I’m still learning things. On a job with class 1 div 2 classification I’m being told that I can’t use metal sch 40 NPT pipe caps to cap off some unused RMC conduits, but that I have to use the listed metal close up plugs instead per 500.E3. Those are just plugs that screw into an RMC coupling. I’m confused about why the code insists on this. RMC couplings thread onto conduit with much less resistance than fittings that are made for gas piping. So screwing a RMC coupling on top of a unused conduit and then screwing a plug that is listed for class one division two locations into that likely has less sealing power than a non-electrical steel pipe cap. I could see sort of if this was at an explosion proof enclosure where maybe we actually want the burning gases in an exposure to slowly escape. However at the unused conduit, the goal is just to keep vapor from even getting it in the first place.
Caps For Unused Conduits
- Thread starter smithtex
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- Location
- Mission Viejo, CA
- Occupation
- Professional Electrical Engineer
I have a couple of questions/comments of my own first:
BTW, where did you get the idea that a plug is listed for any Classified location? Trick question: How do you know RMC is listed for a Classified location?
- I have no idea what "500.E3" you are citing is; i.e., I don't know who/what your source of this information is.
- What you are describing is potentially a boundary seal covered in Section 501.15(B)(2), where the opening sentence is, "A conduit seal shall be required in each conduit run leaving a Class I, Division 2 location." However, the closing sentence is, "Such seals shall not be required to be explosionproof but shall be identified for the purpose of minimizing the passage of gases permitted under normal operating conditions and shall be accessible."
BTW, where did you get the idea that a plug is listed for any Classified location? Trick question: How do you know RMC is listed for a Classified location?
- Location
- Mission Viejo, CA
- Occupation
- Professional Electrical Engineer
Well, I think I found "500.E3". Properly cited, it's 500.8(E)(3). In any case you are correct that its referring to explosionproof enclosures, not raceways. (Time for a PI "clarification") Of course, technically raceways might be considered enclosures too (it's a defined term in Art 100). That said, I doubt the blanking elements or close-up plugs are listed specifically for hazardous locations although they are suitable under Section 500.8(A) because they are required to be listed under Section 344.6. (Another PI may be in order)
- Location
- Mission Viejo, CA
- Occupation
- Professional Electrical Engineer
I'm surprised - I actually found a few close-up plugs specifically UL "marked" for Class I and II. This apparently is because they are identified/associated with explosionproof enclosures rather than raceways.
RMC is not typically UL marked for Class I - so how do I know I can use it in Classified locations? Because NEC Sections 344.10(A)(1) and 501.10 (A)(1)(1) says I can. That is, if it's listed as RMC as required by Section 344.6 and marked as required by Section 344.120, it's suitable for classified locations. [Section 500.8(A)]
RMC is not typically UL marked for Class I - so how do I know I can use it in Classified locations? Because NEC Sections 344.10(A)(1) and 501.10 (A)(1)(1) says I can. That is, if it's listed as RMC as required by Section 344.6 and marked as required by Section 344.120, it's suitable for classified locations. [Section 500.8(A)]
Yes I did cite my reference incorrectly on first attempt and I was meaning to say 500.8E3. 500.8 deals with equipment, not just enclosures. This would include wiring methods such as conduit. There are listed conduit plugs for hazardous locations. One was included in a link on my initial post.
You get an RMC coupling, screw it onto the unused RMC conduit, and then screw one of these listed plugs into it. The result is a connection that has a lower quality seal than if you had screwed a galvanized pipe cap that is made to NPT threads and is tapered in a manner so as to actually prevent leaks even while under pressure.
You get an RMC coupling, screw it onto the unused RMC conduit, and then screw one of these listed plugs into it. The result is a connection that has a lower quality seal than if you had screwed a galvanized pipe cap that is made to NPT threads and is tapered in a manner so as to actually prevent leaks even while under pressure.
- Location
- Mission Viejo, CA
- Occupation
- Professional Electrical Engineer
It may seem counterintuitive, but a "lower quality seal" is ok. You really aren't going to "seal" anything for the raceways in question. Depending on the actual nature of the classified location, gases/vapors are unlikely to be "minimized" [Section 501.15, IN No. 1] from a Division 2 source, because there shouldn't be that much gas/vapor to minimize in the first place. (That's what Division 2 is all about) The fact is, without a significant pressure differential across the entire conduit run, gases/vapors aren't going to move.
As I said in my original response, "In my opinion either a conduit cap or plug would be suitable."
As I said in my original response, "In my opinion either a conduit cap or plug would be suitable."
I've never seen a sch 40 npt metal pipe cap that was UL listed or had any type of listing. I believe the threading is different as well. I would agree that coupling + plug is the correct route.
- Location
- Illinois
- Occupation
- retired electrician
The NEC and the product standards require that conduits use the same threads as plumbing pipe. That is NPT with a 3/4" per foot taper on the threads.
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