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Page 152

| Types of Indoor and Outdoor Breakers |

| Station or Indoor Types |

| Small, automatically operated breakers are used indoors whenever very large currents are not involved. These may be either air or oil breakers suitable for manual or electrical operation, with a usual maximum voltage of 15,000 V. |

| Larger automatically operated breakers having a high interrupt capacity may be constructed as single-pole or multipole units. The multipole units may be made up of single-pole units or may have all poles supported on a common frame in a single tank. Because of the heavy short-circuit currents that breakers of this type are called upon to interrupt, considerable amounts of oil vapor or gas may be generated. The tanks are usually provided with mufflers to relieve the pressure and condense the gases and thus prevent escape of the oil (commonly called throwing of oil). Oil leakage is taken care of by means of drains (to safe holding areas) installed in the floors; the area containing the breakers may be encompassed by dams or curbs to form a basin that will contain any oil that flows from a breaker in trouble. |

| These larger breakers are electrically and fully automatically operated. They may be mounted on trucks or on structural steel frames. |

| Outdoor Types |

| Since outdoor oil circuit breakers are designed to withstand weather conditions of all kinds, their live parts usually have greater clearances and their physical dimensions are larger than those for indoor types (which are usually limited to breakers operating at lower voltages and less demanding interrupt duties). They are usually mounted on a self-supporting steel framework. The poles for each breaker are operated through a common shaft actuated by one operating mechanism. Outdoor breakers may also be installed in oil-containing concrete or earth encompassed basins. |

| Metal-Clad Switchgear... |

| For smaller circuit breakers such as those found in industrial plants or in electric utility distribution substations, metal-clad switchgear installed outdoors (as well as indoors) will provide maximum safety to the operator. Since all high-voltage equipment and connections are enclosed in grounded metal compartments, danger from accidental contact is avoided. Access to low-voltage control wiring and secondary connection compartments is provided by hinged doors and panels that may be opened safely when the units are in service because steel barriers isolate these compartments from the high-voltage circuits (Fig. 8-23). Access to high-voltage areasincluding current and potential transformers, busses, connections, and the breaker itselfis |

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