It has been realized for some time that fire risk in electrical installations involves special consideration owing to the nature of the combustible materials involved. Preliminary study of the problem resulted in the risks being divided into four categories, and a series of tests was undertaken with varying available media and different installations in each category. This paper describes briefly the test installations designed and erected for this purpose and gives a general outline of the testing technique involved. Tables are given showing the results of the tests, with explanatory notes where necessary for each test. The paper concludes with a discussion of the test results, and general recommendations are given in regard to the various categories of risk tested.