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Photos depicting concentric knockout removal.  Click for The Home Page
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Photos Depicting the Removal of Concentric Knockouts


Dear Mr. Electrician: I am installing a sub-panel next to the main electric service panel in my basement.  What is the best way to remove the pre-punched concentric knockouts to the correct size that I need without loosening the remaining outer rings? 
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Photos below are a demonstration of concentric knockout removal.
 
 
Answer: The photo on the right depicts the start of a concentric knockout removal with a view from the outside.  Begin the removal by banging it in the direction it was pre-punched from the factory.   Depending on the manufacturer, some concentric knockouts are easier to remove than others.

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Pushing the knockout in the direction that it was punched at the factory
 

The start of concentric knockout removal with a view from the inside.

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Inside view of concentric knockout pushed in. Click for next photo
Cconcentric knockout ring being rocked forth and back using Channellock Pliers

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Channellock pliers being used to twist a concentric knockout. Click for next photo
A concentric knockout ring being cut with BX Cutters

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Cutting a concentric knockout ring with BX cutters. Click for next photo
 
Another photo showing a concentric knockout ring being cut with BX Cutters

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Cutting a concentric knockout ring with BX cutters. Click for next photo
A concentric knockout ring that has been cut.  This makes it easier to remove without disturbing the remaining ring.

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Close shot of the cut concentric knockout rings.  Click for next photo
These are the two holes in the bottom of a sub-panel with the knockouts removed.
The remaining burrs can be filed off using a half round file.

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The knockouts are removed, but some burrs remain.  Click for next photo
My BX Cutters at rest. 

If you punch out too big of a hole, you can use reducing washers.  If you punch out the wrong hole, you can fill it with a knockout seal

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Click for more details on removing a concentric knockout.

Close shot of my BX cutters with the knockout openings in the background.
 

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Updated April 16, 2018

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