2005 Residential Electrical Wiring Guide
Previous Electrical Code (Effective June 1, 2005 thru July 31, 2008)
2005 Edition of the National Electrical Code (NEC) wiring guide below:
In order to wire your own home, you must comply with the requirements of the 2005 edition of the National Electrical Code (NEC). The NEC is not intended as a design specification nor an instruction manual for untrained persons, its purpose is the practical safeguarding of persons and property from hazards arising from the use of electricity. This guideline is written to help the lay person comply with the NEC requirements for single family dwelling units, and is in no way inclusive of all requirements for every installation. Caution!! Some locally sold wiring materials may not meet the requirements of the NEC.
Along with meeting NEC requirements, the permit and inspection process defined in Colorado Revised Statutes must be followed. In general, two electrical permits are required for the construction of a new home, one for the construction meter, and another for the wiring of the home. However, the construction meter and wiring can be on the same permit. The electrical inspector will make two inspection visits on a residential permit, one for the rough-in, and one for the final inspection. 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 may be required before the inspector will return.
On this page:
Branch Circuit Wiring
Required Branch Circuits
Required Receptacle Outlets
Required G.F.C.I. Outlets
Equipment Grounding and Conductor Make-up
To Figure Minimum General Lighting/Outlet
Electric Heat Circuitry
Notice: Temporary Meters
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 size wire for service entrance conductors are listed below:
Three Wire, Single Phase Dwelling Services
Conductor Types and Sizes
RHW - THWN - THHN - XHHW - USE
Note: Public Service will not provide meter housings for residential use. Meter housings used must be on Public Service Company approval list.
||Aluminum & Copper-Clad AL
||Service Rating In Amps|
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 defined in 250-28, 250-50, 250-52, 250-53 (New construction 250.2 (A)(3) concrete-encased electrode is required and needs to be inspected).
The main service equipment panel shall be mounted either outside or inside the dwelling as near as possible to 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, etc. Panels are not allowed in clothes closets or bathrooms..
In service equipment the neutral and equipment grounding conductors are bonded together. Note: In sub-panels the neutral is isolated from ground.
2. Branch Circuit Wiring
Type NMB cable (a.k.a. romex) is the most widely used wiring method used in residential dwellings. NM cable must have 90 degree conductor insulation rating which is designated on the cable sheath by a "B". Type N.M.-B, #12, and #14 shall be used for lighting and receptacle circuits, while #10/2 is commonly used for electric water heaters, #10/3 with ground for electrical dryers and cooktops, and #8/3 with ground and #6/3 with ground for ranges and wall mounted ovens. Type "SER" or any four wire cable is required for electrical ranges, cooktops, wall overs and clothes dryers.
These cables must be protected by overcurrent devices (circuit breakers) which do not exceed their rated ampacity. The rated ampacities for cable types are listed below:
|Copper NM Cable Type
||S.E. and S.E.R. Aluminum Cable|
|15 amperes for #14
||40 amperes for #8|
|20 amperes for #12
||50 amperes for #6|
|30 amperes for #10
|50 amperes for #8
|65 amperes for #6
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.
Type NM cable must be stapled within 12" of metal boxes, utilizing approved connectors, within 8" of plastic boxes and every 4-1/2 feet thereafter. Proper connectors must be used where NM cable enters metal cabinets or boxes. NM cable must be stapled 1-1/4" back from the nearest edge of the wood member.
3. Required Branch Circuits
(a) Small Appliance Branch Circuits - The NEC requires a minimum of two 20 amp 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, may have only four outlets each and shall not feed anything other than receptacles in these areas. Lighting outlets are not permitted on these 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 lighting outlets are permitted on this circuit.
(c) A furnace requires a dedicated circuit.
(d) Recommended dedicated circuit (to meet Mfg. Warranty if required) disposal, dishwasher, microwave, and freezer.
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
4. Required Receptacle Outlets
(a) G.FC.I. receptacles, in bathrooms, must be on a 20 amp. circuit and have no other outlets.
(b) At least one in every attached garage, and one in every detached garage with electric power.
(c) At least one installed outdoors (required in the front and back of house) not more than 6'- 6" above grade.
(d) At least one receptacle must be installed in each unfinished basement. All outlets in unfinished basements and unfinished basement areas must be G.F.C.I.
(e) In every kitchen, family room, dining room, living room, parlor, library, den, sunroom, bedroom, recreation room, or similar rooms 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, measured horizontally, from an outlet in that space including any wall space two feet or more in width and the wall space occupied by sliding panels in exterior walls. The wall space afforded by fixed room dividers, such as free-standing bar-type counters, shall be included in the six foot measurement. No outlet may be installed over electric baseboard heater. Note: Article 210-52(c) (1) Wall counter space. A receptacle outlet shall be installed at each wall counter space 12 inches or wider. Receptacle outlets shall be installed so that no point along the wall line is more than 24 inches measured horizontally from a receptacle outlet in that space. (See item 5-(d) below.) At least one receptacle outlet is required at kitchen islands and peninsulas.
5. Required G.F.C.I. Outlets
All receptacles listed below must be protected by a Ground Fault Circuit Interrupter:
(a) Bathroom receptacles.
(b) All outdoor receptacles.
(c) Garage receptacles.
(d) All kitchen outlets that serve counter tops, including islands and peninsulas. (see Article 210-8 (6).)
(e) At least one receptacle in a finished or unfinished basement, this receptacle must be identified as G.F.C.I. protected.
(f) G.F.C.I. protection must be within 6' of laundry, utility sink and wet bars.
6. Conductor Fill
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. (See Table 314.16(b) NEC). This volume must be equal to or greater than the cubic inches required for the number of conductors and devices in the box.
|Conductor/Device Box Fill
|each device counts as
|Note: Count only one (the largest) ground wire|
2 - #12-NM-B cables, one duplex receptacle
4 X 2.25 = 9.0 cu. in.
1 X 2.25 = 2.25 cu. in.
1 X 4.50 = 4.5 cu. in.
NOTE: 15.75 cu. in. minimum box size
7. Equipment Grounding and Conductor Make-up
All equipment grounding conductors must be connected together with solder less 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 wire (from face of box) must be left for use in make-up and for the attachment of devices.
8. To Figure Minimum General Lighting/Outlet
Requirements: Reference Table 220-3-b. 1996 N.E.C
One 120 volt 15 amp. circuit per 500 sq.ft.
Each 15 amp. circuit @ 80% = 12 amps @ 1.5 amps
Per light/outlet = maximum 8 allowed
If using a 20 amp. circuit, maximum 10 allowed
9. Electric Heat Circuitry
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 240V.
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).
10. Rough-in Inspection
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 with insulation or wall covering, i.e., drywall or paneling.
11. Final Inspection
The electrical installation should be complete at the time of request including set of permanent meter, 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. All 120 volt circuits shall have power.
Notice: Temporary Meters
Temporary heat meters must be permitted and inspected, are only valid for sixty (60) days from date of issue, and are for construction purposes only. Only three (3) circuits are allowed, one for heat, one for construction power, and one where a well is used and hot water for heating purposes is needed. If heating is electric, all heating circuits and all radiation units must be installed and thermostat operable. If this meter is used for any other purpose or if the building is occupied, the Building Inspection will have the meter removed without prior notice.
No temporary heat meter will be released until the furnace is complete, the flue is capped off (if water heater is not installed), and the rough electric inspections have been made and approved and G.F.C.I. is on laundry circuit.
If you have questions, please contact your electrical inspector at
303-271-8260 between 7:30 - 8:30 a.m. or 4 - 5 p.m. Monday through Friday.
Last Modified: Jul 29, 2011 01:18 PM