250.92 Services (A) & (B). Clarifications.

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Jamesco

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Master Electrician
250.92 (A) Bonding of Equipment for services.

My understanding is,
The CT cabinet, EMT conduit/s compression connectors from a CT cabinet to service main disconnecting means enclosure, cabinet, main disconnect enclosure, cabinet, shall be bonded to the grounded service conductor. Correct?

Service riser RMC connects to the CT cabinet via a compression no thread connector threaded into a myers hub connected to the CT cabinet. (punched 3" KO). The conduit is therefore bonded to the CT cabinet per 250.92 (B) (2). Correct?

250.92 (B)
"Bonding jumpers meeting the requirements of this article shall be used around impaired connections, such as, reducing washers or oversized, concentric, or eccentric knockouts".
Then followed by this sentence.
"Standard locknuts or bushings shall not be the only means for bonding required by this section" ......
That's a little confusing beings it followed the previous sentence. If I am reading its context correctly the sentence is not exclusive to the sentence about the reducing washers or oversized, concentric, or eccentric knockouts. Correct?

So just to be clear for an example.
A punched 3" ko for a 3" emt compression connector still must be bonded by using an accepted means other than the locknut supplied with the connector. Therein, 250.92 (B) (4) "Other listed devices, such as bonding type lock nuts, bushings, or bushings with bonding jumpers". That would include a bonding wedge.
Correct?
.
 
Jamesco said:
..... Therein, 250.92 (B) (4) "Other listed devices, such as bonding type lock nuts, bushings, or bushings with bonding jumpers". That would include a bonding wedge.
Correct?
.
Click to expand...

Correct. I believe it also includes the Myers hub you already have. But you should check the instructions on that. Not sure it would be legit to put a bonding wedge on a myers hub. I believe that Myers hubs with attached lugs are also a thing.
 
I thought I understood 250.92 (A) and (B) until I read this article from EC&M
www.ecmweb.com

Grounding and Bonding — Part 1 of 3

New 2011 NEC revisions clear up confusion between bonding and grounding
www.ecmweb.com www.ecmweb.com

My understanding if the KO is punched for the size of an EMT connector the regular locknut that comes with the connector is not considered an effective bonding means.
250.92 (B)

If I am understanding the EC&M article correctly the regular locknut that comes with the connector is an approved bonding means.

"Fig. 1. If a panel knockout is oversized, concentric, or eccentric - or uses reducing washers - use a bonding jumper, not a standard locknut."

And therefore 250.92 (B) (4) is not required.

(4) Other listed devices. These include bonding-type locknuts, bushings, wedges, or bushings with bonding jumpers.

Help! What am I missing? I'm totally confused now.


Also If the EMT connector locknut is an approved bonding means for service equipment then does that mean the EMT connector locknut would satisfy NEC for Bonding, connecting the service main disconnect enclosure to a load electrical panel enclosure? (EMT conduit using EMT compression connectors).

If that is the case would the connection between the two enclosures satisfy bonding requirements allowing the electrical panel enclosure to be the equipment grounding conductor for a ground fault current path to return to the grounded conductor, if KOs are punched for the size of the connectors?

(FWI, the electrical service is 3ph 4w 120/208V 600 amp. Load panel enclosure is used as the equipment grounding conductor)

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