THE safety of every electricity supply system depends on its switchgear always being ready to operate. The main switches (circuit-breakers) must always be capable of making and breaking the current, and still remain fit for use. The development of the grid system has proved the necessity of being able to ‘clear’ a fault even when fed by enormous currents. For many years, the firms now constituting Associated Electrical Industries have had extensive experience of short-circuit tests made with generators having capacities up to 80,000 kilovolt amperes. In an article in Electrical Industries of October 14, a description is given of a testing station having a generator capable of giving 2,500,000 k.v.a. on short circuit. In order to meet the demand for more tests and for tests at higher powers, the companies interested combined to form a separate company known as the Switchgear Testing Co., Ltd., which now owns and operates the plant on their behalf. The testing station is situated at Trafford Park, Manchester. Ample space had to be provided to ensure personal safety, and, when ‘testing to destruction’, to avoid damage to property by explosion and fire. The station has three testing areas; two are covered over and used for testing up to 33 kv., and one is an open area, testing up to the grid voltage of 132 kv. The station has a complete equipment for measuring and recording phenomena. Its electromagnetic oscillograph has sixteen elements and is probably the only oscillograph of this kind in the world. It is satisfactory to know that these companies have taken a leading part in conjunction with other firms both in Great Britain and abroad in producing a standard specification for procedure in testing circuit breakers which is recognized internationally.