Bonding Bushing for A/C Disconnect
- Thread starter George Stolz
- Start date
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hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
So guy's let me get this straight, concentric or eccentric knockouts are ok on load centers to bond the conduit for branch circuits, but they are not ok for grounding a disconnect enclosure that for the most part have virtually the same type of concentric or eccentric knockout?
Several years ago we discussed this issue to death here, and at one of my IAEI Western Sectionals it was a big topic, that both resulted in that for other then service conductors or GEC they were acceptable bonding means, now the code has changed this? I missed this code change
Several years ago we discussed this issue to death here, and at one of my IAEI Western Sectionals it was a big topic, that both resulted in that for other then service conductors or GEC they were acceptable bonding means, now the code has changed this? I missed this code change
Mgraw
Senior Member
- Location
- Opelousas, Louisiana
- Occupation
- Electrician
Here is a good article from UL's website on the subject.
http://www.ul.com/global/documents/...nical/ul_BondingAroundConcentricKnockouts.pdf
http://www.ul.com/global/documents/...nical/ul_BondingAroundConcentricKnockouts.pdf
DARUSA
Senior Member
- Location
- New York City
What about if you have a ground fault in your conduit?
DARUSA
Senior Member
- Location
- New York City
Bonding bushings for concentric knockout only in 277/480 volts not in 120/208 or 120/240!!!
excellent reference
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
But that does not take into account 2011 change, IMO. Still not sure about the whole thing.
chris kennedy
Senior Member
- Location
- Miami Fla.
- Occupation
- 60 yr old tool twisting electrician
How I read it.
How I read it.
Probably wrong, but here goes.
250.97 tells me to use 1 or more of the methods specified in 250.92(B) except (B)(1). That would be the following;
Therefore I believe reducing washers will still be acceptable under the 2011 for enclosures other than outlet boxes over 250V according to the following;
How I read it.
Probably wrong, but here goes.
250.97 tells me to use 1 or more of the methods specified in 250.92(B) except (B)(1). That would be the following;
Therefore I don't believe I need to read or be confused by this;
Thats not 'one of the methods' I need be concerned with.
Therefore I believe reducing washers will still be acceptable under the 2011 for enclosures other than outlet boxes over 250V according to the following;
Agreed?
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Yes but remember my quote is from 2011. Perhaps the other quote will change when the new UL book comes out.
chris kennedy
Senior Member
- Location
- Miami Fla.
- Occupation
- 60 yr old tool twisting electrician
Dennis, did you see post 30?
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I did Chris but I still don't see how RW fits into 2,3,or 4. If it did I would agree.
Why would 250.97 take us to 250.92(B) if nothing applies. Show me a situation where it would apply.
I am not sure of this at all. Just trying to understand it myself. Personally I will probably never have to worry about it however I would like to know.
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
Here's things as I see it.
Let's start simple: You have a 480V circuit in 1/2" EMT routed to a 4 square box. The way things are laid out, it's simplest for you to connect the EMT to the eccentric KO. You have two options:
1. If you use the 1/2", and leave the 3/4" ring in place. To do this, you look at 250.97, but then continue into the exception and utilize that exception that says if you have a box listed for using the concentrics/eccentrics for grounding over 250V to ground, you're fine. You install the connector and you're done.
2. If you try to do 1.), and end up accidentally knocking out the 3/4" ring, then you look at 250.97. You can either ignore the exception, and proceed to 250.97, or use condition (4) of the exception which allows listed fittings. According to QCRV, a reducing washer is a listed "fitting." It falls under the heading of "fitting" and it says in it's listing it's suitable for grounding over 250V to ground.
Let's start simple: You have a 480V circuit in 1/2" EMT routed to a 4 square box. The way things are laid out, it's simplest for you to connect the EMT to the eccentric KO. You have two options:
1. If you use the 1/2", and leave the 3/4" ring in place. To do this, you look at 250.97, but then continue into the exception and utilize that exception that says if you have a box listed for using the concentrics/eccentrics for grounding over 250V to ground, you're fine. You install the connector and you're done.
2. If you try to do 1.), and end up accidentally knocking out the 3/4" ring, then you look at 250.97. You can either ignore the exception, and proceed to 250.97, or use condition (4) of the exception which allows listed fittings. According to QCRV, a reducing washer is a listed "fitting." It falls under the heading of "fitting" and it says in it's listing it's suitable for grounding over 250V to ground.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Now that makes sense. Now why this change to 250.92 if it makes no never mind.
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
No, concentrics/eccentrics on anything besides a 4-square box are not listed for grounding over 250V to ground. So load centers, cabinets, and the two different type of switches I linked to above are out.
Concentrics/eccentrics on gutters over 100 cubic inches (BGUZ) are also out, from the looks of things.
Remember, we're focused on concentrics/eccentrics on this discussion - a hole without concentrics/eccentrics surrounding it do not need the bonding bushing.Several years ago we discussed this issue to death here, and at one of my IAEI Western Sectionals it was a big topic, that both resulted in that for other then service conductors or GEC they were acceptable bonding means, now the code has changed this? I missed this code change
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
Because that post was devoted exclusively to a box that was listed for concentric use. Now, enter the cabinets, gutters, and switches that are not listed for that use. They cannot use the exception, so they go straight to 250.92 for instructions.Now that makes sense. Now why this change to 250.92 if it makes no never mind.
250.92(B)(4) would allow the reducing washer as a "fitting" for those "dirty" boxes.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
How does 250.92(B)(4) apply to reducing washers. Other listed devices such as bonding type locknuts, bushings, or bushing with bonding jumpers. Not sure I see reducers in this scenario but I see how one might.
Good point!
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
If not in this scenario, then what scenario would the special listing (over 250V) kick in?
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