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Page 201

| Figure 11-2 Typical time-current curves for a 10-k link. (Courtesy, McGraw-Edison Co.) |

| malfunction be restricted to the smallest practical section of the system for the shortest time. Systems, therefore, are divided into smaller sections, the number and size of each of the sections being determined by its importance and general economic considerations. |

| Each of the sections may be protected by an interrupting device that operates to de-energize that section before the short circuit or fault occurring within it can affect the rest of the system. The number and type of interrupting devices depend on several factors: the system voltage, usual load current, maximum possible fault current, number of branches, lengths of the sections, the equipment connected to the lines in each of them, and other local or particular conditions. The locations of these protective interrupting devices, known as coordinating points, are usually key points and frequently at the branch intersections. If two or more such devices are installed in a circuit, it is essential for them to be coordinated so that only the section in trouble is de-energized. Needless to say, these devices must be of the correct rating for carrying the normal load current and for responding properly to likely faults. |

| Although these protective devices could be circuit breakers or reclosers, economics generally dictates that many of them be the less expensive fuses. In |

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