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Electrical Codes for Home Electrical Wiring

electrical-codes Summary: Listing of electrical codes for wiring with examples of electrical wiring codes for home electrical wiring.

Electrical Code Definitions for General Home Wiring Projects



Understanding the importance of Proper Wiring Methods, and wiring according to Electrical Codes

NEC 110.12

Wiring Methods boxes

Unused openings in boxes shall be effectively closed. When openings in non-metallic boxes are broken out and not used, the entire box must be replaced.

NEC 110-12 and 370-18 Unused openings in boxes shall be effectively closed. If openings in non-metallic boxes are broken out and not used, the entire box shall be replaced.

NEC 110.14

Wiring Methods for Conductors and Screw Terminal

Only one conductor shall be installed under a terminal screw. In boxes with more than one ground wire, the ground wires shall be spliced with a wire tail or pig tail attached to the grounding terminal screw of the device.

Examples of Electrical Codes for Home Wiring


Code Adoption Information:
The codes shown are examples only and may not be current or accurate for your application or jurisdiction. Contact your local building authority for complete information.
NEC 110.14

Underground Wiring

Wire splicing means for direct burial conductors shall be listed for such use.

NEC 110.14

Electrical Services wire conductors

Listed anti-oxidant compound shall be used on all aluminum conductor terminations, unless product information specifically states that it is not required.

NEC 110.14

Underground Wiring

Underground wiring splicing Wire splicing means for direct burial conductors shall be listed for such use.

NEC 110-14 Only one conductor shall be installed under a terminal screw. In boxes with more than one ground wire, the ground wires shall be spliced with a wire tail, or pig tail attached to the grounding terminal screw.

NEC 110-14 and 300-15

Wire Splices

All splices, including ground wires, shall be made with an approved splice cap or wire nut and shall be made in approved electrical boxes or enclosures.

NEC 200.7(C)

Wiring Methods

wiring Where permanently re-identified at each location where it is
visible and accessible, the conductor with white colored insulation in type NM cable may be used as an ungrounded conductor.

NEC 250-134 and 370-4

Box Covers and Plates

Metal boxes, cover plates, and plaster rings shall be grounded. Switches, including dimmer switches, shall be grounded and shall provide a means to ground metal plates.

NEC 300-3 All conductors of the same circuit, including grounded conductors, shall be contained in the same raceway, cable, or trench.

NEC 300-4 In both exposed and concealed locations, where cables are installed through bored holes in joists, rafters, or wood framing members, the holes shall be bored so that the edge of the hole is not less than 1 1/4 inch from the nearest edge of the wood member. Where this distance cannot be maintained, the cable shall be protected from penetration by screws or nails by a steel plate at least 1/16th inch thick and of appropriate length and width.

NEC 314.4

Wiring Methods Grounding

All electrical equipment, metal boxes, cover plates, and plaster rings shall be grounded. All switches, including dimmer switches, shall be grounded.

NEC 300-14 At all boxes there shall be a minimum wire length of 6 inches, with at least 3 inches outside the box.

NEC 314.17

Wiring Methods Boxes

Unused openings in boxes shall be effectively closed. When openings in non-metallic boxes are broken out and not used, the entire box must be replaced.

NEC 314.17

Wiring Methods Type NM Wire

Outer jacket in box outer jacket of NM cable shall extend into the box a minimum of 1 inch.

NEC 314.19

Wiring Methods Junction Boxes Accessible

Junction boxes shall be installed so that the wiring contained in them can be rendered accessible without removing any part of the building.

NEC 300-22 Type NM cable shall not be installed in spaces used for cold air returns, however NM is permitted to pass through perpendicular to the long dimension of such spaces.

NEC 314.23

Wiring Methods for Boxes

All electrical boxes shall be rigidly secured to the building structure.

NEC 314.25

Wiring Methods Lighting Boxes

In completed installations, each box shall have a lamp-holder, canopy or device with an appropriate cover plate.

NEC 314.27

Wiring Methods Ceiling Fan Boxes

When boxes are used as the sole support for a ceiling paddle fan, they shall be listed and labeled for such use

NEC 334.3

Wiring Methods Type NM Wire Support

Type NM (nonmetallic) cable shall be secured at intervals not exceeding 1.4 m [4.5'] and within 300 mm [12inches] of each box.

NEC 336-18 and 370-17 Type NM (nonmetallic) cable shall be secured at intervals not exceeding 4 1/2 feet and within 12 inches of each box. However, if a single gang device box without a clamp is used, the cable shall be secured within 8 inches of the box.

NEC 370-16 The volume of electrical boxes shall be sufficient for the number of conductors, devices, and cable clamps contained within the box.
Nonmetallic boxes are marked with their cubic inch capacity.

How to Calculate Box Size

Conductor Size 14 gauge 12 gauge
For each separate insulated wire 2 cu in 2.25 cu in
All ground wires (combined) 2 cu in 2.25 cu in
For each device (switch/receptacle) 4 cu in 4.5 cu in
All internal cable clamps (combined) 2 cu in 2.25 cu in

Sample Box Fill Calculation

Four #14/2 with ground cables:
Eight insulated wires 16 cubic inches
All ground wires 2 cubic inches
One switch 4 cubic inches
One receptacle 4 cubic inches
All clamps 2 cubic inches
Total box volume required 28 cubic inches


NEC 370-17 The outer jacket of NM cable shall extend into the box a minimum of 1/4 inch.

NEC 370-23 All electrical boxes shall be securely supported by the building structure.

NEC 370-25 and 410-12In a completed installation, all outlet boxes shall have a cover, canopy for a lighting fixture, or device with an appropriate plate.

NEC 370-27 When boxes are used as the sole support for a ceiling paddle fan, they shall be listed and labeled for such use.

NEC 370-29 Do not conceal junction boxes in walls, ceilings, or non-accessible attics and under-floor areas.

NEC 404.9

Wiring Methods Grounding

All electrical equipment, metal boxes, cover plates, and plaster rings shall be grounded. All switches, including dimmer switches, shall be grounded.

Residential Electrical Code Examples for Wiring

IRC - International Residential Codes

5 Examples of IRC Wiring Methods


  1. Cable and wires installed in grooves or holes in studs or joists that are less that 1- 1/4 inch from the face of the stud or joist shall be protected by 1/16 inch thick steel plates, sleeves, or equivalent. NEC 300.4
  2. Nonmetallic sheathed cable shall be supported every 4.5 feet and within 12 inches of every box. 2003 IRC E3702.1
  3. Wiring is only permitted to travel through the cold-air return and through no other ducts, plenums, or other air handling spaces. NEC 300.22
  4. Switches or circuit breakers shall not disconnect the grounded conductor of a circuit. NEC 404.2 (B)
  5. Maximum bends of conduit shall not exceed 360 degrees total. NEC 352.26
  6. Bends is Romex cable shall be made so the radius of the curve of the inner edge of the bend is not less than 5 times the diameter of the cable. NEC 334.24
  7. Each wire entering a box and terminating or splicing therein is counted as one wire. Interior box clamps all count as one conductor. Each device shall count as two conductors based on the largest conductor connected to it. NEC 314.16
  8. Cord connected, built-in kitchen appliances are allowed, but the receptacle must be accessible without removing the appliance. NEC 422.33
  9. Ceiling fans shall be supported from outlet boxes identified for such use. Fans that exceed 50 pounds shall be supported independently of the box. NEC 314.27
Always contact your local building authority for complete and up to date code information.



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