EZSMART Corporation, ESA/ECRA #7012690 , North York , Ontario
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Peek at your electrical panel enclosure and you might notice one or two small round or rectangular holes where the metal has been punched out but nothing was ever installed. Those are missing knockouts, and Ontario code does not allow them to stay open. This guide covers what knockouts are, why they end up missing, why it matters, and how to plug them safely in a Toronto or GTA home.
A knockout is a pre-scored disc in the sheet-metal wall of the panel enclosure that can be removed to admit a cable or conduit. When a knockout has been removed but nothing was installed in the hole, or when a conduit or cable that once passed through has been removed, the enclosure is now open to insects, rodents, moisture, and airflow that carries dust into live components. Under the Ontario Electrical Safety Code, an open unused knockout must be sealed with a listed knockout closure plug of the correct size.
The proper solution is a listed knockout closure plug matched to the specific knockout size (typically 1/2 inch, 3/4 inch, 1 inch, or 1-1/4 inch trade size in residential panels). These are inexpensive stamped-steel or die-cast plugs that snap or screw into the empty hole. Some are one-piece with a nut on the back; others are two-piece with a snap ring. Both types are cheap and available at any electrical supply house.
Not acceptable substitutes:
All of the above will be flagged on inspection and will not restore proper arc containment.
Plugging an unused knockout on the OUTSIDE surface of the panel enclosure, without removing the deadfront and without touching any live components, is a task some homeowners can perform safely. The knockout plug goes in from the outside, the retaining nut or snap ring engages from behind, and you never have to expose the live bus. It is one of the least risky panel-adjacent tasks.
However, in Ontario, panel work of any kind is a grey area for DIY. If the empty knockout is next to a cable that is not properly bushed, if there is any doubt about the plug size, or if the panel has other issues, book an ESA-licensed electrician. Related: can a homeowner change their own electrical panel legally.
If the panel is outdoors or in a garage subject to weather, the plug must also be rated for the enclosure’s NEMA rating. NEMA 3R and NEMA 4 enclosures need listed watertight or weatherproof plugs to maintain their rating. See can water get inside an outdoor breaker box. Do not use indoor knockout plugs on an exterior panel.
It is one of the cheapest OESC defects to fix. There is no reason to leave an open knockout in place.
Every time we open a panel for any reason in a GTA home, the first walkaround check is the enclosure skin. Open knockouts, cable jackets nicked by unbushed entries, and rust rings around old conduit connections are the three most common overlooked defects, and every one of them started as a lazy shortcut on an install years earlier. If you have never had a licensed contractor do a five-minute walkaround of your panel enclosure, add it to the next service call. Cheap fix, real safety improvement, and a clean ESA record if anyone ever asks.
Yes. Every unused knockout must be sealed with a listed closure plug under the OESC.
No. Duct tape, foil tape, and electrical tape are not code-approved substitutes for a listed knockout plug.
It can be, when done from the outside without opening the deadfront. If in doubt, book a licensed contractor.
Under $2 CAD each at any electrical supply house. Install time is under a minute per plug.
Yes. Weatherproof plugs rated for the panel’s NEMA enclosure rating are required outside.
Panel with open knockouts, missing filler plates, or ratty cable entries in a Toronto or GTA home? Call ezsmart at 416-838-9006 or use our contact page. An ESA-licensed electrician will inspect and seal the enclosure to current OESC.
Electrician Since 2008 Journeyman Electrician Designated Master Electrician at EZSMART Corp
