antique early industrial/architectural fuse holder with mica bottom socket

Antique early electrical vintage fuse block holder for industrial or architectural installations. The Edison socket for holding the screw in fuse has a mica bottom. The bottom is gray porcelain and is marked "PC No 31574" and "Made in USA" on the back. There is no name or date that we could find. It measures 4.5" x 3.375" across the base and is marked on the top for "line" and "load".