knock outs in boxes grounding : use a half inch EMT in a 1/2" to 3/4" K. O. ?

[Stevenfyeager]

Several metal boxes have a knock out 1/2" up to 3/4" in the same K.O., if I use only the 1/2" KO, will it be considered a qualified grounding connection ?
I ask because one inspector made questions about grounding using concentric knockouts. (as a problem) These box knockouts are not concentric, however, but off center.
Am I explaining my question clearly enough ?

 

[don_resqcapt19]

4" square and similar types of boxes with eccentric and concentric knockouts are listed for the purpose of grounding.

 

[AC\DC]

Only time you need a grounding-bushing/lock nut in them is when it’s 277 volt systems.

 

[infinity]

Don is correct, regardless of voltage standard boxes are all listed for bonding and grounding even over 250 volts to ground.

 

[Crash117]

Here’s part of UL listing article

 

[Stevenfyeager]

Thank you !

 

[ActionDave]

Only time you need a grounding-bushing/lock nut in them is when it’s 277 volt systems.

Not needed for metal boxes even at that voltage.

 

[AC\DC]

For concentric you have to. So if you use the 1/2 and there a grove for 3/4 still left then that would not qualify at 277 would it not

 

[AC\DC]

From reading that post#5 seems it’s only listed for over 250 volt for concretric if it’s an outlet box.
Pull boxes don’t qualify

 

[infinity]

From reading that post#5 seems it’s only listed for over 250 volt for concretric if it’s an outlet box.
Pull boxes don’t qualify

I think that you're correct. The UL standard for bonding and grounding applies only to the boxes shown. Other enclosures like disconnect switches do not have concentric or eccentric KO's that are listed for bonding and grounding when over 250 volts.

 

[ActionDave]

For concentric you have to. So if you use the 1/2 and there a grove for 3/4 still left then that would not qualify at 277 would it not

That is not correct. This is what 250.97 says

.... Where oversized, concentric, or eccentric knockouts are not encountered, or where a box or enclosure with concentric or eccentric knockouts is listed to provide a reliable bonding connection, the following methods shall be permitted:

(1) Threadless couplings and connectors for cables with metal sheaths

(2) Two locknuts, on rigid metal conduit or intermediate metal conduit, one inside and one outside of boxes and cabinets

(3) Fittings with shoulders that seat firmly against the box or cabinet, such as electrical metallic tubing connectors, flexible metal conduit connectors, and cable connectors, with one locknut on the inside of boxes and cabinets

(4) Listed fittings

 

[Strathead]

I think that you're correct. The UL standard for bonding and grounding applies only to the boxes shown. Other enclosures like disconnect switches do not have concentric or eccentric KO's that are listed for bonding and grounding when over 250 volts.

Some of them do.

 

[don_resqcapt19]

Not needed for metal boxes even at that voltage.

But be careful...it only apples to smaller boxes, not the cabinets for panelboards, disconnect switches, or larger junction boxes with KOs.

Some of them do.

I have never seen a box larger than an outlet box or device box that has the concentric KOs listed for grounding.

 

[ActionDave]

But be careful...it only apples to smaller boxes, not the cabinets for panelboards, disconnect switches, or larger junction boxes with KOs....

Correct. My comments were in the context of the OP and the wording of his question made me think he was asking about a 1900 box.