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Receptacle Boxes and Cable Installation Code

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Installing electrical boxes and electrical cables are made easy by following these recommended electrical installation codes. Don't just install your electrical wiring haphazardly, do it by the book...the National Electrical Code.

By installing the appropriate electrical boxes in the right manner, you'll have a safe and great looking installation. The electrical cables that run through walls and in and out of electrical boxes must be both supported and installed with adequate lengths for connections in accordance with these code for proper installation and ease of use.

1. Attaching Cables to Studding

In the code book, section 334.30 states that flat cables must be stapled on the flat side of the cable, not on the edge. This provides a tight wire connection to the stud and prevents any damage to the wire sheathing.

2. Cables Entering the Receptacle Box.

When electrical cables route from box to box, you must leave at least 6" of free conductor wiring in the box for connection purposes. In article 300.14, this technique is explained. If wires are too short, it's much too hard to make a connection and in the event that you need to trim off a bit of wire to rewire a switch or outlet, you'll need a few extra inches of usable wire.

3. Securing Cables

Article 334.30 states that cables coming out of the junction boxes should be secured within 12" of the box in all boxes equipped with cable clamps. These cable clamps are not to be removed. In 314.17(C), it i stated that cables must be secured to the receptacle box. Although, in article 314.17(C) exception, nonmetallic boxes have no cable clamps and must have cables supported within 8" of the junction box. In either instance, the wire is secured by wire staples that keep it from moving within the wall cavity.

4. Lighting Fixture Boxes

Lighting fixture boxes must be listed for support of lighting fixtures because of their weight. Typically, these boxes are either round or octagon shaped. You'll find this information in article 314.27(A). Depending on the material these boxes are made of, whether it is to support a light or ceiling fan, you may need to install a special bracket box to help support the weight, much like the case of ceiling fans.

5. Horizontal and Vertical Cable Strapping

In article 334.30 and 334.30(A), vertically run cables must be supported by strapping every 4'6", although horizontally run cables through bored holes need no further support. By securing the cables in this way, the cables are protected from being pinched between the studs and the drywall. The preferred wire staples have metal nails and plastic cross supports, not staples.

6. Steel Plate Protectors

When cables go through bored holes in studs, there are safety factors to consider. To protect wiring from nails and drywall screws, article 300.4 states that steel plates must be provided to protect cables closer than 1¼” from the edge of the wood framing member. This protects the wire when drywall is installed. These should be used in both vertical and horizontal bored hole applications where the metal plates cover the area in front of the hole where the wire runs through.

7. Mounting Boxes

In article 314.20, it is stated that boxes should be mounted flush with the finished surface of the wall. This would be the outer edge of the drywall. To aid in this installation, most boxes come with depth gauges that making installation of boxes easy. Simply align the right depth on the box to match the thickness of the drywall to be installed and you'll have a flush fitting box.

8. Multiple Wire Installation for Cabling

In article 334.80, 338.10(B), 4(A), it states that when 3 or more NM or SE cables are installed in contact without maintaining spacing or pass through the same opening in wood framing members that are to be caulked or sealed, the allowable ampacity of each conductor must be adjusted in accordance with NEC Table 310.15(B)(@)(A).
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