disconnecting the service conductors from the supplysource. It may consist of a single manually operatedswitch or a circuit breaker. The NECsets aminimum size for entrance switches at 60 A for thefuse type and 50A for the circuit breaker type. ACIRCUIT BREAKER is a protective device thatautomatically opens the circuit, rather than burningout like a fuse, when the amperage exceeds that ratedfor the circuit breaker. The NECrecommends aminimum size of 100-A service for individualresidences. However, when not more than two two-wire branch circuits are installed, a 30-A entranceswitch may be used.PanelboardA PANELBOARD (fig. 9-10) is defined by theNECas a single panel, or a group of panel unitsdesignated for assembly in the form of a single panel,including buses. It comes with or without switchesand/or automatic overcurrent protective devices forthe control of light, heat, or power circuits of smallindividual as well as aggregate capacity; it isdesigned to be placed in a cabinet or a cutout box andplaced in or against a wall or partition and is onlyaccessible from the front.A BREAKER PANEL uses a thermal unit builtinto the switch with the breaker being preset at thefactory to open automatically at a predetermined73.11Figure 9-11.-Lighting panel.ampere setting. It maybe reset to the ON positionafter a short cooling-off period.LIGHTING PANELS (fig. 9-11) are normallyequipped with 15-A single-pole automatic circuitbreakers, while the power panels may have one-,two-, or three-pole automatic circuit breakers with acapacity to handle the designated load. In mostbuildings, the entrance switch and panelboards canbe mounted close to each other; however, they mustbe placed where service and maintenance can beeasily performed. They should not block any passagethat is supposed to be open, and they should not be ina place where exposure to corrosive fumes anddampness is imminent. Panelboards should be locatedas near as possible to the center of the electrical load.ConductorsELECTRICAL CONDUCTORS generally consistof drawn copper or aluminum formed into wire. Theyprovide paths for the flow of electrical current.Conductors are usually covered with insulatingmaterials (fig. 9-12) to minimize theFigure 9-12.-Types of single insulatedconductors.9-8
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