The refillable BA type (boric acid) high voltage expulsion fuse is an E-rated fuse that can be vented (outdoor) or enclosed (indoor). These fuses are designed for power applications and were introduced by the Westinghouse Electric Company in the middle 1930's. The refill units have been in continuous production since that time and are still available for use in existing installations. Mountings are no longer available for use with BA refill units, but a limited range of replacement fuse holders is still available. New and replacement applications should use RBA fuses that superseded BA fuses a number of years ago.