Bonding Bushing Question

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250.97 is the section that we are referencing.
In the main body of language in the paragraph, it gives us the requirements to follow.


There is an exception that we can reference. It states different information that we are permitted to follow.
Read the first paragraph of the exception.

Also, the reference in the main body of language for 250.92 is referencing 250.92(B), not (A).
"...Bonding jumpers meeting the other requirement of this article shall be used around concentric or eccentric knockouts that are punched or otherwise formed so as to impair the electrical connection to ground."

Most of the equipment manufactured today does not impair the connection to ground. See (BGUZ) & (QCIT) of the UL White Book

As Augie mentioned in one of his posts, additional bonding would not be required.

P.S. we are not talking about the equipment ground conductor installed in the raceway.
 
Pierre C Belarge said:
Most of the equipment manufactured today does not impair the connection to ground. See (BGUZ) & (QCIT) of the UL White Book
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I'm not convinced. Both the service disconnect and the VFD Cabinet in this example are "cabinets", and as such, fall under the UL's classification (CYIV), which does not bear the same language as contained in (QCIT), specifically stating that "outlet boxes" concentrics are suitable for grounding above 250V without additional equipment.

As Augie mentioned in one of his posts, additional bonding would not be required.
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I would wholeheartedly agree, if I could make the jump that we can ignore one end of the raceway if the other is compliantly bonded, which 250.92(B)(2) is not specific about.
 
This is how I see this application getting summed up

This is how I see this application getting summed up

250.4(A)(3)-Bonding of Electrical Equipment. Normally non–current-carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected together and to the electrical supply source in a manner that establishes an effective ground-fault current path.
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250.90 General-Bonding shall be provided where necessary to ensure electrical continuity and the capacity to conduct safely any fault current likely to be imposed.
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250.97 Bonding for Over 250 Volts.
For circuits of over 250 volts to ground, the electrical continuity of metal raceways and cables with metal sheaths that contain any conductor other than service conductors shall be ensured by one or more of the methods specified for services in 250.92(B), except for (B)(1).

Exception: 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
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Last Part of 250.92(B)
Bonding jumpers meeting the other requirements of this article shall be used around concentric or eccentric knockouts that are punched or otherwise formed so as to impair the electrical connection to ground. Standard locknuts or bushings shall not be the sole means for the bonding required by this section.
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Just wanted to post this so everyone can keep up.
 
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George Stolz said:
I'm not convinced. Both the service disconnect and the VFD Cabinet in this example are "cabinets", and as such, fall under the UL's classification (CYIV), which does not bear the same language as contained in (QCIT), specifically stating that "outlet boxes" concentrics are suitable for grounding above 250V without additional equipment.

.
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I guess this is the part I don't understand. If you had concentrics at both enclosures, I could see a "problem" , but, if I understand correctly, the VFD is a punched hole with no concrentic. Since we have an equip. ground for grounding continuity, we only need to assure the LFMC is bonded at either end.
 
augie47 said:
I guess this is the part I don't understand. If you had concentrics at both enclosures, I could see a "problem" , but, if I understand correctly, the VFD is a punched hole with no concrentic. Since we have an equip. ground for grounding continuity, we only need to assure the LFMC is bonded at either end.
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The LTFMC has to be bonded at both ends....PERIOD....
250.90 General-Bonding shall be provided where necessary to ensure electrical continuity and the capacity to conduct safely any fault current likely to be imposed
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If everything is UL listed..........standard locknuts will meet the requirement in 250.97 exception on the side without concentrics. On the side where the concentric is, 250.92(B) is required.

just a reminder....
300.12 Mechanical Continuity — Raceways and Cables.
Metal or nonmetallic raceways, cable armors, and cable sheaths shall be continuous between cabinets, boxes, fittings, or other enclosures or outlets.
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ibew441dc said:
The LTFMC has to be bonded at both ends....PERIOD....

If everything is UL listed..........standard locknuts will meet the requirement in 250.97 exception on the side without concentrics. On the side where the concentric is, 250.92(B) is required.

just a reminder....
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And where does it say that in the NEC ?

If it is being used to assure ground continuity from A to B, I would agree.
It only needs to be bonded to assure a ground return path. If cabinet
A is Bonded by whatever means, and B is bonded by the equipmemnt grounding conductor then all that is left requiring bonding is the LFMC. The connector at B, encounntering no concentric knockouts satisfyies this function without a bond bushimng.
A short within the LFMC can flow to cabinet B without encountering concentric knockouts and then through the EGC to to source.
I contend BOTH ends only need to be bonded when the conduit is the EGC.

As an exmaple, if we install a service conduit into bolted hub on a meter, we don't bond the conduit at the weatherhead.
 
ibew441dc said:
On the side where the concentric is, 250.92(B) is required.
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You are overlooking this part of 250.97 Exception: "...or where a box or enclosure with concentric or eccentric knockouts is listed to provide a reliable bonding connection..."

Pierre pointed this out in his comment, "Most of the equipment manufactured today does not impair the connection to ground. See (BGUZ) & (QCIT) of the UL White Book"

The question that remains to be answered is whether or not the disconnect with the concentric KO's is such a listed box or enclosure?
 
George Stolz said:
Indeed, I don't see an answer to this part of the question, which I posed here.
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sorry, George, I'm still lost as to why it matters.
If A is bonded (probably by the neutral) and B is bonded by the Eq Gr conductor and the nipple is bonded by it's non-concentric connection to B, the nipple at A is not relevant.
 
augie47 said:
And where does it say that in the NEC ?

If it is being used to assure ground continuity from A to B, I would agree.
It only needs to be bonded to assure a ground return path. If cabinet
A is Bonded by whatever means, and B is bonded by the equipmemnt grounding conductor then all that is left requiring bonding is the LFMC. The connector at B, encounntering no concentric knockouts satisfyies this function without a bond bushimng.
A short within the LFMC can flow to cabinet B without encountering concentric knockouts and then through the EGC to to source.
I contend BOTH ends only need to be bonded when the conduit is the EGC.
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350.6-LFMC and Associated fittings shall be listed

UL Whitebook DWTT-acknowledges LFMC fittings for Grounding under 1-1/4''
UL Whitebook DXHR-acknowleges LFMC for Grounding under 1-1/4"
( Regardless both the fittings and the conduit are metallic and the fittings require a locknut to secure them to the enclosure )

300.12- Mechanical Continuity ? Raceways and Cables.
Metal or nonmetallic raceways, cable armors, and cable sheaths shall be continuous between cabinets, boxes, fittings, or other enclosures or outlets.
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The method in which the LFMC is to be installed between two metallic enclosures as stated in Georges original post automatically require bonding to take place. But in addition to this, the last section of 250.92(B) must be complied with.Last Part of 250.92(B)
Bonding jumpers meeting the other requirements of this article shall be used around concentric or eccentric knockouts that are punched or otherwise formed so as to impair the electrical connection to ground. Standard locknuts or bushings shall not be the sole means for the bonding required by this section.
 
augie47 said:
As an exmaple, if we install a service conduit into bolted hub on a meter, we don't bond the conduit at the weatherhead.
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This is true............but this is not talking about Georges installation. My statements are specifically referring to that.
 
Smart $ said:
You are overlooking this part of 250.97 Exception: "...or where a box or enclosure with concentric or eccentric knockouts is listed to provide a reliable bonding connection..."

Pierre pointed this out in his comment, "Most of the equipment manufactured today does not impair the connection to ground. See (BGUZ) & (QCIT) of the UL White Book"

The question that remains to be answered is whether or not the disconnect with the concentric KO's is such a listed box or enclosure?
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On the contrary......it appears that you have not clearly read UL Whitebook (BGUZ) or (QCIT) or maybe you have just made the mistake of going off of someone else's reference. In fact those two sections are not even referring to the enclosures that are included in this discussion. We are talking about Cabinets and Cutout Boxes which are (CYIV). In (CYIV) there is no mention of these enclosure types meeting a requirement for above or below 250 volts.
So now back to square 1.
The short answer.........start at 250.97 and end at 250.92(B) last sentence.
 
Pierre C Belarge said:
Most of the equipment manufactured today does not impair the connection to ground. See (BGUZ) & (QCIT) of the UL White Book
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This equipment in question is not in either of those two categories. The enclosures are cabinets and/or cut out boxes which are in UL Whitebook (CYIV)
(CYIV) makes no mention or referral in respect to it being identified as G & B equipment.
 
ibew441dc said:
On the contrary......it appears that you have not clearly read UL Whitebook (BGUZ) or (QCIT) or maybe you have just made the mistake of going off of someone else's reference. In fact those two sections are not even referring to the enclosures that are included in this discussion. We are talking about Cabinets and Cutout Boxes which are (CYIV). In (CYIV) there is no mention of these enclosure types meeting a requirement for above or below 250 volts.
So now back to square 1.
The short answer.........start at 250.97 and end at 250.92(B) last sentence.
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On the contrary... it appears you didn't read my response to George's reply :rolleyes:
 
I'm to poor to pay attention....

I'm to poor to pay attention....

Smart $ said:
Ooops... missed your post :rolleyes:

In that case, the answer is: The disconnect's enclosure (or "cabinet" if you must) is not listed for concentric KO grounding.
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:grin:You mean this one:grin::grin:
 
I might be sorry for putting myself into this fire but here it goes:
I will have to side with Daniel on this one strictly based on 250.97. If anything I would say it is not required on B side if double locknuts or another approved means is used to maintain a secure connection. Side A has a concentric knockout now I don't claim to be a genius with the code but 250.97 planly says we need a bonding bushing. And where at all does it say we don't if we run a EGC I'm not seeing that anywhere. 250.96 may provide an argument but it also says with or without a supplementary EGC. I personally have a hard time with this section of the code seems like I'm always confused after reading it but the bottom line is go with the inspector and I don't see a problem with bonding both sides of the LFMC.
Ok what if..... we bond only side B what if LFMC breaks somewhere what if the connection at point A due to the concentric knockout fails or becomes loose and finally what if side towards A gets a ground fault???? I know alot of what ifs that came true.........
 
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