Concentric Knockout question

Old 08-18-14, 12:07 PM
Thread Starter
Join Date: Dec 2013
Posts: 236
Upvotes: 0
Received 0 Upvotes on 0 Posts
Concentric Knockout question

I had to use the concentric knockout in 2 1900 box for a circuit I ran with 1/2 emt. Is using the 1/2" hole on these concentrics any less secure than using the ones that don't have them?

Secure from a strength perspective and from a grounding perspective.

I was going to go as far as replacing the box to avoid using them... hopefully that wasn't necessary.
Old 08-18-14, 12:20 PM
Tolyn Ironhand's Avatar
Group Moderator
Join Date: Nov 2007
Location: United States
Posts: 14,159
Received 814 Upvotes on 685 Posts
It is not necessary. You do not have to bond around the concentric KO's with what you are doing. If you were installing service equipment, that would be a different story.

From a strength perspective, I guess they would be less strong. The KO's are designed for EMT. However, if you're concerned with strength perhaps you should be looking at rigid metal conduit instead of EMT.
Old 08-18-14, 02:02 PM
pcboss's Avatar
Forum Topic Moderator
Join Date: Jul 2002
Location: Maryland
Posts: 13,935
Received 181 Upvotes on 159 Posts
Once installed the box should have no stress on it so the knockouts should not be an issue.

Thread Tools
Search this Thread
Ask a Question
Question Title:
Your question will be posted in: