Concentric Knockouts

[T-Wragg]

I am running EMT from the main service panel to a sub-panel. I am entering the sub-panel through concentric knockouts. An equipment grounding conductor is also installed in the conduit for attachment to a ground bar in the sub-panel. Does the code always require a ground bushing installed when an enclosure is entered with a metal raceway through concentric knockouts? I am in California and we are using the 2008 NEC.

 

[mike7330]

no, grounding bushing only required on the service side 250.92

 

[hurk27]

And voltage over 250 volts to ground such as circuits in a 277/480 volt system.
See 250.97 which will point you to 250.92(B) excluding 250.92(B)(1)

Another place which doesn't apply to your install is where a raceway enclose a grounding electrode conductor as in 250.64(E)

And in some hazardous locations in the 500 area of the NEC.

I think that about covers it

 

[infinity]

What's the voltage, also some KO's are listed for bonding over 250 volts.

 

[don_resqcapt19]

What's the voltage, also some KO's are listed for bonding over 250 volts.

Rob,
Are there panels or disconnects with the KOs so listed? As far as I know the only things with "listed" KOs are boxes.

 

[infinity]

Rob,
Are there panels or disconnects with the KOs so listed? As far as I know the only things with "listed" KOs are boxes.

There could be be but I don't know for certain. By looking at the tangential KO's on Square D equipment I might guess that they're listed when over 250 volts but I'm unsure.

 

[templdl]

Some of those concentric knockouts can be a pain in the tush. Beyond what the NEC/or UL requires I personally would consider good judgment as to whether addition attention should be considered from a professional?s point of view.