Clarification concentric and eccentric knockouts

[Jpflex]

Just to clarify, it is still not clear to me if ALL concentric or eccentric knockouts have to be removed or if some larger knockouts can remain while securing conduit and to meet specific code.

One of my grounding and bonding books brought me a lot of confusion when it said all concentric and eccentric knockouts must be removed. What would be the purpose of having multiple sized concentric or eccentric knockouts if this were true and larger knockouts could not remain and be used?

Does removing all knockouts allow listed connectors with matching size conduit to be installed without bonding bushings at the line side of service or systems over 250 volts to ground?

Assuming we remove all eccentric and concentric knockouts at the line side of service, it seems we would NOT have to install bonding bushings if we use listed fittings for the conduit such as EMT connectors with standard locknuts? 250.92 (B) (2) threadless couplings and connectors if made wrench tight for metal raceways and metal clad cables. Would an inspector likely fail a listed EMT connector and locknut to a service or system with over 250 volts to ground just because most often bonding bushings are installed whether or not it has to be there?

Clearly a rigid metal conduit with just two locknuts could not be used to meet code for this application. However, from what I’m reading, bonding bushings do not have to be installed at the line side of service or systems over 250 volts AS LONG AS “ELECTRICAL CONTINUITY AT SERVICE EQUIPMENT….ARE ENSURED BY ONE OR MORE OF TGE FOLLOWING”

(3) THREAD-LESS COUPLINGS AND CONNECTORS IF MADE WRENCH TIGHT FOR METAL RACEWAYS AND METAL CLAD CABLES

My interpretation to this is a listed threaded or thread-less EMT connector without a bonding bushing. However, you don’t seem to ever see many examples of this as an acceptable method without bonding bushings being shown.

Is my bonding and grounding book wrong or misleading? Can concentric or eccentric knockouts remain to support smaller conduit?

It makes more sense that oversized knockouts can remain and bonding bushings not be used in various cabinets and breaker panels as long as listed conductive fittings are terminated at the end of conduit such as EMT?

 

[infinity]

If it's under 250 volts to ground then any number of rings can be left in place and the KO is still permitted to be used for bonding in both boxes and other enclosures.

Over 250 volts to ground if some of the rings are left the box has to be listed for bonding which all standard boxes are. Enclosures are not so listed.

 

[Jpflex]

If it's under 250 volts to ground then any number of rings can be left in place and the KO is still permitted to be used for bonding in both boxes and other enclosures.

Over 250 volts to ground if some of the rings are left the box has to be listed for bonding which all standard boxes are. Enclosures are not so listed.

Ok and that’s what I was thinking.

Enclosures = service or sub panel?

 

[Elect117]

To clarify, I believe it is only UL514A Metallic Outlet Boxes (QCIT product code) that are suitable for bonding without the use of additional bonding equipment mentioned in 250.97. That is the note in the NEC2020 handbook right after 250.97.

I believe gutters, pull boxes, etc. still need to meet 250.97.

https://code-authorities.ul.com/wp-content/uploads/2014/04/ul_BondingAroundConcentricKnockouts.pdf

 

[texie]

Ok and that’s what I was thinking.

Enclosures = service or sub panel?

infinity's remarks are correct but you need undestand that on the line side of a service "special" bonding is required per 250.92 for all metallic items. This would apply to all service voltages. For example, a standard connector with a lock nut would not comply even in a clean punched KO.

 

[augie47]

Is that not covered by (B)(3) ??

(3) Threadless couplings and connectors if made up tight for metal raceways and metal-clad cables