Grounding Bushing Needed??!!

[brother]

It may be petty to some, but this is to settle a debate. I found some work that was done about 4 years ago where someone ran some flex to a transformer/power distribution unit and had to use reducing washers to connect to it. this was 2" flex, its 480 volts supply, 3 phase, 3 hots and 1 ground size of wire is 3/0.

I tell the guys a 'grounding bushing is required' because of the reducing washers and the size wire 3/0 NEC 2008 300.4(G) and 250.97.

But after 250.97 closely again, I'm not sure if the 'wording' is there to require the bonding/bushing. I can only see where I win on a bushing needed but not the bonding of it. 250.97 sends you to 250.92 (B) except for (B)(1).
Am I reading this right??
So any help would be appreciated. Thanks.

 

[infinity]

Reducing washer are listed for grounding. IMO it's a poor choice to use them as such but UL feels differently.

 

[Volta]

Do you think the reducing washers comply with 250.97 exception? "Where oversized, concentric, or eccentric knockouts are not encountered . . .
(4) Listed fittings"

Even if they are listed for grounding, they are typically used when oversized ko's are encountered, and may not work for 250.97.

Relatedly, what kind of fitting is being considered in 250.92(B)(3)? Surely they don't mean crimped EMT fittings, but what else will be without threads (besides a weld)? I have always figured it referred to GRC set-screw fittings, but the screw is threaded . . .

 

[brother]

Do you think the reducing washers comply with 250.97 exception? "Where oversized, concentric, or eccentric knockouts are not encountered . . .
(4) Listed fittings"

Even if they are listed for grounding, they are typically used when oversized ko's are encountered, and may not work for 250.97.

Relatedly, what kind of fitting is being considered in 250.92(B)(3)? Surely they don't mean crimped EMT fittings, but what else will be without threads (besides a weld)? I have always figured it referred to GRC set-screw fittings, but the screw is threaded . . .

Yes they were used for oversized knockouts. It did not APPEAR to be concentric knockouts though, Im just not certain. This is basically a liquid tight flex connector, and locknuts.

I just dont like it because ive seen too many times where these reducing washers were just not 'tightened' down or secure, and its just not a good grounding means. Were talking 277/480 here.

 

[Twoskinsoneman]

I just dont like it because ive seen too many times where these reducing washers were just not 'tightened' down or secure, and its just not a good grounding means. Were talking 277/480 here.

Of all you guys that have a problem with grounding through reducing bushings have any of you ever actually had a problem? Or is this the sort of thing where it is the popular thing to say.... even though the product has been tested to do exactly that.....

I have used reducing bushings and they will tighten up just fine... If you are leaving connections that are loose do not blame the bushing, blame the bushing installer.

 

[infinity]

Of all you guys that have a problem with grounding through reducing bushings have any of you ever actually had a problem? Or is this the sort of thing where it is the popular thing to say.... even though the product has been tested to do exactly that.....

I have used reducing bushings and they will tighten up just fine... If you are leaving connections that are loose do not blame the bushing, blame the bushing installer.

IMO if the panel, box or whatever is not painted then they may provide adequate bonding. But on a painted surface I don't see how they can handle a large amount of fault current.

 

[Twoskinsoneman]

IMO if the panel, box or whatever is not painted then they may provide adequate bonding. But on a painted surface I don't see how they can handle a large amount of fault current.

I imagine you have never had the opportunity or equipment to do the tests on the bushings that are required to get a listing.

I remember my first time learning that the thread contact on a small screw (engaged in only a few threads) was an adequate means for a MBJ.
I was skeptical... but after learning about UL listing and testing I've become comfortable in the realization that I don't have expertise or facility to truly form a judgment on how a product will really perform... I leave it up to the experts.

I find it a little quizzical to hear people say "No I've never tested it myself or ever had a problem with it myself but geez I just don't feel right about this......so even though some experts have thoroughly tested this thing to do a certain something and taken all the liability for it performing, well I just don't like it."