How to Remove a Knockout from an Electrical Box: A Comprehensive Guide

Removing a knockout from an electrical box is a common task in electrical work, whether you’re installing new wiring, adding outlets, or modifying existing circuits. Knockouts are pre-cut circles in the metal or plastic of the electrical box that can be easily removed to create openings for running electrical conduit or cables. While the process is generally straightforward, it’s crucial to do it safely and correctly to avoid damaging the box or injuring yourself. This comprehensive guide will walk you through the different methods of removing knockouts, along with detailed instructions and safety precautions.

## Understanding Electrical Knockouts

Before diving into the removal process, it’s essential to understand what electrical knockouts are and why they are used.

* **Purpose:** Knockouts allow electricians to easily create entry points into the electrical box for wires and cables. They provide flexibility in wiring configurations, allowing for connections from various directions.
* **Types:** Knockouts come in different sizes to accommodate various conduit and cable sizes. Standard sizes include 1/2 inch, 3/4 inch, 1 inch, and larger.
* **Material:** Electrical boxes are typically made of metal (steel or aluminum) or plastic (PVC). The knockout removal methods can vary slightly depending on the box material.
* **Location:** Knockouts are strategically placed on the sides, top, bottom, and back of the electrical box.

## Safety First: Essential Precautions

Safety should always be your top priority when working with electricity. Before attempting to remove a knockout, take the following precautions:

1. **Turn Off the Power:** The most crucial step is to de-energize the circuit you’ll be working on. Locate the circuit breaker that controls the electrical box and switch it to the “OFF” position. Double-check that the power is off by using a non-contact voltage tester. Touch the tester to the wires near the knockout. If the tester indicates voltage, the power is still on, and you need to identify and turn off the correct breaker.

2. **Wear Safety Glasses:** Protect your eyes from flying debris, especially when working with metal electrical boxes.

3. **Use Insulated Tools:** Use tools with insulated handles to prevent electrical shock. Even with the power off, there’s always a chance of encountering stray voltage.

4. **Wear Gloves:** Wearing work gloves provides a better grip and protects your hands from sharp edges on metal knockouts.

5. **Inspect the Box:** Before starting, inspect the electrical box for any signs of damage, such as cracks, rust, or corrosion. If the box is damaged, it should be replaced rather than repaired.

6. **When in doubt, Hire a Qualified Electrician:** If you are not comfortable working with electricity, or if you have any doubts about your ability to safely remove a knockout, it is best to hire a qualified electrician. Electricity can be dangerous, and it is important to take all necessary precautions to protect yourself and others.

## Tools You’ll Need

The tools required for removing a knockout will depend on the type of electrical box (metal or plastic) and the preferred method. Here’s a list of common tools you might need:

* **Screwdriver (Flathead and/or Phillips):** Used for prying or levering out knockouts, especially on plastic boxes.
* **Hammer:** Used to tap or drive a screwdriver or punch.
* **Punch and Hammer (for metal boxes):** A specialized tool for cleanly knocking out metal knockouts.
* **Pliers (Channel-Lock or Regular):** Used for gripping and twisting knockouts.
* **Metal File or Deburring Tool:** Used to smooth sharp edges on metal boxes after removing the knockout.
* **Utility Knife:** For scoring plastic boxes around the knockout before prying.
* **Knockout Punch Set (Optional but Recommended for Larger Sizes):** A tool that uses a bolt and die to cleanly punch out knockouts of various sizes, especially useful for larger conduit sizes.
* **Non-Contact Voltage Tester:** To verify that the power is off.
* **Safety Glasses:** To protect your eyes.
* **Work Gloves:** To protect your hands.

## Methods for Removing Knockouts

Here are several methods for removing knockouts from electrical boxes, starting with the simplest and most common:

### 1. Using a Screwdriver and Hammer (for Metal Boxes)

This is a standard method for removing knockouts from metal electrical boxes. It’s effective but can sometimes leave a slightly jagged edge, which will require filing.

**Steps:**

1. **Position the Screwdriver:** Place the tip of a flathead screwdriver on the inside edge of the knockout, at an angle.
2. **Tap with Hammer:** Gently tap the end of the screwdriver with a hammer. The goal is to start bending the knockout inward.
3. **Move Around the Knockout:** Reposition the screwdriver to a different point on the knockout’s edge, and repeat the tapping. Work your way around the entire circumference of the knockout.
4. **Increase Force (if needed):** As you work your way around, you can gradually increase the force of your hammer blows. The knockout should start to loosen and bend inward.
5. **Remove the Knockout:** Once the knockout is sufficiently bent, you should be able to pry it out completely with the screwdriver or pliers. If it’s stubborn, continue tapping and bending.
6. **Deburr the Edge:** After removing the knockout, use a metal file or deburring tool to smooth any sharp edges around the opening. This is important to prevent damage to wires and cables.

**Tips:**

* Don’t try to remove the knockout with a single, forceful blow. This can damage the electrical box.
* Work slowly and methodically around the knockout.
* Use a sharp, sturdy screwdriver.
* If the knockout is particularly difficult to remove, try using a lubricant like WD-40 to help loosen it.

### 2. Using a Punch and Hammer (for Metal Boxes)

This method uses a specialized punch tool to cleanly remove knockouts. It provides a more professional and cleaner result than the screwdriver and hammer method.

**Steps:**

1. **Position the Punch:** Place the tip of the punch on the center of the knockout.
2. **Strike with Hammer:** Strike the end of the punch firmly with a hammer. The punch should cut through the metal of the knockout.
3. **Inspect the Result:** After the first strike, inspect the knockout to see if it has been cleanly cut. If not, reposition the punch and strike again.
4. **Remove the Knockout:** Once the knockout is cut, it should fall out easily. If it’s still attached, use pliers to gently twist and remove it.
5. **Deburr the Edge:** Use a metal file or deburring tool to smooth any sharp edges around the opening.

**Tips:**

* Use a punch that is the correct size for the knockout.
* Hold the punch firmly and strike it squarely with the hammer.
* If the knockout is particularly thick, you may need to strike the punch several times.

### 3. Using Pliers (for Metal and Plastic Boxes)

Pliers can be used to twist and break off knockouts, especially in plastic boxes or thin metal boxes. Channel-lock pliers provide a wider grip and more leverage.

**Steps:**

1. **Grip the Knockout:** Use pliers to grip the edge of the knockout firmly.
2. **Twist and Bend:** Twist and bend the knockout back and forth until it weakens and breaks off.
3. **Repeat as Needed:** If the knockout doesn’t come off completely, reposition the pliers and repeat the twisting and bending process.
4. **Remove Remaining Pieces:** Use pliers to remove any remaining pieces of the knockout.
5. **Deburr (if necessary):** For metal boxes, deburr any sharp edges.

**Tips:**

* Use pliers with a good grip.
* Be careful not to damage the electrical box while twisting and bending the knockout.
* This method can be more difficult for larger or thicker knockouts.

### 4. Using a Utility Knife and Screwdriver (for Plastic Boxes)

Plastic electrical boxes are typically easier to work with than metal ones. A utility knife can be used to score around the knockout, making it easier to pry out.

**Steps:**

1. **Score the Knockout:** Use a utility knife to carefully score around the edge of the knockout on the inside of the box. This weakens the plastic and makes it easier to remove.
2. **Position the Screwdriver:** Insert the tip of a flathead screwdriver into the scored line.
3. **Pry Out the Knockout:** Gently pry the knockout outward. You may need to work your way around the knockout, prying at different points.
4. **Remove the Knockout:** Once the knockout is sufficiently loosened, it should pop out completely.

**Tips:**

* Be careful not to cut yourself with the utility knife.
* Use a sharp utility knife for a clean score.
* Apply even pressure when prying to avoid cracking the plastic box.

### 5. Using a Knockout Punch Set (for Metal Boxes – Recommended for Larger Sizes)

A knockout punch set provides the cleanest and most efficient way to remove knockouts, especially for larger sizes used for conduit. These sets use a bolt and die system to punch out a clean, round hole.

**Steps:**

1. **Select the Correct Size:** Choose the punch and die set that matches the size of the knockout you want to remove.
2. **Insert the Bolt:** Disassemble the punch and die. Insert the bolt through the center hole of the knockout.
3. **Assemble the Punch and Die:** Place the die on one side of the electrical box and the punch on the other side, with the bolt running through both.
4. **Tighten the Bolt:** Use a wrench to tighten the bolt. As you tighten, the punch will be drawn through the knockout, cleanly cutting it out.
5. **Remove the Punch and Die:** Once the knockout is punched out, loosen the bolt and remove the punch and die from the electrical box.
6. **Deburr (if necessary):** Inspect the hole and deburr any sharp edges if needed.

**Tips:**

* Use a knockout punch set that is designed for the type of metal you are working with (steel or aluminum).
* Make sure the punch and die are properly aligned before tightening the bolt.
* Apply even pressure when tightening the bolt to ensure a clean cut.

## What to Do If a Knockout is Missing and Needed

Sometimes, you might need to add a knockout back into an electrical box if one has been previously removed and is no longer needed. Here are a few options:

1. **Knockout Seals/Plugs:** These are specifically designed to fill existing knockout holes. They typically come in plastic or metal and are secured by snapping them into place or with a screw. Ensure the seal is the correct size for the knockout hole. These are readily available at most hardware stores.

2. **Electrical Tape (Temporary Fix):** While not ideal for a permanent solution, electrical tape can provide a temporary seal against dust and moisture. Cover the opening with several layers of electrical tape, overlapping each layer. This is more suitable for indoor applications.

3. **Replacement Box:** If the box has multiple unused knockouts and you are concerned about the integrity of using a plug, it might be more practical to simply replace the entire electrical box.

## Important Considerations

* **Code Compliance:** Always ensure that your electrical work complies with local electrical codes and regulations. Improperly installed wiring can be a fire hazard and can violate building codes.
* **Wire Protection:** After removing the knockout and running wires, be sure to use appropriate cable clamps or connectors to secure the wires to the electrical box. This prevents the wires from being pulled out or damaged.
* **Grounding:** Maintain proper grounding throughout the electrical system. Ensure that the electrical box is properly grounded according to code requirements.
* **Weatherproof Boxes:** If you are working outdoors, use weatherproof electrical boxes and fittings to protect the electrical connections from moisture. These boxes often have gaskets and other features to prevent water intrusion.
* **Don’t Overcrowd:** Make sure the electrical box is large enough to accommodate all the wires, connections, and devices it will contain. Overcrowding can lead to overheating and electrical problems. The National Electrical Code (NEC) specifies requirements for box fill.

## Troubleshooting Common Problems

* **Knockout Won’t Budge:** If a knockout is particularly stubborn, try using a lubricant like WD-40 or penetrating oil to help loosen it. Let the lubricant soak in for a few minutes before attempting to remove the knockout again. You can also try using a different method, such as the knockout punch set.

* **Damaged Electrical Box:** If you accidentally damage the electrical box while removing a knockout, it’s important to replace the box. A damaged box can compromise the safety of the electrical system.

* **Sharp Edges:** Always deburr the edges of the knockout hole after removing the knockout. Sharp edges can damage wires and cables, leading to short circuits and other problems.

## Conclusion

Removing a knockout from an electrical box is a straightforward process with the right tools and techniques. By following these detailed instructions and safety precautions, you can safely and effectively create openings for wiring and conduit. Remember to always prioritize safety and consult a qualified electrician if you have any doubts or concerns about your ability to perform the task correctly. Always adhere to local electrical codes to ensure safe and compliant electrical installations. Remember safety comes first. If at any point you feel unsafe, consult an electrician.