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Page 209

| Expulsion Fuses |

| In expulsion fuses, open fuse wires are placed in a holder so designed that the expulsion of the gases formed by the vaporizing of the fuse and the expansion of the surrounding air is sufficient to blow out the arc (Fig. 11-10). Strong, heavily insulated tubes are used, sometimes reinforced by a metal end cap where the arcing first occurs. In some types, a fiber cylinder surrounding the fuse element is deliberately placed there so that additional gases formed when the arc attacks the fiber help snuff out the arc. In other types, a spring is attached to the fuse element as a means of drawing the arc apart faster when the fuse blows. Other types employ both of these measures. |

| One of the most popular fuses is the so-called fuse link associated with cut-outs in circuits operating at 15,000 V or below (Fig. 11-11 on page 210). This fuse is made up of three parts: a stranded flexible cable, a fusible link, and a metal button or cap. The button is attached to the top of the fuse link and the cable at the bottom. The fuse fits into an insulating tube made of fiber or Micarta. A cap screwed over the button seals the top end, and the flexible cable is held taut by a spring at the bottom. The arc is blown out of the bottom of the tube, and the spring pulls the fuse out of the tube when it melts. |

| For voltages under 7,500 V, the fuse element is often situated in an enclosed cut-out made of porcelain. The fuse is inserted in contacts fastened to the door. The hinge of the door is at the bottom, and, when the door is closed, the fuse contacts fit into the stationary contacts contained within the porcelain receptacle. For voltages between 7,500 and 15,000 V, the fuse and |

| Figure 11-10 Cross section of typical expulsion fuse. |

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