Design, performance and application of miniature circuit-breakers

The paper is intended as a critical survey of the technical and economic aspects of miniature circuit-breakers. After some introductory remarks on their place in the field of protective gear, a brief historic outline of their development is given, followed by an analysis of the many requirements to be met, together with a study of the more important design features to be observed concerning contacts, arc-extinguishing devices, mechanism, etc. Special attention is devoted to overloads and short-circuit-protection devices, and the rupturing capacity is reviewed in some detail. The application and economy of these circuit-breakers are discussed on a basis of comparison with other protective gear, and with the practice followed in the United States. In conclusion, some suggestions are made for the future development of miniature circuit-breakers in the belief that they will occupy a place of constantly increasing importance.