Hazardous Location Boundary

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JUSTEINEE

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Springfield
I have a situation in a C1D1 area (Headworks of a Wastewater Plant) that I need some help with.

If a conduit is routed in the concrete floor slab and turns up in a classified area and an unclassified area a conduit seal should be placed as the conduit enters/leaves the classifed location before entering/leaving the concrete floor slab. And as I understand it no additional seal is needed at the unclassified location. Correct?

Now what if a conduit is routed in the same concrete floor slab but both ends turn up the the same classified location. Should a conduit seal should be placed as the conduit enters/leaves the concrete slab?

I guess it all boils down to where the Hazardous location boundary is located. If the concrete floor slab is considered to be part of the hazarodus location then any conduit traveling through it and into new areas would make those areas classified due to the possibility of transmission of hazarous materials.

I tend to think of the concrete floor as not being part of the classified location but am having a hard time finding anything that can back me up. And if the concrete floor slab is not considered as being part of the classified location can PVC conduit be used. I see where PVC is allowed with 24" of cover and a 2" concrete envelope in a classified location (But I am assuming the floor slab is not a Classified location) but that only makes sense in areas like aircraft hangers where belowgrade is specifically noted to be C1D1. So can i use PVC conduit in the floor slab without violating code?

Thanks for any and all help. If you need any additional information let me know. NFPA 820 was used to classify the location. Code in force is 2005 NEC but would appreciate knowing what current code dictates.
 

rbalex

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This is definitely a situation where ?expert? opinions vary. While I was on the API NEC Working Group, I was one of the original authors of what is now 501.10(A)(1)(a) Exception. It took several ?fine tunings? and I?m still not entirely comfortable that it?s finished. It was heavily debated.

While it?s all we can do on these forums, I?m emphasizing that this is only my opinion.

In various references in the Tables, NFPA 820 calls the ?enclosed space? the Division 1, location. Therefore, the floor is not in the classified location and it becomes the boundary. That said, I would not permit any fitting(explosionproof reducers excepted) between the required boundary seal and the floor. Indeed I would not permit any fittings in the raceway between the required boundary seal and the last 24? of the below grade run. (I know this isn?t what the Exception says exactly, but I?m only expressing my opinion.)

In order to use nonmetallic raceways I would want the full requirements of the Exception.

Since they don?t apply, I'm not addressing otherwise specific requirements of Articles 510 to 516. You are correct ? no seal would be required in the unclassified space.

Where the stub-ups for both ends of a raceway are in the same classified location, I personally believe that boundary seals are often useless;especially if it is a rather small ?enclosed space.? However, I would also assure myself that the classification throughout the location was based on the same source(s).
 

JUSTEINEE

Member
Location
Springfield
I am curious once again about the PVC. The code you referenced (501.10.a.1.exception) is specific to C1D1 locations correct, and we both seem to agree that the classification boundary stops at the concrete floor slab so the slab is then covered under unclassified installations, so if I use conduit seals (to maintain the classified boundary) at the transition I can use pvc in the slab without having to adhere to the rules of the exception which are specific to pvc installed in an underground classified areas such as those found at aircraft hangers.
 

rbalex

Moderator
Staff member
As long as I?ve been in the business (over 40 years) there has been a debate whether below grade or slab under a classified location should also be automatically classified. Read carefully, the Sections you cite from Articles 511 to 516 do not actually say the location is classified ? simply that certain wiring methods are specified or "as if" they are classified Division 1. They specify certain wiring methods above classified locations too.

Read the Scope and General statement of Article 510. You will note that Articles 511 through 516 are for specific applications and cannot necessarily be applied ?logically? to other installations. I know it sounds dumb ? but that?s the way it is and it has been a large part of the debates I mentioned above and in my previous post. In addition, those Articles are largely extracted from other NFPA Standards. While NFPA 820 does give direction on classification, it doesn?t on installation ? so only wiring methods from Article 501.10 apply.

An Exception must always be interpreted in context of its primary rule; i.e., Section 501.10(A)(1)(a). In this case, this is an exception to where RMC or IMC must be used as a GENERAL requirement in Class I, Division 1. No matter how much you may think there are similarities to anything in Articles 511 through 516 though, it doesn?t matter; Section 501.10 applies in any general case not specifically covered by those Articles.

Unfortunately, how below grade or floor is classified becomes a judgment call. Ironically, a good case can be made for either unclassified or Division 1, but not Division 2. (Another part of the debate).

Personally, I can live with my earlier recommendations and sleep comfortably at night; as I said before - it?s my opinion.
 
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