Why Is My Panel Missing Knockouts and How Do I Plug Them?

Why Is My Panel Missing Knockouts and How Do I Plug Them?

Electrical panel knockouts are pre-scored openings in the panel enclosure that can be removed to install breakers or cables. When a knockout is removed and the corresponding slot is not used, or when a breaker is later removed, the opening must be filled to maintain the panel’s integrity as an enclosure. Open knockouts create a shock hazard to anyone working inside or near the panel and violate the Ontario Electrical Code requirement that panel enclosures be closed.

Why Knockouts Must Be Filled

• Open panel slots expose live bus bars and energized conductors — fingers, tools, or rodents can contact them
• The Ontario Electrical Code requires that panel enclosures be mechanically complete — all unused openings must be closed with listed filler plates or blanks
• ESA inspectors flag open knockouts as a deficiency that must be corrected before a certificate of acceptance is issued
• Insurance claims may be denied if an electrical fire or injury is linked to an open panel that was not properly maintained

How to Fill Open Knockouts

Breaker-slot blanks (also called filler plates or dead-front covers) are inexpensive plastic or metal plates that snap or screw into unused breaker slots. They must be listed for use with the specific panel brand and model — panels from different manufacturers are not interchangeable. Conduit knockouts can be closed with listed knockout seals (rubber or metal plugs). If your panel has open slots or missing knockouts, they should be filled as soon as possible. EZSMART can inspect your panel, supply correct filler plates, and correct any other deficiencies found during the inspection. Contact us for a panel assessment across Ontario.

Amir Azimipour

Electrician Since 2008 Journeyman Electrician Designated Master Electrician at EZSMART Corp