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| Open or Link Fuses |

| The open or link fuse is merely a piece of metal ribbon or fuse wire connected between two terminals. An open-mounted fuse is subject to air currents and will itself cause some movement of air surrounding it as it heats up. The fact that the fuse rating will change as the ambient temperature changes has the effect of decreasing the accuracy of fuse operation. Since open fuses must vaporize metal in their operation, they may smudge or burn surrounding surfaces. Copper-terminal clips are sometimes attached to the fuse strip, which is often also enclosed in insulating boxes of porcelain, asbestos tubes, or other casings of fire-resisting material that confine the explosion and increase the accuracy of operation. These can be readily disassembled and the fuse element replaced. |

| Enclosed Fuses |

| In enclosed fuses, the fuse element is enclosed within a tube of insulating material, such as glass, fiber, or Micarta (Fig. 11-6). For small-capacity fuses at voltages to about 15,000 V, the fuse wire or element is fastened to caps at each end of the casing that are usually made of brass. The tube is filled with a material, usually in powdered form, that acts to absorb the heat and the gases liberated when a fuse is blown. It also acts to condense the vapor of the molten metal and to chill the arc, thereby breaking the continuity of the circuit by filling the gap that is formed when the fuse melts and preventing the arc from restriking. These fuses are usually used with potential transformers or other accessory equipment. |

| Figure 11-6 Assembly of enclosed fuse. |

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