THE standards of the American Institute of Electrical
Engineers define an oil circuit breaker as a
"device (other than a fuse) constructed primarily
for the interruption, in oil, of a circuit under infrequent
abnormal conditions/' Common usage, however, has
sanctioned the use of the term "circuit breaker" as
applying to a device for the regular and usual interruption
of an energized circuit as distinguished from a
switch used only for opening circuits which are deenergized
or not carrying load. This paper will consider
only high-voltage oil circuit breakers, the term
"high voltage" being taken as applying to potentials
of 25,000 volts or above.