Junction Box Knockout

Category: infrastructure

A pre-punched, circular metal or plastic tab in an electrical box that can be popped out to accept a conduit connector.

Knockouts are stepped to accommodate multiple trade sizes (e.g., 1/2-inch or 3/4-inch). Installers use a hammer and pliers to punch out the required ring size, inserting a secure locknut connector to tie the incoming EMT or Romex cable flat to the box casing.

Common Examples

• The apprentice punched out a 3/4-inch junction box knockout to clean up the route for the incoming appliance dedicated circuit lines.
• Always seal any unused open knockout holes with verified metal closure plugs to maintain fire-containment compliance bounds.