exceptional early 20th century oversized solid copper american industrial switchboard knife switch designed and fabricated by the trumbull electric mfg. co., plainville, ct. the three pole punched clip knife switch does not require a fuse. the double throw has a 250v/1000amp rating. the massive switch was salvaged from a 1915 chicago commercial building basement open switchboard the blades are intact and in great condition, considering age. the original slate board was badly damaged prior to removal. the contacts are said to be 'closed' when there is no space between them, allowing electricity to flow from one to the other. when the contacts are separated by an insulating air gap, an air space, they are said to be 'open', and no electricity can flow at typical voltages. original turned and tapered wood handle retains the original black enameled finish. the nonconductive crossbar is made of a hardened composite. lightly imprinted manufacture markings easily identified. lightly cleaned.