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Page 182

| Disconnects are connected in series on both sides of a piece of electrical equipment (including circuit breakers) or at some point or points in an electric supply line. They should never be opened until the oil circuit breaker or air-break switch in the circuit has been opened (Fig. 10-3B). They thus provide a second (and usually visible) physical break in the circuit in the event the breaker or air-break switch is accidentally closed. The disconnect should always be closed before the breaker or air-break switch has been closed to energize the equipment or circuit from which workmen have been cleared. |

| Operating in the same manner, disconnects may also be used to sectionalize circuits when, for example, it is necessary to locate a faulted section of a circuit. They may also be used to transfer loads from one circuit to another when, for example, it is necessary to eliminate or avoid overloading a circuit. |

| Most disconnects or disconnecting switches consist of hinged single or multiple blades and contact clips or receptacles mounted on porcelain or other insulation. Locking devices or latches are sometimes provided to prevent the disconnect blade from opening accidentally or from being blown open during a heavy short-circuit condition. Disconnects may be constructed and installed as single-pole units or as multipole units with all blades operated by a single actuating device. For greater safety, they may be designed to operate with a switch stick made of insulating wood or plastic. In this design, the hook on the end of the stick is placed in the hole or eye at the opening end of the switch blade. |

| Both disconnect and air-break switches that are mounted outdoors at the top of poles or other structures may be designed to operate with such a switch stick. In most cases, however, such switches are located at a considerable height and are operated by a mechanism, a system of linkages actuated by a crank or motor with the control handle at some convenient location near the ground (Fig. 10-4). To avoid unauthorized or erroneous operation, they may be locked in position with one or more special locks capable of being opened only by the correct key or combination in sole possession of authorized personnel. |

| When a disconnect is closed, the switch blades should be rapidly and completely closed into the contact clips or receptacles. Because arcs are usually not formed when switching contacts are closed and held closed, the closing of a de-energized disconnect blade onto an energized clip of the disconnect may be permitted under very special conditions, usually of an emergency nature. In such cases, extraordinary precautions must be taken because of the additional hazards involved. |

| In some types of switch gear, such as metal-clad distribution modules, disconnects are so attached to the sliding breaker structures that they are disconnected from the circuit when the breaker unit is rolled out. Mechanical interlocks prevent the moving of the breaker unit and the disconnects into or out of the operating position unless the breaker is open (Fig. 10-5). |

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