have lower contact ratings for tungsten loads than for purely resistive loads. An electrical arc across relay contacts can be very hot — thousands of degrees Fahrenheit — causing the metal on the contact surfaces to melt, pool, and migrate with the current. The extremely high temperature of the arc splits the surrounding gas molecules, creating ozone, carbon monoxide, and other compounds. Over time, the arc energy slowly destroys the contact metal, causing some material to escape into the air as fine particulate matter. This action causes the material in the contacts to degrade and coordination, resulting in device failure. This contact degradation drastically limits the overall life of a relay to a range of about 10,000 to 100,000 operations, a level far below the mechanical life of the device, which can be in excess of 20 million operations. See also Analogue switch Buchholz relay Dry contact Flyback diode Nanoelectromechanical relay Race condition Stepping switch Wire spring relay References External links 1835 introductions Electromagnetic components Power engineering 19th-century inventions German inventions American inventions