314.23(B)(1) Nails and Screws.

These standard metal boxes have been secured by driving self-tapping screws through the 1/8-inch diameter mounting holes in the side of the box and into the horizontal metal stud. The 1/8 inch holes punched at the factory are near the front of the box.
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These standard metal boxes have been secured by driving self-tapping screws through the 1/8-inch diameter mounting holes in the side of the box and into the horizontal metal stud. The 1/8 inch holes punched at the factory are near the front of the box.

Code Change Summary: Changes were made to the requirements on how boxes are permitted to be secured by nails or screws.

Some junction and device boxes have brackets for mounting while others do not. Most all metal boxes have holes in the sides and back that were punched at the factory. The 1/8 inch holes punched into the sides of most metal boxes are near the front of the box.

In the 2014 NEC, Section 314.23(B)(1) would allow a standard box to be mounted using nails or screws through holes located within 1⁄4 inch of the “back or ends” of the enclosure. Since the holes in the sides of most metal boxes are near the front, many inspectors would not allow them as mounting holes.

In the 2017 NEC, that issue has been corrected and now the intent of the section is clear. The revised text now permits running nails or screws through mounting holes in the back or in a single side of the enclosure.

The last sentence of the code section was added to make it clear that field drilling of mounting holes is subject to the approval of the inspector.

Below is a preview of Article 314. See the actual NEC text at NFPA.ORG for the complete code section. Once there, click on their link to free access to the 2017 NEC edition of NFPA 70.

2014 Code Language:

314.23(B)(1) Nails and Screws. Nails and screws, where used as a fastening means, shall be attached by using brackets on the outside of the enclosure, or they shall pass through the interior within 6 mm (1⁄4 in.) of the back or ends of the enclosure. Screws shall not be permitted to pass through the box unless exposed threads in the box are protected using approved means to avoid abrasion of conductor insulation.

2017 Code Language:

314.23(B)(1) Nails and Screws. Nails and screws, where used as a fastening means, shall secure boxes by using brackets on the outside of the enclosure, or by using mounting holes in the back or in a single side of the enclosure, or they shall pass through the interior within 6 mm (1∕4 in.) of the back or ends of the enclosure. Screws shall not be permitted to pass through the box unless exposed threads in the box are protected using approved means to avoid abrasion of conductor insulation. Mounting holes made in the field shall be approved.

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314.23(B)(1) Nails and Screws.

Below is a Real Question from our Electrical Continuing Education Courses for Electrical License Renewal:

Which of the following is true when installing a metal switch box?

A: Screws can be installed through mounting holes in one side of the box.
B: Screws can be driven through mounting holes in two sides of the box.
C: Mounting screw threads exposed inside a box are permitted without protection.
D: Screws are NOT permitted to be run through holes in the back of the box.
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