# Grounding bushings



## lighterup (Jun 14, 2013)

when there are concentric knock outs remaining in the hole
you are using to land EMT , Rigid steel & Flexible steel conduit


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## TGGT (Oct 28, 2012)

*250.97*

Here's one.



> Raceway and cable connections made through pre-punched concentric and eccentric knockouts are considered to be impaired connections that may not effectively carry fault current in the event of a ground fault.
> For circuits greater than 250 volts to ground, when connecting metal raceways to enclosures through concentric or eccentric knockouts that are not listed to provide a reliable bonding connection, the NEC requires the use of bonding-type locknuts, bonding bushings, and bonding jumpers to ensure raceways are effectively bonded to enclosures.
> Raceways and cable armor for circuits exceeding 250 volts to ground that are connected to enclosures through knockouts that are not oversized, concentric, or eccentric, are permitted to be bonded to the enclosure by any of the following means:





> Threadless connectors and couplings for cables having a metallic sheath.
> Double locknut connections (one locknut inside and one outside of enclosures) for RMC & IMC conduit.
> EMT, FMC, and Cable connectors that seat firmly against the box or cabinet, with one locknut on the inside of boxes, enclosures, and cabinets.
> Other listed fittings such as Myers© threaded hubs.


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## lighterup (Jun 14, 2013)

TGGT said:


> Here's one.




What he said^:thumbsup:


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## glen1971 (Oct 10, 2012)

Non-metallic enclosures in a hazardous location and teck cable..


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## matt1124 (Aug 23, 2011)

Back to back setup with meter can outside, panel inside, with a metallic nipple running through the wall with lock rings on both sides holding it.


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## telsa (May 22, 2015)

Most typical:

In the run from a SDS ( ie transformer ) to it's first OCPD... when it's in a metallic raceway.

Along the path of the GEC... when it's in a metallic raceway.

The typical 4sq// 4-11 j-box is listed for 277VAC L-N -- even with concentric knock-outs, btw.


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## TGGT (Oct 28, 2012)

telsa said:


> Most typical:
> 
> In the run from a SDS ( ie transformer ) to it's first OCPD... when it's in a metallic raceway.
> 
> ...


I don't think bonding bushings are required at a transformer in most cases. What is an SDS?

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## telsa (May 22, 2015)

SDS = Separately Derived System -- it's in the NEC.

Typically dry-type transformers, but could include auxiliary generators, etc.


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## mikedl361 (Dec 24, 2016)

Just to be clear when you say concentric ko, your talking about the manufactured ko' s that come on the panel right? But when you say eccentric does that mean making your ko with a hole saw.


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## RePhase277 (Feb 5, 2008)

mikedl361 said:


> Just to be clear when you say concentric ko, your talking about the manufactured ko' s that come on the panel right? But when you say eccentric does that mean making your ko with a hole saw.


No. Concentric means punched holes that share the same center point. Eccentric means punched holes that share an edge. Like this:


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## mikedl361 (Dec 24, 2016)

So on eccentric ko's would you use a grounding locknut or is that the same as a grounding bushing


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## RePhase277 (Feb 5, 2008)

mikedl361 said:


> So on eccentric ko's would you use a grounding locknut or is that the same as a grounding bushing


Not the same, but same use. Bushings are generally more available

Read the code article posted above carefully. It says a bonding means shall be used on eccentric and concentric KOs UNLESS they are listed to provide a reliable grounding/bonding connection. So that info will be buried deep inside manufacturer's specs somewhere.


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## HackWork (Oct 2, 2009)

lighterup said:


> when there are concentric knock outs remaining in the hole
> you are using to land EMT , Rigid steel & Flexible steel conduit


I know you are going to get mad at me like you always do when I disagree about code with you, but you don't need to use a bonding bushing in the situations you mentioned unless it's over 250V to ground or for a service entrance raceway.


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## lighterup (Jun 14, 2013)

HackWork said:


> I know you are going to get mad at me like you always do when I disagree about code with you, but you don't need to use a bonding bushing in the situations you mentioned unless it's over 250V to ground or for a service entrance raceway.


That does not make me mad and for the record I only got mad at
you one time when you piled on me about a GC who wouldn't sign my
change order. (April 2017)

I'm posting what the inspectors here would make me do , 
not that it's code. (I don't think I cited code on this one.)
Okay? Okay. I forgive you.


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## TGGT (Oct 28, 2012)

telsa said:


> SDS = Separately Derived System -- it's in the NEC.
> 
> Typically dry-type transformers, but could include auxiliary generators, etc.


I don't have any of my reference books with me, somebody borrowed my truck, but please list the article you're referring to that states that bonding bushings are required at a transformer. Looks like this is an on going debate.

http://forums.mikeholt.com/showthread.php?t=164477&highlight=bonding+bushing

http://www.electriciantalk.com/f30/bonding-bushings-transformer-72900/index2/


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## RePhase277 (Feb 5, 2008)

HackWork said:


> I know you are going to get mad at me like you always do when I disagree about code with you, but you don't need to use a bonding bushing in the situations you mentioned unless it's over 250V to ground or for a service entrance raceway.


And only if it's over 250 volts to ground and the KOs aren't listed for bonding.... But I always use them anyway because I don't need that kind of headache.


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## telsa (May 22, 2015)

It's lengthy:

250.30(A) and 250.30(A)(1) thru (8)

The installation (routing) is per 250.64(A)(B)(C)&*(E)*

The last reference is the killer.

.... Bonding shall apply at each end and to all intervening ferrous raceways, boxes, and enclosures between the service equipment and the grounding electrode....

In this instance, the dry-type transformer is deemed a SDS -- which equals Service Equipment due to the laws of physics and transformers.

So, the debate is *closed.*


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## mikedl361 (Dec 24, 2016)

So basically its only needed for 250V and above or is that wrong


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## RePhase277 (Feb 5, 2008)

mikedl361 said:


> So basically its only needed for 250V and above or is that wrong


250 V and above IF the KOs aren't rated for bonding. Or if there's service conductors passing through a metal nipple.


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## telsa (May 22, 2015)

mikedl361 said:


> So basically its only needed for 250V and above or is that wrong


No, it's wrong.

Bonding is mandated for the GEC System.

Bonding is mandated for SDS systems.

These usually run at much less than 250VAC.


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## TGGT (Oct 28, 2012)

telsa said:


> It's lengthy:
> 
> 250.30(A) and 250.30(A)(1) thru (8)
> 
> ...


I'll donate to your funeral costs just like I did for ol'Harry.

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## telsa (May 22, 2015)

TGGT said:


> I'll donate to your funeral costs just like I did for ol'Harry.
> 
> Sent from my SM-G930T using Tapatalk


How have you survived so long with your reading comprehension difficulties ?

&&&

For the rest of the readers:

Ferrous raceways become 'CHOKES' during fault current surges.

This is easily shown in national testing laboratories -- with the right equipment. ( 'Scopes )

The result of choking current is that a voltage differential is created.

It's absolutely astounding to see how high this voltage gets under fault conditions... even though it only lasts for a fraction of a second -- kind of like a lightning bolt -- which also does a LOT of damage in the blink of an eye.

&&&

EVERY inspector I've ever known is ALL OVER THIS POINT -- they don't miss it.


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## TGGT (Oct 28, 2012)

telsa said:


> How have you survived so long with your reading comprehension difficulties ?
> 
> &&&
> 
> ...


I gave you a compliment.

I take it back, no donation for you!

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