Bonding Bushing for A/C Disconnect

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My first thought is Georges questions are usually a set up. My second thought was, not if you use non-metallic conduit.
 
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:confused:
 
I would think if you are pulling an egc with the ccc, then no bonding bushing is required. If the emt is used as egc, then my guess is yes.
 
Dennis Alwon said:
250.97 takes us to 250.92(B) except B(1). The highlighted section is brand new to 2011.

(B) Method of Bonding at the Service. Bonding jumpers meeting the requirements of this article shall be used around impaired connections, such as reducing washers or oversized, concentric, or eccentric knockouts. Standard locknuts or bushings shall not be the only means for the bonding required by this section but shall be permitted to be installed to make a mechanical connection of the raceway(s).
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Mgraw said:
How about 250.97 EX. 4

From UL
GROUNDING
Metal reducing washers are considered suitable for grounding for use in circuits over and under 250 V and where installed in accordance with ANSI/NFPA 70, "National Electrical Code." Reducing washers are intended for use with metal enclosures having a minimum thickness of 0.053 in. for non-service conductors only. Reducing washers may be installed in enclosures provided with concentric or eccentric knockouts, only after all of the concentric and eccentric rings have been removed. However, those enclosures containing concentric and eccentric knockouts that have been Listed for bonding purposes may be used with reducing washers without all knockouts being removed.
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These two documents do seem to be in conflict.
 
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;

(2) Connections utilizing threaded couplings or threaded
hubs on enclosures if made up wrenchtight
(3) Threadless couplings and connectors if made up tight
for metal raceways and metal-clad cables
(4) Other listed devices, such as bonding-type locknuts, bushings,
or bushings with bonding jumpers
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Therefore I don't believe I need to read or be confused by this;

(B) Method of Bonding at the Service. Bonding jumpers
meeting the requirements of this article shall be used
around impaired connections, such as reducing washers or
oversized, concentric, or eccentric knockouts. Standard
locknuts or bushings shall not be the only means for the bonding
required by this section but shall be permitted to be installed
to make a mechanical connection of the raceway(s).
Click to expand...
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;

From UL
GROUNDING
Metal reducing washers are considered suitable for grounding for use in circuits over and under 250 V and where installed in accordance with ANSI/NFPA 70, "National Electrical Code." Reducing washers are intended for use with metal enclosures having a minimum thickness of 0.053 in. for non-service conductors only. Reducing washers may be installed in enclosures provided with concentric or eccentric knockouts, only after all of the concentric and eccentric rings have been removed. However, those enclosures containing concentric and eccentric knockouts that have been Listed for bonding purposes may be used with reducing washers without all knockouts being removed.
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Agreed?
 
chris kennedy said:
Dennis, did you see post 30?
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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.
 
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.
 
hurk27 said:
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?
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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.

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:confused:
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Remember, we're focused on concentrics/eccentrics on this discussion - a hole without concentrics/eccentrics surrounding it do not need the bonding bushing.
 
Dennis Alwon said:
Now that makes sense. Now why this change to 250.92 if it makes no never mind. :)
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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.

250.92(B)(4) would allow the reducing washer as a "fitting" for those "dirty" boxes.
 
George Stolz said:
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.

250.92(B)(4) would allow the reducing washer as a "fitting" for those "dirty" boxes.
Click to expand...
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.
 
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