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Old 03-05-2013, 08:24 PM   #1
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Default bonding-type locknut

( at the end of the bonding scenario described below, please agree or disagree, etc, that no 'bonding jumper' is needed since the bonding-type locknut alone provides sufficient bonding ).

Re: bonding at service

bonding of metal raceway (running from meter can to service disconnect enclosure)

relying on premise that only one end of metal raceway needs bonding to grounded service conductor

no ringed knockout (i.e., for connection of metal raceway to enclosure of service disconnect, the knockout has no knockout rings )


Question is:

If bonding-type locknut is used on connection of the metal raceway to service disconnect enclosure, then that bonding-type locknut by itself, and without bonding jumper, is sufficient bonding as far as code compliant bonding of the metal raceway ? (i.e., bonding path for metal raceway would be through the bonding-type locknut, onward through the metal enclosure enclosing the service disconnect, to the bonded service neutral bus, the service neutral bus itself being bonded to the enclosure by 'main bonding jumper' ).

So, question is...
in this scenario, no 'bonding jumper' wire is needed (for use with the bonding-type locknut), right ?

--Zaped


Last edited by Zaped; 03-06-2013 at 09:07 AM.
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Old 03-05-2013, 10:30 PM   #2
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agree

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Old 03-05-2013, 11:24 PM   #3
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Originally Posted by Cletis View Post
agree
I'm waiting on a second opinion...
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Old 03-06-2013, 02:56 PM   #4
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Quote:
Originally Posted by Zaped View Post
( at the end of the bonding scenario described below, please agree or disagree, etc, that no 'bonding jumper' is needed since the bonding-type locknut alone provides sufficient bonding ).

Re: bonding at service

bonding of metal raceway (running from meter can to service disconnect enclosure)

relying on premise that only one end of metal raceway needs bonding to grounded service conductor

no ringed knockout (i.e., for connection of metal raceway to enclosure of service disconnect, the knockout has no knockout rings )


Question is:

If bonding-type locknut is used on connection of the metal raceway to service disconnect enclosure, then that bonding-type locknut by itself, and without bonding jumper, is sufficient bonding as far as code compliant bonding of the metal raceway ? (i.e., bonding path for metal raceway would be through the bonding-type locknut, onward through the metal enclosure enclosing the service disconnect, to the bonded service neutral bus, the service neutral bus itself being bonded to the enclosure by 'main bonding jumper' ).

So, question is...
in this scenario, no 'bonding jumper' wire is needed (for use with the bonding-type locknut), right ?

--Zaped
Referencing 2011 NEC Hard cover Article 250.92(B); Commentary Summary

"Standard locknuts, sealing locknuts, and metal bushings are not acceptable as the sole means for bonding a raceway or cable to an enclosure on the LINE side of the service disconnecting means regardless of the type or condition of the knockout..."<snip>

"...bonding jumpers are required to ensure that any bonding connection will provide a suitable path for the high levels of ground fault current that is generally available on the LINE side of the service disconnecting means and OCPD. For the same means, standard locknuts and metal bushings that may be a suitable bonding connection at some locations on the load side of the service equipment are NOT considered to be a reliable bonding connection at this point in the electrical system and cannot be relied upon as the 'sole' bonding connection."

The reason is that the enclosure wall thickness can only handle a certain amount of ground fault current before it melts. This ground fault current is much higher on the LINE side of the SD, and that current needs to be grounded reliable to be able to trip the LINE side OCPD. Adding a hub with a grounding locknut (i.e. has a provision for a lug), or a separate grounding bushing with a lug to the RMC, which is bonded with a jumper to the neutral bus, will meet the requirement.

Hope that helps clarify....

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Old 03-06-2013, 05:02 PM   #5
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Default bonding type locknut

Quote:
Originally Posted by LJSMITH1 View Post
Referencing 2011 NEC Hard cover Article 250.92(B); Commentary Summary

"Standard locknuts, sealing locknuts, and metal bushings are not acceptable as the sole means for bonding a raceway or cable to an enclosure on the LINE side of the service disconnecting means regardless of the type or condition of the knockout..."<snip>


Thanks Larry. I wonder if anybody would give thumbs up to a 'bonding-type locknut' in place of a 'standard locknut' ? That is, a bonding-type locknut alone--without any locknut-to-neutral bus bonding jumper. ???? --Zaped

( 250.92(B)(4) seems to make 'bonding type locknuts' ok [I am looking at 2008 NECH], but despite what (B)(4) just sez, does anybody actually also buy into what (B)(4) sez as to adequacy of 'bonding type locknut' alone, w/o bonding jumper, I am wondering. ).

Last edited by Zaped; 03-06-2013 at 05:14 PM.
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Old 03-06-2013, 05:15 PM   #6
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Quote:
Originally Posted by Zaped View Post
Thanks Larry. I wonder if anybody would give thumbs up to a 'bonding-type locknut' in place of a 'standard locknut' ? That is, a bonding-type locknut alone--without any locknut-to-neutral bus bonding jumper. ???? --Zaped
A bonding type locknut looks like this (but it has no provsion for a bonding jumper or lug):



Is not rated to attach a bonding lug to the screw. These types of locknuts are really meant for high vibration environments to prevent loosening of the locknut and do not enhance current carrying capability of the enclosure. Also, you cannot attach a lug to that pointy screw. Also See 250.8(A) which requires an approved bonding conductor connection (i.e. Lug)


The only solution is to apply a "Grounding Wedge" like this under the conduit locknut. You can then attach a grounding lug to one of those screws:



If you have a "Meyers" style hub coming in at the service entrance, there are hubs with bonding/grounding locknuts available like this:



OR a apply grounding bushing to the conduit (assuming you have threads exposed):




OR you can try Bridgeport's new SPLIT GROUNDING BUSHING if you have conductors already pulled.



Either way, you will need to figure out an approved method to bond your service raceway to the neutral bus independent of the enclosure.

IF your service disconnect has a threaded boss adapter plate on top, then no separate bonding jumper is required per 250.92(B)(2).
Hope this helps.
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Last edited by LJSMITH1; 03-06-2013 at 05:35 PM. Reason: additional info
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Old 03-06-2013, 06:29 PM   #7
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Quote:
Originally Posted by LJSMITH1 View Post
A bonding type locknut looks like this (but it has no provsion for a bonding jumper or lug):



Is not rated to attach a bonding lug to the screw. These types of locknuts are really meant for high vibration environments to prevent loosening of the locknut and do not enhance current carrying capability of the enclosure.
A bonding locknut is not for bonding?
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Old 03-06-2013, 06:43 PM   #8
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Quote:
Originally Posted by Zaped View Post
Thanks Larry. I wonder if anybody would give thumbs up to a 'bonding-type locknut' in place of a 'standard locknut' ? That is, a bonding-type locknut alone--without any locknut-to-neutral bus bonding jumper. ???? --Zaped

( 250.92(B)(4) seems to make 'bonding type locknuts' ok [I am looking at 2008 NECH], but despite what (B)(4) just sez, does anybody actually also buy into what (B)(4) sez as to adequacy of 'bonding type locknut' alone, w/o bonding jumper, I am wondering. ).
In my opinion bonding lock nuts are in fact intended for, listed for and acceptable to the NEC for bonding.

There are listed under GROUNDING AND BONDING EQUIPMENT (KDER) in the UL general directory along with bonding busings etc.

The fact they have no provision for lug or conductor does not matter.

Quote:
250.92 Services.
(B) Method of Bonding at the Service. Bonding jumpers
meeting the requirements of this article shall be used
around impaired connections, such as reducing washers or
oversized, concentric, or eccentric knockouts. Standard
locknuts or bushings shall not be the only means for the bonding
required by this section but shall be permitted to be installed
to make a mechanical connection of the raceway(s).

(4) Other listed devices, such as bonding-type locknuts, bushings,
or bushings with bonding jumpers
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Old 03-06-2013, 07:02 PM   #9
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A bonding locknut is not for bonding?
These being called a "bonding locknut" is a misnomer. ALL listed locknuts are rated for bonding per UL514B. This version with the angled screw is NOT listed for Grounding per UL467. It is merely an enhanced version of standard locknut that is impervious to vibration. The primary reason it cannot be listed for grounding is it has no provision for a wire connector. That screw cannot be used for an attachment point for a wire conductor. Period.
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Old 03-06-2013, 07:18 PM   #10
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In my opinion bonding lock nuts are in fact intended for, listed for and acceptable to the NEC for bonding.

There are listed under GROUNDING AND BONDING EQUIPMENT (KDER) in the UL general directory along with bonding busings etc.

The fact they have no provision for lug or conductor does not matter.
In the case of 250.92 it does matter if it has a provision for a lug since it is required to provide a bonding jumper. We have been to multiple IAEI meetings, and visited with AHJ's where this 2008 service entrance bonding issue has come up in detail. In all cases, their NEC interpretation of 250.92 is the same as I posted previously (from the NEC Handbook), and for the same reasons. The service enclosure wall may not be sufficient to handle the higher LINE ground OPCD fault currents and reliably maintain a bond to the neutral bus. Having a pointy screw dig into said enclosure wall does nothing to improve the current carrying capability of said enclosure wall.

If you think this is wrong, overkill, or just flat out BS, please contact the NFPA 70 working group to have your opinion heard.
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Old 03-06-2013, 07:50 PM   #11
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Originally Posted by LJSMITH1

These being called a "bonding locknut" is a misnomer. ALL listed locknuts are rated for bonding per UL514B. This version with the angled screw is NOT listed for Grounding per UL467. It is merely an enhanced version of standard locknut that is impervious to vibration. The primary reason it cannot be listed for grounding is it has no provision for a wire connector. That screw cannot be used for an attachment point for a wire conductor. Period.
I like to use brassbonding wedges personally. Waybetter than pointy screw
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Old 03-06-2013, 07:58 PM   #12
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I like to use brassbonding wedges personally.

No you don't.


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Old 03-06-2013, 08:12 PM   #13
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No you don't.

Oh yes i do...
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Old 03-06-2013, 08:15 PM   #14
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Oh yes i do...
Just because you posses them does not mean you actually install them.
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Old 03-06-2013, 08:20 PM   #15
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Originally Posted by LJSMITH1 View Post
In the case of 250.92 it does matter if it has a provision for a lug since it is required to provide a bonding jumper.
Here are what the words in the NEC say, which is the code. The words in the handbook are not code.

Quote:
(4) Other listed devices, such as bonding-type locknuts, bushings,
or bushings with bonding jumpers
Now if you can explain away that 'or' you might have a point.

Quote:
Originally Posted by LJSMITH1 View Post
If you think this is wrong, overkill, or just flat out BS, please contact the NFPA 70 working group to have your opinion heard.
No need to contact anyone, the code clearly tells us you are mistaken.
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Old 03-06-2013, 08:24 PM   #16
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Just because you posses them does not mean you actually install them.
I bought 100 for $1 from an 80 yr old retired electrician and my inspector lets me use them
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Old 03-07-2013, 10:01 AM   #17
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Here are what the words in the NEC say, which is the code. The words in the handbook are not code.



Now if you can explain away that 'or' you might have a point.



No need to contact anyone, the code clearly tells us you are mistaken.

I know that the NEC handbook comments are not code, but they are a valid interpretation of code no matter if you agree with it or not. In addition, many AHJ's we have spoken with around the country also agree with this interpretation. They would prefer to see an actual bonding jumper going from the metallic service raceway/enclosure connection to the neutral bus to increase ground fault current carrying capability.

If you can get away with just a bonding locknut and an insulated bushing in your jurisdiction, more power to you.
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Old 03-07-2013, 11:47 AM   #18
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A Poco guy told me once that they prefer the primary to slowly burn for minutes upon end waiting upon the little pointy screw to open the fuse
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Old 03-07-2013, 12:23 PM   #19
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...But they are a valid interpretation of code no matter if you agree with it or not....
They may be a valid interpretation, but it's an interpretation that carries no more weight than mine or yours. The Handbook is not enforceable.
Quote:
...They would prefer to see an actual bonding jumper....
It's not up to them to enforce what they prefer. It's up to them to apply the code as written or amended.

I agree with your point that the tiny little set-screw probably doesn't have a ton of current carrying capacity, but if they are actually listed as bonding equipment separate from standard locknuts, I have a hard time seeing how we can argue that they should be disallowed.
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Old 03-07-2013, 12:48 PM   #20
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They may be a valid interpretation, but it's an interpretation that carries no more weight than mine or yours. The Handbook is not enforceable. It's not up to them to enforce what they prefer. It's up to them to apply the code as written or amended.

I agree with your point that the tiny little set-screw probably doesn't have a ton of current carrying capacity, but if they are actually listed as bonding equipment separate from standard locknuts, I have a hard time seeing how we can argue that they should be disallowed.
I am not trying to make a big deal out of this. I am just relaying my personal experience with this issue. Maybe the NEC should clarify what they mean by "Bonding Locknut". Do they mean a locknut that has a provision for a conductor lug? I don't know.

We all know there are plenty of 'grey' areas in the NEC which are open to interpretation all the time. AHJ's all over the country are interpreting the NEC despite what it says in black and white.

I can tell you from our own ground fault lab tests on these little 'bonding' locknuts, they have no more current carrying capability than a standard locknut torqued properly on a standard enclosure wall thickness. Also, the folks that have been around here for 30+ years, all say that the 'bonding' locknut got its misnomer name because it maintains a secure and reliable bond to the enclosure in high vibration or high temperature variation environments, which may loosen a standard locknut. That's it.

Personally, I think they should be called "setscrew locknuts" or something to that effect. The term "Bonding Locknut" implies that a standard conduit locknut does not electrically bond, when in fact it does.

That's all I have to say on this subject.

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