Electrical Contacts & Connectors - a comprehensive design and user guide

Connectors and contacts encompass a wide range of electrical components including switch and relay contacts, plug and socket connectors, crimp connections and circuit breakers. These are used to make electrical connections from a few micro-volts and micro-amps up to thousands of volts and amps or more. Some connectors may be inserted and withdrawn very rarely, whereas some switch contacts may need to operate for 109 operations.

The design of contacts and connectors and the optimum choice of materials used depends on a variety of factors, which are discussed in detail in this report. These include the current, voltage, wear, oxidation and corrosion and damage due to heat and arcing. The final choice will depend on all of these issues as well as the cost of the materials of construction.

This report discusses the physics of electric contact. Physical contact is usually made by a number of very small points or asperities. The total area in contact can be very small, so melting or boiling at the surface can occur with relatively low currents. Wear depends on a variety of physical parameters including the hardness. Loss of the surface can be very damaging as many connectors and contacts have thin films of precious metals as the top layer. At higher voltage and current, arcing occurs. Arc erosion is limited by careful choice of contact materials and some special composite materials have been developed which have long service lives despite arcing. Higher currents can also lead to welding of contacts. The correct choice of materials is essential for maximising the performance of a contact or connector. Silver composites with various metal oxides are very resistant to arc erosion but the contact resistance is much higher than gold. Switch and connector manufacturers spend a great deal of time trying to find lower cost alternative materials and designs for their products.

Currently auto electronics, especially in the engine compartment, use gold plated connectors as other materials deteriorate in these hostile conditions. However, there is a lot of effort into replacing gold with a lower cost material. In the future, it is possible that automotive electrical systems will change from 12 volts to 42 volts. This will put an increased strain on the materials used for switching contacts as arcing is more likely.