Electrical Receptacles

The electrical outlet into which we plug an electrical cord is technically known as a convenience receptacle (Fig. 31-3). The number of poles (prongs) and wires, and whether they have a separate grounding wire or not, identifies the different types of receptacles. Grounded receptacles are used on standard 15-A or 20-A branch circuits.

An electrical receptacle is defined by the NEC as "a contact device installed at the outlet for the connection of a single attachment plug." This includes common wall outlets and larger, more complex devices. They are known as convenience receptacle outlets, receptacle outlets, or convenience outlets. Technically, the term "wall plug" is the name for the cap on the wire that carries electricity to an appliance—the part on the end of a line cord that is plugged into a wall.

A receptacle is by definition a single contact device. A normal wall convenience receptacle takes two attachment plugs, and is called a duplex convenience receptacle, or duplex convenience outlet. This is commonly shortened to duplex receptacle or duplex outlet.

Receptacles installed on a standard 15-A or 20-A branch circuit must be of the grounding type. Receptacles connected to different voltages, frequencies, or current types (alternating vs. direct current, AC vs. DC) on

Cover plate

Grounding clip connects mounting strap and metal enclosure.

Grounding clip connects mounting strap and metal enclosure.

Figure 31-3 Duplex convenience receptacle.

the same premises must be polarized. Receptacles are typically 20-A, 125 V, but are available from 10 A to 400 A, and from 125V to 600V. Locking, explosion proof, tamper proof, and decorative design receptacles are available. Some units, such as range receptacles, are designed for specific uses. Split-wired receptacles have one outlet that is always energized, and a second controlled by a wall switch. These are sometimes used for a lamp, with the switch near the entrance to the room.

Receptacles are normally mounted between 30 and 46 cm (12-18 in.) above the finished floor. In shops, laboratories, and other spaces with tables against walls, they are mounted at 107 cm (42 in.) above the floor. Receptacles above kitchen counters are mounted 122 cm (4 ft) above the finished floor. In accessible spaces, the Americans with Disabilities Act Accessibility Guidelines (ADAAG) requires a minimum 38 cm (15 in.) height for outlets, with outlets above kitchen counters at 107 cm (42 in.) above the floor. Where work areas are required to be accessible, as in public library carrels and office workstations, the receptacles should be located above the worksurface whenever possible, or alternatively under the front edge of the worksurface. This requires careful planning.

Modern electronic equipment is very sensitive to random, spurious electrical voltages, called electrical noise. Two special receptacles help eliminate electrical noise. One type with built-in surge suppression protects equipment from over-voltage spikes. Other receptacles with an insulated equipment-grounding terminal separating the device ground terminal from the system (raceway) ground eliminate much of the unwanted electrical noise. This latter type is connected to the system ground at the service entrance only, and is identified by an orange triangle on the faceplate.

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