This guideline has been prepared to assist the homeowner in complying with the requirements of the National and local codes. This guide is not all-inclusive and will not assure the installation of a safe and reliable electrical system, but may help you make some decisions. Along with meeting The National Electrical Code (NEC) requirements, you must comply with local codes. These include State requirements as well as any applicable County, City or Power Company requirements.
Prior experience, or the time and patience to learn about the electrical trade is necessary. This is a task that not just anyone may be willing to commit to. Even with knowledge and experience, an up to date copy of the National Electrical Code as well as any local codes is a necessity. I applaud the homeowner who has the determination to accomplish this undertaking but here is a word of caution. If your only motivation is saving money, many times I see do-it-yourselfers spend more than they would spend just hiring a reputable professional to begin with. Any good electrician can give you a list of reasons this may be true.
Electrical permits that are normally required for the construction of a new home include-
a. The temporary construction service (if temporary power is necessary),
b. At least one rough-inspection for the wiring of the home.
c. A final inspection.
d. An electrical inspection for the HVAC system.
If you have a pump or well contractor install a pump or well, the installer is required to take out an electrical permit for the pump or well and call for the required inspections for their installation. The same guideline goes for any additional contractors that may be doing any type of electrical installations. (They may not operate on the homeowners permit or another contractors permit).
If for some reason the job does not meet the requirements of the NEC and an extra visit is necessary, an additional re-inspection fee is required before the inspector will return.
The service equipment must be large enough to supply the connected load, which is calculated using Article 220 of the NEC. The most common sizes of residential service equipment are 100, 125, 150, 175 and 200 amperes. The minimum wire size for service entrance conductors are listed below:
THREE WIRE, SINGLE PHASE DWELLING SERVICES
Conductor Types and Sizes
RH-RHH-RHW-THHW-THW-THWN-THHN-XHHW-USE
Type "USE" (Underground Service Entrance) conductors used as service laterals are not permitted to enter a building unless they are triple rated with the additional markings RHH and RHW.
AMPACITY TABLE FOR RESIDENTIAL DWELLING SERVICES
ONLY
|
Copper
|
Aluminum and copper clad Aluminum |
Service rating in amps |
|
AWG |
AWG |
|
|
4 |
2 |
100 |
|
3 |
1 |
110 |
|
2 |
1/0 |
125 |
|
1 |
2/0 |
150 |
|
1/0 |
3/0 |
175 |
|
2/0 |
4/0 |
200 |
|
3/0 |
250 kcmil |
225 |
FOR SERVICES OVER 225 AMPERES REFER TO TABLES IN THE NEC
The service equipment must be grounded in accordance with Article 250 of the NEC, which, in general, says that the neutral must be bonded to the service enclosure and the grounding electrode system as defined in NEC Article 250.50.
The main service equipment panel shall be mounted either outside or inside the dwelling at the point of entrance of the service conductors to the building. All service equipment and electrical panels shall have a clear area 30" wide and 36" deep in front. This clear area must extend from floor to ceiling with no intrusions from other equipment, cabinets, counters, appliances, pipes, etc. Panels are NOT allowed in clothes closets or bathrooms.
In the main service equipment, the neutral and equipment grounding conductors are bonded together; in sub-panels, the neutral is isolated from ground.
BRANCH CIRCUIT WIRING
It is important to note that if you begin a circuit with #12, you must use this same wire size throughout, you CANNOT mix different wire sizes on the same branch circuit.
When Type NM cable is installed parallel to framing members, or in bored holes, it shall be located at least 1¼" from the nearest edge of the framing member, where nails or screws may penetrate the cables. If this distance cannot be maintained, the cable shall be protected by a steel plate or sleeve at least 1/16" thick. Section 300.4 (A), NEC.
Cable or raceway-type wiring methods installed in a groove, to be covered by wallboard, siding, paneling, carpeting, or similar finish, shall be protected by 1/16-inch steel plate, sleeve, or equivalent, or must be recessed in the groove 1 1/4-inch for the full length of the groove in which the cable or raceway is installed. Exception: Raceways as covered in articles 342, 344, 352, and 358. Section 300.4 (E), NEC.
Ceiling mounted paddle fans weighing 35 pounds or less may be supported by outlet boxes identified for such use. Fans weighing more than 35 pounds must be supported independently of the box (422.18), NEC.
REQUIRED BRANCH
CIRCUITS
(a) Small Appliance Branch Circuits - The NEC requires a minimum of two 20-ampere branch circuits to feed receptacle outlets for small appliance loads, including refrigeration equipment in the kitchen, pantry, breakfast room, and dining room. These circuits, whether two or more are used, shall NOT supply anything other than receptacles in these areas. Lighting outlets and built-in appliances such as garbage disposals, hood fans, dishwashers, and trash compactors are NOT permitted on these circuits. Kitchen counter top receptacles must be supplied by at least two small appliance branch circuits.
(b) Laundry Branch Circuit - One 20-amp branch circuit must be provided for the laundry. This circuit is limited to receptacles within the laundry room. No other outlets are permitted on this circuit.
(c) Bathroom Receptacles - At least one 20-amp circuit for bathroom receptacle outlets shall be supplied, such circuits may have no other outlets.
Exception: Where the 20-ampere circuit supplies a single bathroom, outlets for other equipment within the same bathroom shall be permitted to be supplied in accordance with 210.23(A). This circuit would NOT be used to supply a whirlpool bath or a hot tub!
(d) Central Heat - Central heating equipment shall be supplied by an individual branch circuit.
(e) General Lighting Branch Circuits - Shall be computed on a three watts per square foot basis. You may wire up to 600 square feet of living area on a 15 ampere branch circuit or up to 800 square feet on a 20-ampere circuit. These branch circuits may supply lighting outlets in all areas of the dwelling and receptacle outlets, other than those covered in (a) - (d) above.
(f) NOTE: All branch circuits that supply 125 volt, 15- and 20- ampere outlets installed in dwelling unit bedrooms shall be protected by an arc-fault circuit interrupter listed to provide protection of the entire branch circuit. This includes wiring to the smoke detector outlets.210.12, NEC
REQUIRED
RECEPTACLE OUTLETS
(a) At least one outlet shall be installed in bathrooms within 36 inches of the outside edge of each basin. The receptacle outlet shall be located on a wall that is adjacent to the basin location.
(b) At least one outlet in every attached garage, and one outlet in every detached garage with electric power
(c) At least two outlets installed outdoors, one on the front and one on the back of the dwelling, accessible at grade level weatherproof whether or not the attachment plug cap is inserted. Outdoor outlets installed in wet locations shall have an enclosure that is weatherproof whether or not the attachment plug cap is inserted.
(d) At least one receptacle must be installed in the each unfinished portion of the basement. This receptacle is in addition to any receptacles that may be installed for laundry or other specific purposes.
(e) In every kitchen, family room, dining room, living room, parlor, library, den, sun room, bedroom, recreation room or similar room, or area of dwelling units, receptacle outlets shall be installed so that no point along the floor line in any wall space is more than six feet horizontally, measured from an outlet in that space, including any wall space, two feet or more in width, and excluding only that space occupied by sliding panels in exterior walls. The wall space afforded by fixed room dividers, such as freestanding bar-type counters, or railings, shall be included in the six-foot measurement. No outlets may be installed over an electric baseboard heater.
(f) In kitchens and dining areas, a receptacle outlet shall be installed at each counter space wider than 12". Countertop receptacles shall be installed so that no point along the wall line is more than 24" measured horizontally from a receptacle outlet in that space. Peninsular bars and islands 12" or wider shall have at least one receptacle.
Exception: Tennessee Code in dwelling unit’s section states, “The installation of receptacles for island counter spaces and peninsular counter spaces below the countertop shall be optional.
(g) Receptacles installed in the floor must use a box-receptacle combination designed specifically for that purpose. Receptacles installed in the floor within 18" of the wall may be used in place of wall-mounted receptacles.
(h) A receptacle outlet is required in any dwelling unit hallway that is ten feet or more in length.
(i) At least one 15 or 20 ampere, 125 volt GFCI protected receptacle must be installed at an indoor spa or hot tub location, not closer than five feet from the inside wall of the unit and not more than ten feet away from it. Light fixtures, outlets and ceiling fans over spas and hot tubs shall be a minimum of 7'6" above the maximum water level. Outdoors spa or hot tubs have the same requirements as a swimming pool. Check in section 680 of the NEC for those requirements.
(j) A 125 volt, 15- or 20- ampere receptacle outlet shall be installed at an accessible location for the servicing of heating, air-conditioning, and refrigeration equipment. This outlet shall be located on the same level and within 25 feet of the equipment. This includes rooftop-mounted equipment.
(a) At least one wall switch-controlled lighting outlet shall be installed in every habitable room: in bathrooms, hallways, stairways, attached garages, detached garages with electric power, and at outdoor entrances or exits. The lighting outlet for interior stairways shall have a wall switch at each floor level where the difference between floor levels is six steps or more.
(b) At least one wall switch controlled lighting outlet shall be installed in an attic, under-floor space, utility room, and basement, where these spaces are used for storage or contain equipment requiring servicing. The switch shall be located at the point of entry to these areas, and the lighting outlet located at or near the equipment requiring servicing.
GROUND FAULT
PROTECTION
A ground fault circuit interrupter must protect ALL receptacles listed below:
(a) Bathroom receptacles.
(b) All outdoor receptacles.
(c) Garage receptacles, except those not readily accessible such as ceiling mounted receptacles, or single receptacles in dedicated spaces for appliances.
(d) Kitchen receptacles that serve counter top surfaces
(e) Counter top receptacles within 6 feet of a wet bar sink.
(f) All receptacles in an unfinished basement with these exceptions:
(1) Single receptacle within a dedicated location and identified for specific use by a cord and plug connected appliance.
(2) Single receptacle serving a permanently installed sump pump.
(g) All receptacles in crawl spaces at or below grade.
(h) Hydro massage bathtubs.
(i) Spas and Hot tubs and associated electrical components.
Disconnects are required in sight of the following equipment: Look up each in the NEC
(a) Electric water heaters.
(b) Well pump controllers.
(c) Central heating equipment (furnaces, boilers).
(d) Spas and hot tubs.
(e) Hydro massage bathtubs.
(f) Appliances.
Outlet and junction boxes shall be of sufficient size to provide free space for all conductors and devices enclosed in the box. All outlet boxes have a specific volume, measured in cubic inches. For example, if you had two #12/2, with ground NM-B cables entering a box with one duplex receptacle, you would need a box with a minimum volume of 15.75 cubic inches. Each #12 that enters the box needs 2.25 cubic inches with the exception of the grounding conductor which requires one 2.25 cubic inch for all of the grounds. Also, each strap containing one or more devices is counted as the equivalent of two conductors; therefore, 2.25 x 7 = 15.75.
#14 - 2 cubic inches #8 - 3 cubic inches
#12 -2.25 cubic inches #6 - 5 cubic inches
#10 -2.5 cubic inches
All equipment grounding conductors must be connected together with solderless pressure connectors such as wire nuts or crimp sleeves, leaving sufficient extra conductor for attachment to the metal box and/or device. When crimp type connectors are used, they must be crimped using the tool recommended by the manufacturer. Please note that ALL metal junction and outlet boxes must be grounded by attaching the equipment grounding conductor out of the NM cable to the metal box using an approved screw or grounding clip. When circuit conductors are made up, six inches of free conductor must be left for use in make-up and for the attachment of devices.
Electric heat may be installed on 15, 20, or 30 amp branch circuits. Listed below is the maximum wattage that may be installed on each size branch circuit. (All circuits are figured at 240 v)
15A - 2,880 watts maximum
20A - 3,840 watts maximum
30A - 5,760 watts maximum
For example, if you are installing baseboard heaters which are rated 250 watts a linear foot, you could install 15 feet on a 20 amp, 240 volt circuit. 250W x 15 = 3,750 watts.
At the time you call for your rough-in inspection, you should have all wire pulled, stapled properly, and all splices made up and ready to accept devices and fixtures. Please DO NOT install any devices or fixtures or cover any wiring under ground, with insulation or wall coverings, i.e., drywall or paneling. All circuits and calculations shall be completed prior to the rough inspection.
All permits must be on sight. The electrical installation should be complete at the time of request. All devices and fixtures installed, service equipment complete, and labeled properly. All wiring shall be free from short circuits, ground faults and open circuits. All light fixtures are required to be grounded along with light switches that are within five feet of a grounded object.
The time factor prohibits your local inspectors ability to answer all questions. In unique situations, after you have exhausted all of your resources, and still cannot find the answer; your local inspector may then make suggestions where to find information. For this information call during office hours. Office hours and phone number will be stamped on your permit.
(This document is a combination of quotes from codes and personal opinion. I am not responsible for inaccuracies or errors).
Good luck on your project.
Thank you, Deputy Electrical Inspector,
State of Tennessee
Gary Gregory