The volume of electrical boxes shall be sufficient for the number of conductors, devices, and cable clamps contained within the box.
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.
Nonmetallic boxes are marked with their cubic inch capacity. Use the following table to calculate the minimum box size: Conductor Size................................14 AWG........12 AWG Each separate insulated wire..............2 in-3............2.25 in-3 All ground wires (combined)................2 in-3............2.25 in-3 For each device (switch/receptacle).....4 in-3............4.4 in-3 All internal cable clamps (combined)....2 in-3...........2.25 in-3
Sample Box Fill Calculation:
Four 14/2 w/ground type NMB cables: 8 insulated wires...................16 cubic inches All ground wires......................2 cubic inches 1 switch.................................4 cubic inches 1 receptacle...........................4 cubic inches All cable clamps (combined)....2 cubic inches Minimum Box Volume...........28 cubic inches
NEC 370-29 Do not conceal junction boxes in walls, ceilings, or non-accessible attics and under-floor areas.
Residential Electrical Code Examples for Junction Boxes
Boxes: Junction, outlet, and lighting 1.Unused openings in boxes and conduit bodies shall be closed. 2003 IRC E3806.4 2.All boxes shall be accessible. NEC 314.29
3.Boxes shall be installed at each conductor splice point, outlet, switch point, junction point, or pull point. NEC 314 4.Non-metallic boxes of rectangular shape (2 1/4 inch x 4 inches) can be used in both walls and ceilings. No clamps necessary if wire is fastened within 8 inches of the box. NEC 314.17
Always contact your local building authority for complete and up to date code information.
Electrical Wiring Video #2
Electrical Wiring Tips for Home Electrical Wiring Projects
Tripping Circuit Breaker, Outlet at a Wall Switch, Light Fixture without a Ground Wire, Help with Home Electrical Wiring Projects.
See more House Wiring Videos from Ask The Electrician:
Perfect for Homeowners, Students, Handyman, Handywomen, and Electricians Includes: Wiring GFCI Outlets Wiring Home Electric Circuits 120 Volt and 240 Volt Outlet Circuits Wiring Light Switches Wiring 3-Wire and 4-Wire Electric Range Wiring 3-Wire and 4-Wire Dryer Cord and Dryer Outlet How to Troubleshoot and Repair Electrical Wiring Wiring Methods for Upgrading Electrical Wiring NEC Codes for Home Electrical Wiring ....and much more.
Questions about Electrical Codes for Junction Boxes
Questions about Residential Electrical Wiring Codes for Boxes
Question from Jan, a Homeowner in Atascadero, California.
Can I install junction boxes in a crawl space?
I’m working in a 1890’s very small house with a single wall. The house needs to be rewired. The crawl and attic areas are accessible. I plan to run the circuit feeds to the receptacles and switches inside surface mount metal Wiremold V 700 boxes etc. I plan to run the feeding circuits in dry crawl space with 2×8 16 OC joist system. Can I use NM #12 wiring for feeders and make wirenut connections inside 4×4 metal J-boxes inside the crawl space? I will be installing the appropriate cable connectors into and out of those J-boxes.
This electrical wiring question came from Jan, a Homeowner in Atascadero , California.
Jan, the electrical code requires that the junction boxes are accessible, therefore your plan should be fine. Be sure to obtain a permit and have your work inspected.
More about Electrical boxes
What To Do With The Ground Wire Where do I attach the ground wire? Grounding Wall Outlets and Light Switches: What to do When there is Nothing to Attach the Ground Wire to, Grounding Wall Outlets and Light Switches, Ground Wires and Ungrounded Fixtures and Boxes, Bonding the Ground Wire.
Splicing 220 Volt Wiring How to Splice 220 Volt Electrical Wiring: Considerations when splicing 220 volt cable wiring in order to make the splice safe, accessible and makes sure the circuit maintains integrity.
Electrical Code and Swimming Pool Light Fixtures GFCI Ground Fault Protection for Swimming Pool Lights: NEC Article 680-20, As described in this electrical question, anyone who enters the pool with this light on is in Danger of Potential Electrical Shock!
Electrical Code for BX Cable Robert in New York asks; Where in the NEC code book does it show where and how BX can be exposed and what are the restrictions.
electrical boxes - 1691
Electrical Wiring Codes
Electrical Project Skill Level:
Intermediate to Advanced - Best performed by a Certified Electrician or Licensed Electrical Contractor.
Electrical Tools Required:
Basic Electricians Pouch of Hand Tools, Battery Tools, Electric Power Tools, Electrical Meters and Voltage Testers.
Depends on personal level of working capabilities and electrical experience, electrical certification or contractors license, ability to work with tools, install electrical circuit wiring, and the available access to the project area. Electrical Safety:
Identify the electric panel circuits found in the project area, turn them OFF and Tag them with a Note before working with the electrical wiring.
Electrical Wiring Parts and Materials:
Electrical parts and materials for all electrical projects should be approved for the specific project and compliant with local and national electrical codes.
Electrical Codes and Inspections:
Installing additional electrical circuits or wiring should be done according to local and national electrical codes with a permit and be inspected.
This is a testing tool that is a Non-contact tester that I use to easily Detect Voltage in Cables, Cords, Circuit Breakers, Lighting Fixtures, Switches, Outlets and Wires. Simply insert the end of the tester into an outlet, lamp socket, or hold the end of the tester against the wire you wish to test. Very handy and easy to use.
This is great to troubleshoot a problem with outlet circuit wiring, is also used by most inspectors to test for power and check the polarity of circuit wiring.
It detects probable improper wiring conditions in standard 110-125 VAC outlets
Provides 6 probable wiring conditions that are quick and easy to read for ultimate efficiency
Lights indicate if wiring is correct and indicator light chart is included
Tests standard 3-wire outlets UL Listed Light indicates if wiring is incorrect, Very handy and easy to use.
A wire stripping tool used to safely strip electrical wires.
This handy tool has multiple uses:
The wire gauges are shown on the side of the tool so you know which slot to use for stripping insulation.
The end of the tool can be used to grip and bend wire which is handy for attaching wire onto the screw terminals of switches and outlets.
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