One of the features of copper metallurgy is that copper can be easily alloyed with other metals. The addition of about 1 per cent of cadmium results in an alloy which has a considerably higher tensile strength than electrical grade copper although there is a slight reduction in conductivity.
Cadmium copper trolley wires were used almost exclusively for tram and trolleybus services, both in London and in the provinces for many years until these vehicles were replaced by buses. Cadmium copper was also used during the original construction of the National Grid between the Wars - notably for river crossings such as the one at Dagenham where seven cables were suspended across the Thames from towers 487 ft. high. Today, this same alloy is being used extensively for catenary wires and contact wires in the overhead electrification systems of British Railways; and for railways abroad. It has been estimated that for every 100 miles of electrified track 2500 tons of copper and cadmium copper may be required.