A small circular impression on the side, top, or bottom of your breaker box may not look like much. But if you have ever wondered, what is a knockout in an electrical panel, it is part of a critical safety system. Knockouts create planned entry points for electrical cables or conduit while helping the panel enclosure remain protected from damage, dust, and accidental contact.

For homeowners, the key point is simple: an unused knockout should not be left as an open hole, and removing one is not a casual DIY task. Work inside or around an electrical panel can expose you to energized parts, even when a main breaker is switched off.

What Is a Knockout in an Electrical Panel?

A knockout is a pre-stamped, removable section of metal in an electrical panel enclosure. It is typically round, although its size and design can vary. Electricians remove the correct knockout when they need to bring a cable, conduit, or approved fitting into the panel.

Think of it as a controlled opening that is built into the panel at the factory. Rather than drilling a random hole in the enclosure, an electrician can use an opening sized for common electrical connectors and conduit fittings. This helps protect wires where they enter the metal cabinet and keeps the installation organized.

Knockouts appear on service panels, subpanels, junction boxes, meter equipment, and other electrical enclosures. In a residential panel, you may see several sizes because different circuits and wiring methods require different connectors.

Why Electrical Panel Knockouts Matter

A knockout has a modest job, but it supports several important safety and performance goals. When installed correctly, the opening and its connector help keep conductors from rubbing against a sharp metal edge. They also provide a secure path for wiring to enter the enclosure.

The panel enclosure is designed to contain electrical components and reduce the chance of accidental contact. An open knockout can compromise that protection. It may allow dust, moisture, pests, or debris into the panel, depending on where the equipment is installed. It can also leave a pathway where someone could reach or brush against wiring inside the cabinet.

A properly selected connector matters just as much as the knockout itself. Cable connectors clamp and protect nonmetallic cable, while conduit connectors secure metal or PVC raceways. The right fitting depends on the wiring method, the panel location, the size of the opening, and local code requirements.

What You May See Around a Knockout

Not every circular mark in a panel is an open knockout. Some are still intact, appearing as stamped rings in the metal. Others may already have a connector installed. A panel can also have concentric knockouts, which are rings within rings that allow an electrician to create different-sized openings from the same location.

If a knockout has been removed but is no longer needed, it should generally be closed with an approved knockout seal. This is a metal plug made for the purpose. Tape, cardboard, insulation, or a makeshift cover are not appropriate repairs for an opening in a panel enclosure.

You may also notice that some panel openings are occupied by conduit while others have cables entering through connectors. This is normal when the work is neat, properly secured, and suited to the equipment. What is not normal is a loose cable passing through bare metal, an oversized hole around a connector, or an open space with no approved cover.

Knockouts Are Not Breaker Blanks

Homeowners sometimes confuse knockouts with the rectangular spaces on the front of a panel cover. Those rectangular spaces are breaker openings. If a breaker position is unused, it needs the correct filler plate or blank designed for that panel cover.

Knockouts are located in the metal cabinet itself, usually on the sides, top, or bottom. Both types of openings matter, but they serve different purposes. A missing breaker blank can expose the panel interior from the front, while an open knockout creates an opening through the enclosure.

When Is It Safe to Remove a Knockout?

An electrician may remove a knockout during a planned installation, such as adding a new circuit, installing a subpanel, replacing an outdated panel, or connecting a generator, EV charger, hot tub, or major appliance circuit. The opening must be the right size and location for the approved connector and wiring path.

It is not always as simple as choosing the nearest available circle. Some knockout locations can interfere with wire-bending space inside the panel. Others may be unsuitable for the size of conduit needed. The panel manufacturer’s instructions and the specific circuit design both matter.

There is also a practical issue: once a knockout is removed, it cannot be put back. If the opening is not used correctly, it must be sealed with an approved fitting. Removing the wrong knockout can leave an unnecessary opening and may make a panel look poorly modified during a home inspection.

Why Homeowners Should Not Remove Panel Knockouts Themselves

Removing a knockout can require working directly beside energized conductors. In many panels, the service wires feeding the main breaker may remain live even after you turn off the main breaker. Those components carry serious shock and arc-flash risk.

There is also a risk of damaging the panel enclosure, loosening nearby connections, or creating metal debris inside the cabinet. A loose metal slug or shavings near energized equipment can cause problems that are not immediately obvious.

For these reasons, adding a circuit is more than punching out a metal circle and feeding in a cable. It requires load calculations, correct breaker selection, wire sizing, grounding and bonding checks, secure terminations, and inspection of the panel’s overall condition. A panel that is already full, undersized, damaged, or outdated may need a different solution than simply adding another opening.

Signs a Panel Knockout Needs Professional Attention

Take a close look at the outside of your panel without removing the cover. If you see an open hole, a loose connector, a cable entering through unprotected metal, rust around an opening, or a makeshift patch, schedule an electrical evaluation. These issues may be minor to correct, but they should not be ignored.

You should also call an electrician if you are planning equipment that needs a dedicated circuit. Level 2 EV chargers, electric ranges, heat pumps, dryers, hot tubs, generators, and workshop equipment can place significant demands on a home’s electrical system. The panel may have physical space for a breaker without having enough electrical capacity for the added load.

A professional can determine whether your existing panel can safely support the project, whether a subpanel makes sense, and which knockout and connector arrangement will keep the installation clean and code-conscious.

What Happens During a Professional Repair or Installation?

An electrician begins by assessing the panel type, available capacity, circuit routing, grounding, and condition of the existing equipment. For a simple open knockout, the repair may involve installing an approved seal after confirming that no wiring changes are needed.

For a new circuit, the electrician selects the appropriate entry point, uses a listed connector or conduit fitting, protects the cable or conductors, and makes the required terminations. They also verify that the panel cover fits correctly when the work is complete. Good panel work should look orderly, secure, and intentional, not crowded or improvised.

If an inspection reveals overheating, corrosion, damaged bus bars, double-tapped conductors, outdated equipment, or insufficient capacity, the conversation may shift toward repair or an electrical panel upgrade. That is not always the answer, but it is better to address a larger problem early than build a new circuit onto unsafe equipment.

An electrical panel is the control center for your home, and every opening in its enclosure deserves the same care as the breakers inside it. If you notice an open or questionable knockout, or you are planning an upgrade that requires new wiring, Stella Electric can help you get a clear answer and a safe, complete solution.