You're asking a good and nuanced question about electrical code and best practices when securing electrical boxes. Here's a breakdown of the issues

Key Concerns with Securing Boxes

1. Listing and Labeling (UL, ETL, etc.)

Electrical boxes are "listed" products. This means they have been tested and approved by a recognized testing laboratory (like UL, ETL, CSA, etc.) for specific uses, including how they should be mounted.2.

Manufacturer's Instructions

The listing requires that the box be installed according to the manufacturer's instructions. This is the most important point. The instructions will specify: What types of fasteners are allowed (screw size, material, etc.). Where those fasteners can be placed (pre-drilled holes, knockouts, etc.). How many fasteners are required. Maximum box fill (amount of wires and devices in box) to prevent physical damage to conductors or screws.3.

Structural Integrity

The box needs to be securely fastened so it doesn't come loose, which could create a hazard. The fasteners must be appropriate for the weight of the box, the wires inside, and any devices attached to it.4.

Field Modifications

NEC 110.3(B) states, “Equipment that is listed, labeled, or identified shall be installed and used in accordance with any instructions included in the listing, labeling, or identification.”NEC 110.3(B) states, “Equipment that is listed, labeled, or identified shall be installed and used in accordance with any instructions included in the listing, labeling, or identification.”

Addressing Your Specific Questions Sharp vs. Blunt Screws

The sharpness of the screw isn't the primary concern. The primary concern is the screw's suitability for the material of the box and the material it's being attached to (stud). Sharp screws are typically more appropriate for wood studs. Blunt screws are typically for metal studs. Screws must be sufficient to hold the box in place securely.

Field-Installed Holes



General Rule

Drilling any hole in a listed electrical box can void the listing unless the manufacturer's instructions specifically allow for field-drilled holes and specify the size and location of those holes.

Existing Holes

Most electrical boxes have pre-made holes designed for mounting. Using these holes is generally acceptable. These may include knockouts or designated screw holes.

Side of Box

Drilling a hole in the side of the box definitely risks violating the listing. Most boxes are not designed to be mounted this way, and it could weaken the box.

Screws Not Part of Box Assembly/Instructions

This is where it gets tricky.

If the manufacturer's instructions don't specify a particular screw type, and you use a screw that's appropriate for the materials (e.g., sharp wood screws for wood studs) and doesn't damage the box or create a hazardous condition, it's likely to be acceptable, especially if you are using pre-existing mounting holes. However, some inspectors are very strict and may insist that you only use fasteners specifically listed for use with that box (if such a thing exists).

Potential Code Violations



NEC 110.3(B)

Using a box in a manner not consistent with its listing and manufacturer's instructions.

NEC 314.23

Covers the secure mounting of boxes. This section requires boxes to be supported independently of the raceway (conduit or cable) that enters them.

Recommendations


Read the Instructions

Always start by reading the instructions that come with the electrical box.2.

Use Designated Mounting Holes

If the box has pre-made holes, use those.3.

Choose Appropriate Fasteners

Use screws that are the correct size and material for the box and the mounting surface. For wood studs, a sharp wood screw is generally a good choice.4.

Consult the Inspector (If in Doubt)

If you're unsure about the proper mounting method, ask your local electrical inspector. They have the final say on what's acceptable in your jurisdiction. It's better to ask beforehand than to have to redo the work.5.

Document Your Choices

Keep records of the box manufacturer, model number, and any instructions. This can be helpful if you need to justify your installation to an inspector.6.

Don't Over-Tighten

Avoid over-tightening screws, as this can strip the holes in the box or damage the box itself.

In summary: While sharp wood screws used in pre-existing mounting holes are often acceptable for attaching a box to a wooden stud, it's crucial to prioritize the manufacturer's instructions and local code requirements. When in doubt, consult with a qualified electrician or your local electrical inspector. Flag for review