Electrical Design For Residences

Residential electrical requirements are set by NFPA 70A, ^ Electrical Code for One & Two Family Dwellings, which sets the distances for electrical outlets and mandates the use of GFCIs in wet locations. Electrical outlets are not permitted directly above baseboard heating units in newer buildings. Ranges and ovens, open-top gas broiler units, clothes dryers, and water heaters have their own specific code requirements or standards.

Electrical codes require that every room, hallway, stairway, attached garage, and outdoor entrance must have a minimum of one lighting outlet controlled by a wall switch. In rooms other than the kitchen and bath room, the wall switch can control one or more receptacles for plugging in lamps rather than actual lighting outlets for ceiling- or wall-mounted lights. One lighting outlet of any type is required in each utility room, attic, basement, or underfloor space that is used for storage or that contains equipment that may require service.

The number of branch circuits required for a residence, including an allowance for expansion, is estimated by allotting one 15-A circuit per 37 to 45 square meters (400-480 square ft), or one 20-A circuit per 49 to 60 square meters (530-640 square ft) plus an allowance for expansion, with more provided as needed.

No point on a wall is permitted to be more than 1.8 meters (6 ft) from a 20-A, grounding-type convenience receptacle. Any wall 61 cm (2 ft) or more in length, including walls broken by fireplaces, must have a receptacle. You must have a receptacle within 1.8 meters (6 ft) of any door or opening, including arches but not including windows. Receptacles should not be combined with switches into a single outlet unless convenience of use dictates that the receptacle should be mounted as high as a switch. In rooms without overhead lights, provide a switch control for one-half of a receptacle intended for a lamp in an appropriate place.

Code requirements are geared to prevent us from running an octopus of appliance cords off an extension cord plugged into a single outlet. Too much power coming through a single extension cord can overheat the cord and cause a fire. The NEC requires a minimum of two 20-A appliance branch circuits exclusively for receptacle outlets for small appliances in the kitchen, pantry, breakfast and/or dining room, and similar areas, considering that any receptacle in these areas is a potential appliance outlet. Clock outlets are allowed on these circuits. All kitchen outlets intended to serve coun-tertop areas are to be fed from at least two of these circuits, so that all countertop outlets are not lost if one circuit fails. According to the NEC, no point on the wall behind the countertop can be more than 61 cm (2 ft) from an outlet, and all countertop convenience receptacles must be GFCI types. Every counter space greater than 30 cm (1 ft) in length should have a receptacle (Fig. 29-5). With a maximum of four receptacle outlets per 20-A circuit, and an ever-increasing variety of small electrical appliances, you usually need more than two appliance circuits in the kitchen.

Dishwashers, microwaves, refrigerators, and garbage disposals each require their own separate 20-amp circuit. An electric range or oven requires an individual 50-A, 120/240V major appliance circuit. Gas appliances also require their own separate fuel lines. Receptacles behind stationary appliances like refrigerators do not count toward the 3.66-meter (12-ft) spacing requirement. Plan for a readily accessible means for disconnecting electric ranges, cooktops, and ovens within sight of these appliances. A small kitchen panel recessed into

Figure 29-5 Typical kitchen power plan.

Range and oven outlet boxes wall mounted 36" AFF, flexible connection to units.

Dishwasher receptacle on wall behind unit, 6" above floor

Countertop appliance receptacles wall mounted 2" above backsplash

Switch & outlet for exhaust fan

Oven & Range

Oven & Range

Switch & outlet for exhaust fan

Dishwasher

Refrigerator

Countertop appliance receptacle

Refrigerator

Countertop appliance receptacle

Electrical panel the kitchen wall to control and disconnect kitchen appliances is a good idea.

In bathrooms, locate electrical switches and convenience outlets wherever needed, but away from water and wet areas. They must not be accessible from the tub or shower. All bathroom outlets should be GFCI types. Supply a minimum of one 20-A wall-mounted GFCI receptacle adjacent to the bathroom lavatory, fed from a 20-A circuit that feeds only these receptacles. Do not connect the receptacle near the lavatory to the bathroom lighting, exhaust fan, heaters, or other outlets.

Each bedroom in a house without central air-conditioning needs one additional circuit, similar to an appliance circuit, for use with a window air conditioner. Locate a pair of duplex outlets, two on each side of the bed, for clocks, radios, lamps, and electric blankets. For closets, switch controls are preferable to pull-chains, which are a nuisance but considerably cheaper.

To accommodate home offices, each study and workroom or large master bedroom should be equipped electrically to double as an office. At a minimum, allow six duplex 15- or 20-A receptacles on a minimum of two different circuits, one of which serves no other outlets, and all of which have adequate surge protection. An additional separate insulated and isolated ground wire, connected only at the service entrance, should run to boxes containing two of these receptacles, where it should be terminated, clearly marked, and labeled. This will allow special grounding receptacles if the normal receptacles have too much electrical noise for computer use. Install two phone jacks in recessed boxes, with an empty 19-mm (f-in.) conduit from the telephone entry service point to an empty 100-mm (4-in.) square box. The incoming telephone service lines need a surge suppressor.

The NEC requires a minimum of one 20-A appliance circuit exclusively for laundry outlets. In addition, an individual 30-A, 120/240V major appliance circuit, separate from the laundry circuit and rated for an electric dryer, must be supplied along with a heavy duty receptacle, unless it is certain that a gas dryer will be used.

Places that are often used for workshop-type activities, like garages, utility rooms, and basements, should have receptacles in appliance-type circuits, with a maximum of four receptacles per circuit. Basements are required to have a minimum of one receptacle. Receptacles in garages, sheds, crawl spaces, be-low-grade finished or unfinished basements, or outdoors must be GFCI types. GFCI-protected and weatherproofed receptacles must be located on the front and on the rear of the house, with a switch controlling them inside the house.

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