Molly Ayala
A knock out or KO is a partially stamped opening in electrical enclosures that allows quick entry for wires, cables, or pipes. Removing a knock out from an electrical box can be done using a screwdriver and pliers. To seal an open knockout, you can use a knockout plug, knockout seal, or knockout closer. Knockout plugs are pressed or hammered into place from outside the box, while knockout seals are three-piece seals with a threaded strap, a circular cap, and a screw. Knockout closers are usually installed from the outside and can be made of plastic or metal.
Characteristics and Values Table for Sealing an Electrical Knockout:
| Characteristics | Values |
|---|---|
| Knockout Closer Installation | Installed from the outside |
| Use of Electrical Tape | Not recommended |
| Recommended Material | Plastic KO seals, UL approved |
| Snap-in Seals | Can be inserted from either side, reducing the risk of damaging wires |
| Standard Knockout Plugs | Have crimped prongs on the back that are pressed or hammered into place |
| Three-Piece Seals | Have a threaded strap, a circular cap, and a screw to connect the parts |
| Plug Sizing | Match the plug material to the box material (e.g. galvanized steel box with steel and zinc parts) |
| Knockout or "KO" | Partially stamped opening for quick wire, cable, or pipe entry |
| Removal Technique | Use a screwdriver to detach the knockout and smooth any rough edges with a deburring tool |
| Alternative Methods | Pop-in friction fit, mechanical fastener with a screw or wing nut, washers with bolts, duct tape, or box covers |
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What You'll Learn
Using plastic knock-out seals
Plastic knock-out (KO) seals are a convenient way to seal electrical knockouts. They are UL-approved and easy to install. They can be purchased in bulk and are available in various sizes.
When using plastic KO seals, it is important to match the seal size to the knockout hole size. Standard knockout plugs have crimped prongs on the back, and you press or hammer them into place from outside the box. The prongs compress and press inward to fit through the hole, then spring back to keep the plug snug and virtually impossible to remove.
However, it is worth noting that some users have expressed difficulty in installing certain types of plastic KO seals. For example, the \"claws\" inside the seal may need to be bent inward to get the seal in place, which can be challenging. Additionally, finding the right size plug for the knockout hole can be tough.
An alternative to plastic KO seals is a three-piece seal, which consists of a threaded strap on the back and a circular cap on the front, connected by a screw in the centre. To install this type of seal, you loosen the screw without removing it, then wiggle the strap through the opening and press down to get the strap through the hole.
Another option is to use a putty pad to cover the knockout opening. However, opinions vary on whether this is a legal and effective method, as putty is not a listed item for a proper knockout seal.
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Installing from the outside
Knockout closers are typically installed from the outside. Before you begin, it is important to ensure that the power is cut off at the circuit breaker to avoid any risk of shock or burns.
Standard knockout plugs have crimped prongs on the back. To install, simply press or hammer the plug into place from outside the box. The prongs will compress and press inward to fit through the hole, then spring back into place to keep the plug snug and secure.
If you are working overhead, you may need to remove the screw and reverse the direction. Press the strap through from the inside of the box, then tighten the screw from the outside.
Snap-in seals can be inserted from either side of the box, and the "claws" do not present any significant danger to the insulation on the wires. However, if you are concerned about the claws nipping wires, you can try to bend them inward before installing the seal.
If you are unable to find snap-in seals, you can use plastic knock-out seals, which are UL-approved and easier to install.
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Using snap-in seals
Snap-in seals are a type of knockout plug used to seal electrical boxes. They are designed to be inserted from either side of the box, and their "'claws' do not pose a significant risk to the insulation on the wires. While it is not necessary to bend the claws back, some people find it helpful to bend them inward to get the seal in place.
To use a snap-in seal, first, ensure that the power is cut off at the circuit breaker to avoid any risk of shock or burns. Then, locate the knock-out stamping (KO) that is sized to fit the desired connector. Pick the one that will be easiest to connect the cable or pipe. The single-size KOs and smallest of multiple KOs are generally secured in a single location.
Once you have located the correct KO, simply insert the snap-in seal into the opening. You may need to use a screwdriver to press the tabs outward to hold the plug in place. Make sure the seal is snug against the box.
Snap-in seals are available in various sizes, including 1/2 inch, 1 inch, 1-1/4 inch, 1-1/2 inch, and 2 inch. They are typically sold in boxes of 25 or 50, and can be purchased from companies like PECO Fasteners & Electrical Products and Home Depot.
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Removing rough edges
To remove the rough edges effectively, you can utilise electrical pliers. Insert the head of the pliers into the hole and twist until it has completely circumscribed the opening. This action will help dull any burrs that may be present. The metal used in the electrical box is typically soft enough for the pliers to effectively smooth out the rough areas.
Another tool that can be employed for this task is a deburring tool. This specialised instrument is designed to smooth out rough edges and create a uniform surface. By using a deburring tool, you can ensure that any remaining sharp edges are carefully removed.
In some cases, a flat-head screwdriver can also be utilised to address rough edges. By inserting the screwdriver into the slot of the knock-out and tapping or striking its handle, you can detach the knock-out. If necessary, you can then use your hands to finish removing it. This method may help in dislodging any stubborn burrs or sharp protrusions.
It is important to remember to always exercise caution when working with electrical components. Ensure that the power is cut off at the circuit breaker before initiating any work. Additionally, always wear appropriate protective gear, such as gloves, to safeguard yourself from potential hazards.
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Using a screwdriver
Sealing an electrical knock-out is important to ensure that the box can contain any fire that might start inside it. It also prevents someone from accidentally poking something through a hole and getting electrocuted, and keeps out pests, such as mice.
To seal an electrical knock-out with a screwdriver, you will first need to cut off the power at the circuit breaker box. This is important to prevent the risk of shock or burns.
Next, locate the knock-out stamping (KO) and find the point of attachment. Using a screwdriver, press the edge of the screwdriver against the inner-most KO's stamped edge, away from the point of attachment. Gently pry the screwdriver's tip into the box, ensuring that only the inner ring of the KO bends inward. Repeat this step, pressing the other portion of the KO ring into the box.
Now, press the blade against the wall, between the wall and the KO ring, to pry it further inward. You can then grab the edge with pliers and twist and rock the KO ring back and forth to break it away.
Alternatively, you can use a screwdriver to install a knockout plug. Knockout plugs have crimped prongs on the back that are pressed or hammered into place from the outside of the box. You can use a screwdriver to press the tabs outward to hold the plug in place.
Another option is to use a three-piece seal, which has a threaded strap on the back and a circular cap on the front, connected by a screw. Loosen the screw and wiggle the strap through the opening, pressing down to get the whole length of the strap through the hole.
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Frequently asked questions
A knockout closer, or knockout seal, is used to cover and seal holes in electrical boxes.
There are several types of knockout closers, including the pop-in friction fit, the mechanical fastener fit with a screw or wing nut, and the two-piece screw type. Another type is the three-piece seal, which has a threaded strap on the back and a circular cap on the front, connected by a screw.
Knockout closers can be made of metal or plastic. Metal closers are typically used for metal boxes, and plastic closers are used for plastic boxes.
Knockout closers can be purchased at hardware stores such as Home Depot, which offers Halex seals, or online at websites such as LH Dottie, which carries three-piece knockout seals.
