Electrical Panels

The layout of the electrical system starts with the location of the electrical panels (Fig. 28-3). In residences, the service equipment and the building's panel board are combined in one unit. The panel board is usually located in the garage, a utility room, or the basement. It is located as close to major electrical loads as feasi-

Service conductor

Circuit directory

Circuit directory

- Circuit ibreakers

- Panelboard distributes electricity to branch circuits

Figure 28-3 Electrical panel board.

ble, and sometimes an additional subpanel is added near kitchen and laundry loads. In apartments, panels are often located in the kitchen or in a corridor immediately adjacent to the kitchen, where they are used as the code-required means for disconnecting most fixed appliances.

In smaller commercial buildings, electrical panels may be recessed into corridor walls. In small office, retail, and other buildings, lighting panels may be mounted in a convenient area to enable the use of circuit breakers for load switching. Buildings six and more stories high use electrical closets for the panels, and risers to connect floors. Larger buildings use strategically located electrical closets to house all electrical supply equipment.

A switchboard is the main electrical panel that distributes the electricity from the utility service connection to the rest of the building. A switchboard is a large freestanding assembly of switches, fuses, and/or circuit breakers that provides switching and overcurrent protection to a number of circuits connected to a single source. Switchboards often also include metering and other instrumentation. The switchboard distributes bulk power into smaller packages and provides protection for that process. Modern switchboards are all of a type called "deadfront," where all live points, circuit breakers, switches, and fuses are completely enclosed in the metal structure. Pushbuttons and handles on the panel front control the equipment.

The NEC regulates the size of the room that contains a switchboard. When equipment is located on both sides of the room, access space is required on both sides. If the room contains a transformer also, additional space must be allowed. The room must be ventilated either directly to the outside or with ducts and fans. Smaller distribution switchboards do not require a special room, and are usually located in a wire screen enclosure with "Danger—High Voltage" signs. Switchboard rooms require exits, hallways, and hatches large enough for the installation and removal of equipment.

Low-voltage switchboards with large circuit breakers, and all high-voltage (over 600V) equipment are referred to as switchgear. In commercial, industrial, and public buildings, switchgear is usually located in the basement in a separate well-ventilated electrical switchgear room. Switchgear rooms, emergency generator rooms, and transformer vaults must be completely enclosed and must have their own emergency lighting source.

Panelboards are similar to switchboards but on a smaller scale. They accept relatively large blocks of power and distribute smaller blocks of electricity to each floor or tenant space. Within the panelboard, main buses, fuses, or circuit breakers feed smaller branch circuits that contain lighting, motors, and so forth. This equipment is mounted inside an open metal cabinet called a backbox, with prefabricated knockouts at the top, bottom, and sides for connecting conduits carrying circuit conductors. The panelboard may have a main circuit breaker that disconnects the entire panel in the event of a major fault. Small panels in residential work may be referred to as load centers.

One-sided panels are housed in electrical closets or cabinets placed in or against a wall. They are stacked vertically in multistory buildings. Each floor may also have one or more branch panelboards that supply electricity to a particular area or tenant. Additional distribution panels are located as needed by the loads they serve. Self-contained areas, like laboratories, should have their own panels.

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