During the year 1921 the number of cable failures on the 20,000 volt lines was about one per hundred miles. This was about the same as there cordon the 9000 volt cables, and this result leads to the conclusion that when the transmission cables are operated at safe loads, in the determination of which dielectric losses have been given proper consideration, the resulting failures are of the order of one per hundred miles per year. This result indicates that very few of the cable failures which have occurred in the past are due to dielectric stresses and that most of the failures occur due to the reduction in dielectric strength caused by the heating of the cables above their critical temperature.