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As a result of the large development which has been made in the relay practises in the last few years, the Protective Devices Committee felt it was desirable to make an analysis, of the transmission line protective relay situation throughout the country and prepare a summary to bring before the profession, experiences of the operating companies with this protective apparatus. With this in view questionnaires were sent out to sixty-one operating companies asking for their experience and present practise in regard to relay protection. Replies were received from 32 of the operating companies and from these the following general analysis was made of the practise of relay protection for transmission lines. The nomenclature used by the different operating and manufacturing companies for the various classes of relays is not in harmony and the Protective Devices Committee undertook the work of standardizing the nomenclature which it is hoped will be adopted by all parties so that any particular class of relays will be given a definite name. The following nomenclature has therefore been proposed by the Protective Devices Committee and this nomenclature is used throughout this paper.