how to knock out holes in plastic electrical box

3 min read 20-01-2025

how to knock out holes in plastic electrical box

Plastic electrical boxes are a common sight in many homes and buildings. They provide a safe and convenient way to house electrical components. But sometimes, you need to create additional openings for wires or other fittings. This guide will show you how to knock out holes in plastic electrical boxes safely and effectively. Knowing how to do this properly is crucial for a clean, professional, and safe electrical installation.

Assessing Your Box and Choosing the Right Knockout

Before you begin, carefully inspect your electrical box. Identify the location of the pre-marked knockouts. These are usually indicated by a slightly weakened area of plastic, often with a small raised area showing where to punch.

Types of Knockouts

Most plastic electrical boxes come with several pre-installed knockouts of various sizes. Check to see if the box already has a knockout suitable for your needs. If not, you'll need to carefully choose which knockout to remove to best suit your wiring requirements. Removing the wrong knockout could weaken the box's structure.

Tools You'll Need

Knockout punch: This specialized tool is designed for punching out holes in electrical boxes. You can find a variety of knockout punches at most hardware stores and online retailers. Choose one that matches the size of the hole you need. Different punches work with different box materials and knockout sizes.
Screwdriver (optional): A flat-head screwdriver can sometimes assist in starting the knockout process, particularly on stubborn knockouts.
Safety glasses: Always protect your eyes from flying debris.

Step-by-Step Guide to Knocking Out a Hole

1. Prepare the Box: Make sure the electrical box is securely mounted and free from any obstacles. Always turn off the power to the circuit before you begin working. This is a critical safety precaution.

2. Position the Knockout Punch: Firmly place the knockout punch over the pre-marked knockout you intend to remove. Align it precisely to avoid damaging the surrounding plastic.

3. Punch Out the Knockout: Strike the punch firmly and evenly with a hammer. Use controlled, measured blows. Avoid applying excessive force, which might crack the box. If the knockout is stubborn, consider using a screwdriver to slightly loosen it before using the punch.

4. Inspect the Hole: Once the knockout is removed, inspect the hole for any sharp edges or burrs. These could damage wires. If necessary, use a file or sandpaper to smooth any rough areas. Removing burrs prevents wire damage.

5. Complete Your Wiring: Now that you have the hole, carefully feed the wires through. Ensure the wires are properly secured and don't protrude beyond the box.

Tips for a Clean and Safe Job

Start small: If you're unsure, start with a smaller knockout and enlarge it if necessary. It's easier to enlarge a hole than to repair a damaged box.
Use the right tool: A properly sized and maintained knockout punch is essential for a clean cut.
Take your time: Rushing the process can lead to mistakes and damage to the box. Steady, controlled movements are key.
Protect yourself: Always wear safety glasses to protect your eyes from flying debris.

Alternatives to Knocking Out Holes

If you're uncomfortable knocking out holes yourself, or if you need more precision, consider using a hole saw or a rotary tool with a cutting bit. However, these methods require more skill and precision. Improper use can easily damage the box. If you lack experience, using a pre-existing knockout is the best and safest option.

By following these steps and tips, you can safely and efficiently knock out holes in plastic electrical boxes. Remember, safety is paramount, so always turn off the power before working with any electrical components. If you're unsure about any aspect of this process, consult a qualified electrician.