This an absolute brute of a transformer. I would assume it powered a large number of bells. The bells would have definitely had to be switched by a heavy duty relay . Possibly with mercury contacts. Unlike the lower wattage smaller versions with cartridge fuses on the outputs ,this one has Slydlok re wirable fuses. I assume the idea was to give a delay blowing ,
unlike cartridge fuses. I would tend to think this could date back to the late 40s. It was definitely designed pre National Grid. The mains universal frequency is the clue on the label. It also has a Lead Cable Clamp fitted . Probably for a large cable . At least 7/.029 . Andy