Does RMC threaded into a drilled / tapped hole require a bushing?

C

cowski

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Location
New York
Occupation
Engineer
We're running threaded rigid conduit to explosion proof enclosures that are provided with drilled and tapped 3/4NPT holes (the manufacturer, Adalet, provides the enclosures drilled and tapped holes -- they are not added in the field...).

Are we required to provide an insulating bushings per 344.46? Or does a threaded RMC connection fall under the "unless the box fitting or -enclosure is designed to provide such protection" exemption? I wouldn't think so. I guess I would want to run my hand along the hole inside the enclosure to see how sharp it is...

Would you use a knockout bushing for this?
1713212180288.png
Or a chase bushing?
1713212248597.png

Or something better than I don't know about? A plastic PVC bushing even though it's an RMC hole? It's just providing some insulation...
1713212495374.png
 
LarryFine said:
None of the above. The inside of the holes should have rounded surfaces.
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Have never seen that on the type of enclosure asked about in this thread. The wall of the enclosure is drilled and then tapped...there is no smooth rounded surface. The edges are sharp on the inside. There is no good way to comply with the code requirements for this type of enclosure.

I have seen sheet rubber used for this and I have seen the conduit with extra long threads so that the threads extend into the enclosure and a plastic bushing used.
 
cowski said:
We're running threaded rigid conduit to explosion proof enclosures that are provided with drilled and tapped 3/4NPT holes (the manufacturer, Adalet, provides the enclosures drilled and tapped holes -- they are not added in the field...).

Are we required to provide an insulating bushings per 344.46? Or does a threaded RMC connection fall under the "unless the box fitting or -enclosure is designed to provide such protection" exemption? I wouldn't think so. I guess I would want to run my hand along the hole inside the enclosure to see how sharp it is...

Would you use a knockout bushing for this?

Or something better than I don't know about? A plastic PVC bushing even though it's an RMC hole? It's just providing some insulation...
Click to expand...
Another bushing that can be used if you feel the need for them, they are good for flex as well.
Thomas & Betts 423 Insuliner Insulating Sleeve
1713217164850.png
 
I've never used an insulating bushing on the inside of an explosion proof enclosure in my career.

JAP>
 
infinity said:
Don,
Do you have an example of this type of enclosure that doesn't have an integral smooth edged hub?
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Every single explosion proof enclosure that has either field drilled and tapped holes or factory drilled and tapped holes, in locations that you specify when you order the box.
1713218864962.jpeg
 
don_resqcapt19 said:
Every single explosion proof enclosure that has either field drilled and tapped holes or factory drilled and tapped holes, in locations that you specify when you order the box.
View attachment 2571176
Click to expand...
You are right these xproof enclosures do not have the same rolled protective lip that a GUA or form7 fitting has.

I’ve either made my threads just long enough to be flush or threw a plastic bushing on.
 
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