxidation-resistant materials used as the makeup of electrical components. They are the materials in a system through which an electrical current flows.
Types of Electrical Contacts
The GlobalSpec SpecSearch Database contains categories for these types of electrical contacts.
- EDM electrodes are used in electrical discharge machining (EDM), a process that removes metal with an electrical discharge of very short duration and high current density between the electrode and the workpiece.
- Welding electrodes are designed for resistance, arc, or plasma welding.
- Furnace electrodes are used to heat and melt metals or ceramics in arc furnaces. An arc is struck between the electrodes and furnace load material. The arc or plasma generates extremely high temperatures. The electrodes are commonly made from carbon-based materials.
- Electrical brushes are used in conjunction with slip rings and other contact surfaces to maintain an electrical connection in mobile or rotary applications. Graphite brush materials are used typically for high-power equipment. Metal brushes or sliding contacts are used for signal or low power applications.
- Electrical contacts consist of a high-conductivity, soft, and oxidation-resistant material, often with a second phase to provide anti-welding and/or arc-resistance. They are used in circuit breakers, relays, switches, and EDM applications.
- Contact probes are contact or brush assemblies consisting of a contact with an integral spring that maintains sufficient contact force to assure low contact resistance. Contact probes and spring contacts typically have a plunger type configuration with an internal helical spring. Contact probes and spring contact are used in ATE test probe and battery contact applications.
- Battery contacts are designed for battery-contact applications. The contact often consists of a low-cost base metal such as steel or brass with a plated layer of high-conductivity or corrosion-resistant metal.
Metals and Materials
Electrical contacts are generally made from metals with high electrical conductivity, except in applications such as high-power equipment brushes where abrasive wear is expected. The most commonly used metal surfaces for contact alloys are silver, copper, gold, platinum, and palladium. Tungsten, nickel, graphite, and molybdenum are materials that enhance the structural properties of highly conductive metals and some are used individually for specialized contacts and components.
Important properties of electrical contact are conductivity, corrosion resistance, hardness, current load, form, and size. Many of these are determined by inherent characteristics of the material.
- Conductivity is the measure of a material’s ability to carry or conduct an electric current. It is often given as percent of a copper standard, which is 100% IACS, (International Annealed Copper Standard). Silver has an IACS of 105 and has the highest conductivity.
- Corrosion resistance is the material’s ability to resist chemical decay. A material that has little corrosion resistance will likely decay away noticeably and will have a shorter lifespan.
- Hardness is the measure of how resistant the material is to various kinds of permanent deformations resulting from an applied force. Hardness is dependent on a material’s ductility, elasticity, plasticity, tensile strength, and toughness.
- Current load is the maximum recommended current load that the material is capable of handling. For static contacts or connectors, rated current is the current that a device can carry continuously without overheating. For opening and closing contacts in devices such as circuit breakers, contactors, or switches, rated current is the current a device can carry while switching.
- Form refers to the shape an electrical material must fit in order to carry out its operation. Some shapes include contact tips, pins, sockets, stampings, sheets, wires, and wheels.
- Size relates to the thickness, length, and width or outer diameter of the form a material takes.
Another specification to consider is toxicity, particularly important when the material is operating in exposed or open environments.
Applications of Electrical Contacts
Electrical contacts are present in any system in which a transfer of electricity occurs. Specific examples include circuit breakers, relays, switches, and electrical discharge machining (EDM) applications.