Concentric Knockout question

Old 08-18-14, 11:07 AM
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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, 11:20 AM
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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, 01:02 PM
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Once installed the box should have no stress on it so the knockouts should not be an issue.

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