# Bonding Bushings @ transformer



## chicken steve

Wj,

Are you asking for an MBJ location, or are you referring to plain bonding of flex via bushings?

~CS~


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## wjcarty10

im just referring to the flex. I know how to bond X0 , the frame, building steel, all that fancy stuff. Everyone just had different things to say on when and where to install bonding bushings. There is no concentric KO's .. So some guys are saying we dont need to use them at all... Another guy is saying that they are required on the secondary side at both ends of the greenfield. I haven't opened to code book to check it out... Just figured id throw it out there on here and see what people had to say


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## bkmichael65

Did you run an egc?


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## wjcarty10

yes..


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## bkmichael65

wjcarty10 said:


> yes..


Then you don't need to worry about any bonding bushings


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## chicken steve

Methinks you should start here wj>



> *348.60 * *Grounding and Bonding*. If used to connect equip-
> ment where flexibility is necessary to minimize the transmis-
> sion of vibration from equipment or to provide flexibility for
> equipment that requires movement after installation, an equip-
> ment grounding conductor shall be installed.
> Where flexibility is not required after instal1ation, FMC
> shall be permitted to be used as an equipment grounding
> conductor when installed in accordance with 250.118(5).
> Where required or installed, equipment grounding con-
> ductors shall be installed in accordance with 250.134(B).
> Where required or installed, equipment bonding jump-
> ers shall be installed in accordance with 250.102


~CS~


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## MXer774

I used to only install bonding bushings on factory provided KO's, seems that my specs call for them everywhere. Recently had a 5 floor rise that required them on every conduit that entered service equipment. As far as compliance, my inspectors will pass me if my punch the hole in the enclosure, not so much a green tag if using factory KO's with no bonding bushing.


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## RIVETER

bkmichael65 said:


> Did you run an egc?


EGCs are run from the panel to the branch utilization devices.


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## eddy current

What are greenfields ?


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## ponyboy

eddy current said:


> what are greenfields ?


fmc.


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## JDJ

MXer774 said:


> I used to only install bonding bushings on factory provided KO's, seems that my specs call for them everywhere. Recently had a 5 floor rise that required them on every conduit that entered service equipment. As far as compliance, my inspectors will pass me if my punch the hole in the enclosure, not so much a green tag if using factory KO's with no bonding bushing.



Does it matter to the inspector if Concentric or Ecentric?


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## ponyboy

JDJ said:


> Does it matter to the inspector if Concentric or Ecentric?


No. The word you're looking for is "impaired"


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## Bad Electrician

So did anybody answer the question.

With a properly installed transformer, GEC installed, XO bonded, what is he suppose to do with Primary and Secondary FMC with an EGC installed in the FMC. 

Bond Bushings required or not?


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## ponyboy

Bad Electrician said:


> So did anybody answer the question. With a properly installed transformer, GEC installed, XO bonded, what is he suppose to do with Primary and Secondary FMC with an EGC installed in the FMC. Bond Bushings required or not?


I'm saying no.


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## Big R

What is the point of bonding fmc?


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## btharmy

Big R said:


> What is the point of bonding fmc?


If it becomes energized the breaker will trip instead of killing the next person who grabs it.


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## TQuade

btharmy said:


> If it becomes energized the breaker will trip instead of killing the next person who grabs it.


 Fmc is allowed to be used as a gec as long as it has metal to metal contact it shouldn't become energized and if they carried a ground wire from their panel and bonded the xfmr then carried it to their secondary equipment everything is bonded nothing should have any potential differences


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## strangedaze

I'm not breaking the book out yet, but I thought you needed it on the supply side of unprotected conductor conduit of SDS's. The bonding conductor must be sized to the total ungrounded area of the phase conductors. Not the equipment ground size. At least on the secondary. Because there is no breaker on the secondary.

But completely disregard this whole post if the transformer has a built in breaker.


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## Dennis Alwon

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


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## chicken steve

TQuade said:


> Fmc is allowed to be used as a gec as long as it has metal to metal contact it shouldn't become energized and if they carried a ground wire from their panel and bonded the xfmr then carried it to their secondary equipment everything is bonded nothing should have any potential differences


Well that depends.....

What good does an _insulated_ EGC do FMC simply running through it?

~CS~


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## varmit

Bonding bushings would be required at:
The 480 volt greenfield connector at the transformer.
Both ends of the 208 greenfield- at transformer and the panel.

Reason:
(A) This is a separately derived system, so it must be bonded similar to a service.

(B) If a GEC is installed in a ferrous raceway, where the GEC does not have a very low resistance to the to the raceway, The raceway will act as a "choke coil" limiting the current on the GEC in the event of a fault. This fault current limiting effect can slow or prevent the overcurrent device from clearing the fault and preventing equipment or conductor damage.


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## ponyboy

varmit said:


> Bonding bushings would be required at: The 480 volt greenfield connector at the transformer. Both ends of the 208 greenfield- at transformer and the panel. Reason: (A) This is a separately derived system, so it must be bonded similar to a service. (B) If a GEC is installed in a ferrous raceway, where the GEC does not have a very low resistance to the to the raceway, The raceway will act as a "choke coil" limiting the current on the GEC in the event of a fault. This fault current limiting effect can slow or prevent the overcurrent device from clearing the fault and preventing equipment or conductor damage.


Correct me if I'm wrong but if you bond xo in the transformer wouldn't that turn the ground wire in your secondary conduit into an equipment ground? And if you bond your system in the first disconnect or panel you wouldn't even have a ground wire in your secondary conduit


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## varmit

ponyboy said:


> Correct me if I'm wrong but if you bond xo in the transformer wouldn't that turn the ground wire in your secondary conduit into an equipment ground? And if you bond your system in the first disconnect or panel you wouldn't even have a ground wire in your secondary conduit


That is true, but the secondary raceway would still be required to be bonded on both ends.

It always seems to me that it is easier (more room) to do all of the bonding and grounding in the transformer, but it is permissible to do this at the first disconnect or panel.


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## strangedaze

ponyboy said:


> Correct me if I'm wrong but if you bond xo in the transformer wouldn't that turn the ground wire in your secondary conduit into an equipment ground? And if you bond your system in the first disconnect or panel you wouldn't even have a ground wire in your secondary conduit


If you bond in the transformer, what size equipment ground would you run between the transformer and first disconnect? You know, because there is no protection at all.


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## Awg-Dawg

varmit said:


> That is true, but the secondary raceway would still be required to be bonded on both ends.


 
Personal opinion or can you post where I can find that in the NEC?


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## strangedaze

http://ecmweb.com/code-basics/grounding-and-bonding-part-1-3

Figure 2


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## Awg-Dawg

strangedaze said:


> http://ecmweb.com/code-basics/grounding-and-bonding-part-1-3
> 
> Figure 2


 That's is dealing with a service, not a SDS.


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## varmit

By 2014 Code, the bonding conductor to the first over current device would be sized by new table 250.102 which is similar to 250.66 and upsizes the bonding conductor shown in table 250.122.


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## varmit

Awg-Dawg said:


> Personal opinion or can you post where I can find that in the NEC?


My code book is not handy now.


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## varmit

Awg-Dawg said:


> That's is dealing with a service, not a SDS.


Very similar grounding and bonding rules.


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## Awg-Dawg

varmit said:


> By 2014 Code, the bonding conductor to the first over current device would be sized by new table 250.102 which is similar to 250.66 and upsizes the bonding conductor shown in table 250.122.


 But, those have nothing to do with bonding bushings.


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## Awg-Dawg

varmit said:


> Very similar grounding and bonding rules.


Similar, but not the same.

Check out 250.97


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## ponyboy

strangedaze said:


> If you bond in the transformer, what size equipment ground would you run between the transformer and first disconnect? You know, because there is no protection at all.


I don't know bc I never bond in the transformer but I think it'd be sized by 250.122?


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## TQuade

chicken steve said:


> Well that depends..... What good does an insulated EGC do FMC simply running through it? ~CS~


The FMC is bonded to the panel through the connector you run a egc through it to bond the transformer and to bond secondary panel. That way you don't have to use bond bushings and you don't have to worry about if the FMC becomes disconnected you won't lose grounding potential. I do not use conduit or FMC as a egc for devices or panels I use them as raceways I carry a insulated egc to all panels and devices.


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