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Page 217

| may be filled with solids, such as sand or boric acid (Fig. 11-8), or with liquids (Fig. 11-7), such as fire extinguishing liquids (carbon tetrachloride, for example); high duty fuses may be filled with oil (Fig. 11-9). |

| 5. Expulsion-type fuses are designed so that the gases formed by the vaporizing of the fuse and the expansion of the surrounding air and filler material act to blow out the arc (Fig. 11-10). In another de-ion type, the arc is drawn over a grid so that it breaks up into smaller arcs more readily extinguished (Fig. 11-14). |

| 6. Fuses may act singly (and also serve as disconnects), and may be mounted together to furnish a three-shot fuse (Fig. 11-15), arranged so that if the first fuse blows, the second automatically takes its place, and should this blow, a third takes its place. When all three have blown, the line or equipment is de-energized. |

| STUDY QUESTIONS |

| 1. What is the function of a fuse? |

| 2. Name several types of fuses and where they are used. |

| 3. Of what are fuses made? |

| 4. What is meant by the time-clearing characteristic of a fuse? |

| 5. What is meant by fuse coordination? |

| 6. What is an expulsion fuse? Where is it generally used? What is meant by double venting? |

| 7. What is a de-ion fuse? How does it function? |

| 8. What is a fuse cut-out? |

| 9. What is a three-shot fuse? Where is it used? |

| 10. What considerations should be taken into account in the selection of fuses and their mountings? |

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