So from my knowledge grounding bushing’s are required for concentric knockouts when you got 4/0 or larger wire or when you’re coming up in to a panel with Ridged metal conduit. But I’m looking through the code book for the article the states that and I can’t find it does anybody know what the article # is
Grounding bushings
- Thread starter Hitschamp
- Start date
- Status
There is no specific requirement for a grounding bushing. It is one method to use when addressing grounding of services (250.92) and circuits over 250v to ground (250.97).
Wire size is not a deciding factor.
Wire size is not a deciding factor.
mtnelect
HVAC & Electrical Contractor
- Location
- Southern California
- Occupation
- Contractor, C10 & C20 - Semi Retired
Section 250.97 ...
Bonding around pre-punched concentric or eccentric knockouts is not required if the enclosure containing the knockout has been tested and listed as suitable for bonding. Fittings, such as EMT connectors, cable connectors, and similar fittings with shoulders that seat firmly against the metal of a box or cabinet are permitted to be installed with only one locknut on the inside of the box.
Bonding around pre-punched concentric or eccentric knockouts is not required if the enclosure containing the knockout has been tested and listed as suitable for bonding. Fittings, such as EMT connectors, cable connectors, and similar fittings with shoulders that seat firmly against the metal of a box or cabinet are permitted to be installed with only one locknut on the inside of the box.
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- Location
- Bremerton, Washington
- Occupation
- Master Electrician
And that rule is typically for 4S metal boxes with 1/2 and 3/4 ko’s, where the ko’s are hard to punch out, not the ones on a typical enclosure that can be easily pushed out
for the feed backThat’s good to know the wire size is not a deciding factor. that’s one of the things I here on the job is if the wire size is over 4/0 you need a grounding bushing. I hear people say a lot of different Prerequisites for grounding bushing’s and I don’t think half of them are right.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
The job site is a great source of misinformation. Don't believe everything that you hear. When in doubt ask for a code reference.
kwired
Electron manager
- Location
- NE Nebraska
A grounding/bonding bushing is sort of the #1 go to item for most people when bonding around a potentially impaired connection is required, but is not the only option either. That kind of leads many to come to conclusion this particular item is what is required simply because that is only thing they are seeing used for that purpose.
Grouch1980
Senior Member
- Location
- New York, NY
So is the engineering office. you wouldn't believe how many wrong things one has to filter through.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
I believe it. You should see some of the things that our engineering team sends out to the field. On our current project they generated a matrix for sizing all of the transformer conductors with bonding jumpers all sized too small from the wrong table.
Grouch1980
Senior Member
- Location
- New York, NY
Oh I believe that too lol. It doesn't make it easy when you have to wade through the wrong information... especially when you just start in the field.
Grouch1980
Senior Member
- Location
- New York, NY
I do have a question. In which section in article 250 does it mention that bonding is only required on one end, or both ends?
kwired
Electron manager
- Location
- NE Nebraska
250.64(E)(1) requires bonding of both ends for a ferrous raceway containing a grounding electrode conductor to said conductor. Other than that NEC is is silent, one bond point bonds the entire item in question as long as it is electrically continuous.
NEC doesn't say why, but the inductive effects on the ferrous raceway is reason you need to bond both ends when the GEC is what is contained, those effects can turn the portion with the ferrous raceway into an inductor or choke and could have current limiting effects and increased heating.
Grouch1980
Senior Member
- Location
- New York, NY
Let's say I have a 277/480 volt feeder inside EMT conduit, between 2 pull boxes. and at each end the the conduit terminates in a concentric / eccentric KO. do you need a bonding jumper on each end?
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Yes. The conduit is the EGC so the continuity must be maintained by bonding jumpers at both ends.
Grouch1980
Senior Member
- Location
- New York, NY
This I follow. What I don't understand is the thought process with bonding the metallic parts ahead of the service disconnect. Why is only one end required to be bonded, and not both ends of the conduit(s) enclosing the service entrance conductors. Shouldn't both ends be bonded?
Grouch1980
Senior Member
- Location
- New York, NY
aaaand I think I found the answer on one of your posts from awhile back:
From Infinity: (July 16, 2014)
As Dave said it's not required. A service raceway only requires bonding at one end because it is not being used as part of the fault current path.
From Infinity: (July 16, 2014)
As Dave said it's not required. A service raceway only requires bonding at one end because it is not being used as part of the fault current path.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
But there are situations where a service raceway would be a fault current path and a jumper would be required on both ends.
Grouch1980
Senior Member
- Location
- New York, NY
Ah. Understood. What type of application? Normally in my area of work we have the main bonding jumper taking the ground fault back to the neutral.
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