Here is a view of it with the bottom opened. Anyone know what this was used for and/or the history behind it?

I picked this interesting object up on the weekend from a hydro man. It weighs 9 pounds, has a porcelain cover and a metal bottom. On the metal bottom is engraved N. Slater Co./ Hamilton/Canada/CAT NO 12/60 amperes/5000volts. The metal bottom pulls open (see second picture) and reveals several knobs, springs and wires. Any idea what this was used for? Anyone know what the history behind it is? Thanks!