# Where is Ground Bushing Required?



## icefalkon

Potential11 said:


> From what I understand they are required on separate derived systems, a service, and where there are concentric and eccentric ko's. Any help?


Hi there,

Well yes you're correct. You need them at a service and at a SDS if you use the provided KO's. However, if you make your own holes...you can use a bonding locknut instead of a MIGB (Malleable Iron Grounding Bushing). Other instances where you might find it necessary to use a MIGB include but are not limited to lightning protection applications and some UPS system installations.


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## Potential11

icefalkon said:


> Hi there,
> 
> Well yes you're correct. You need them at a service and at a SDS if you use the provided KO's. However, if you make your own holes...you can use a bonding locknut instead of a MIGB (Malleable Iron Grounding Bushing). Other instances where you might find it necessary to use a MIGB include but are not limited to lightning protection applications and some UPS system installations.


Will a main bonding jumper be sufficient in a PV system or will Ground Bushing be required where AC CB are installed?


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## Shockdoc

Over 250 volts to ground, Centerfrugal knock outs to name a couple.


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## Dennis Alwon

Potential11 said:


> From what I understand they are required on separate derived systems, a service, and where there are concentric and eccentric ko's. Any help?


Once you are past the service no bonding bushings are required unless you have a voltage over 250v to *ground* and then not always. art. 250.97


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## 480sparky

Shockdoc said:


> Over 250 volts to ground, Centerfrugal knock outs to name a couple.


Centerfrugal? The middle of being stingy? :001_huh: :laughing:


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## icefalkon

480sparky said:


> Centerfrugal? The middle of being stingy? :001_huh: :laughing:


LOL

I think he meant concentric and eccentric...which the OP mentioned.

Here's another application where it's necessary...

Ground Riser in a building...IF run in ferrous metal conduit. EMT, GAL, IMC...if it's in FRE or PVC it is not necessary. Problem with that is...many of the large engineering firms are now speccing a 500MCM ground riser...which is ridiculous. UL did a study that over sizing the wire to 500's from 3/0 does nothing. A major problem we have with high rise construction is that the engineer will spec out the 500MCM in a 2" conduit. There is no UL listed MIGB that can handle a wire that size. Besides...BENDING the 500 to get into the split lug would be a job for Superman!


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## agoodelectrician

First time posting, hope this works. Can anyone cite the code that requires a bonding locknut or bushing IF concentric, eccentric, reducing washers, etc are NOT used? In the code it clearly states that you do not have to use bonding if you knockout all the rings. Why would bonding be required if you punch a hole in a solid steel enclosure and attach a firmly seated fitting? 
Second question, why are electricians so willing to exert effort into code interpretation to make their jobs more difficult and expensive? In researching this issue I have seen a multitude of statements saying bonding bushings are required, including references to the code and UL labs as confirmation. No where does it say that you HAVE to use bonding bushings on the line side raceway connection to service equipment, only that under certain conditions you have to. Doesn't make any sense to me.


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## TOOL_5150

Dennis Alwon said:


> Once you are past the service no bonding bushings are required unless you have a voltage over 250v to *ground* and then not always. art. 250.97


So many people at my shop do not understand this.


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## KennyW

Metallic cable connectors entered into a non metallic enclosure is another one.


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## flyboy

Use nonmetallic raceways and fittings and you won't have to worry about it.:thumbsup:


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