Hawkins Electrical Guide v. 06 (of 10) / Questions, Answers, & Illustrations, A progressive course of study for engineers, electricians, students and those desiring to acquire a working knowledge of electricity and its applications

by N. Hawkins

Figs. 1,976 and 1,977.—Westinghouse double pole fuse box; views showing box open with tubes in place, and with tubes removed.

Transformer Fuse Blocks.—These may be of either the single pole or double pole type. Fig. 1,976 shows a double pole fuse box opened, and fig. 1,977, the fuse box opened and the tubes removed. Of the four wires, W, W, W, W, entering the box from beneath, two are from the primary mains, and two lead to the primary coil of the transformer. These wires terminate in metallic receptacles R, R, R, R, in the porcelain plate P, fig. 1,977, which are bridged over in pairs by fuse wires placed inside porcelain tubes T, T, as shown in fig. 1,976. These tubes are air tight except for a small outlet O in each, which fit into the receptacles B, B, in the porcelain plate and open out at the back of the block, as shown in fig. 1,977.

The fuse wires are connected between metallic spring tubes S, S, S, S, which fit into the receptacles R, R, R, R.

If a sudden load or a short circuit occur in the transformer, the intense heat, accompanying the melting or blowing of the fuse, causes a rapid expansion of the air inside the tube, so that a strong blast of air rushes through the outlet O of the tube and immediately extinguishes the arc.

By this arrangement, sustained arcing is prevented, as the action of the tube causes the arc to extinguish itself automatically when the current is interrupted.

The porcelain tubes are held in position by the spring K, and the primary of the transformer becomes entirely disconnected from the circuit when the tubes are lifted out.

This form of construction enables the lineman to detach the tubes from the fuse box, and insert the fuse at his convenience. Furthermore, when inserting a fuse in a short circuited line, he does not run the risk of being hurt, as the heated vapor of the exploding fuse can escape through the outlet provided for that purpose, and in a predetermined direction.

The method of attaching the lid not only permits of quick access to the interior of the box, but enables the lineman to tighten the joints by means of the thumb screws L, L, so as to keep the box waterproof.

Fig. 1,978.—Diagram illustrating connections and principles of auto-transformers as explained in the accompanying text.