Switchgear standardization

General principles underlying standardization. Standard test pressure for switch and controlling gear. Conductivity of current-carrying alloys : specifications of cast brass and gunmetal. Knife switches : millivolt drop at contacts. Suggested standards for back connection studs and nuts. Oil switches and circuit-breakers : urgent necessity of standard oil-switch rules in view of the position in foreign countries; breaking capacity; connection between breaking capacity and quantity of oil. Resistance and reactance type of oil circuit-breakers. Length of break of oil switches. Single and multiple tanks on oil switches. Amount of oil required for oil switches. Speed of operation of oil circuit-breakers. Air-break circuit-breakers : millivolt drop at brush contacts. Cut-outs: National Electric Code enclosed cut-outs; short-circuit tests on cut-outs; time element of cut-outs; determination of normal fusing current. Resistance wire: suggested British copper-nickel standards. Motor starting-gear; liquid starters. Copper strip connections of switchboards: suggested standard sections; temperature rise; millivolt drop of bolted contacts. Switchboards: cellular principle; suggestions put forward by Swiss Electrotechnical Society. Lightning protective gear : horn gaps; choking coils; lightning arresters.