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Page 211

| Figure 11-12 Door fuse cut-out: (A) Open door indicating fuse has blown, and (B) dropped cartridge indicating fuse has blown. |

| higher interrupting rating than a single-venting tube. In this type, one end (usually the top) remains completely closed during low pressures caused by low fault currents. When high fault currents produce large gas pressures, the top cap is blown off and the expulsion tube vents at both ends. Thus, on low fault currents, the tube is single-venting, and on high fault currents, it is double-venting. |

| De-ion Fuse. |

| In this type of fuse, the fusible element is attached to an internal arcing rod, and both are held under tension by a spring (Fig. 11-14 on page 213). When the fuse melts, the arcing rod is pulled up by the spring, drawing the arc through a sectionalized chamber and breaking it into a series of small arcs. The section of this fuse are also filled with powdered boric acid; as previously mentioned, boric acid forms steam that tends to quench the arc. Since the end of the fuse is open, the pressure of the steam and gases developed during the operation is vented safely. |

| Fuses as Disconnects |

| Fuses often form a part of the disconnecting switch equipment, sometimes arranged as the blade of the switch and sometimes attached to auxiliary clips mounted on the same base (see Chap. 10). |

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