2" conduit entering Class-1/Div.-1

[JB78]

I need to have two 2" conduits enter thru the (boundry) wall of a sewer outfall chamber (Class1, Div-1) directly from below grade. They would be entering J-boxes just inside the chamber wall, within 5'. I wanted to install the boundry seals where they emerged from grade at the exterior of the control building (50' away), which would be great if they were smaller. But since they are 2" the code requires a seal at the boxes regardless of whether the boxes would normally require one or not. I do not see any exceptions to this even though I am just stubbing-in with no fittings between the boundry and the first box. Short of reducing the specified conduit size, I'm assuming I must install the seal inside the boundry at those first boxes?

Thanks,
JB78
(first post)

 

[Smart $]

Welcome.

There doesn't appear to be any way around the seal for entering the enclosures. Can you put an "L" at the conduit penetration into the outfall chamber, then your seal before entering a box? That would get you a seal for the enclosure, then you could put a boundary seal at the control building per the underground exception. Probably not the "one stone, two bird" solution you were hoping for but it appears compliant.

 

[Dale001289]

I need to have two 2" conduits enter thru the (boundry) wall of a sewer outfall chamber (Class1, Div-1) directly from below grade. They would be entering J-boxes just inside the chamber wall, within 5'. I wanted to install the boundry seals where they emerged from grade at the exterior of the control building (50' away), which would be great if they were smaller. But since they are 2" the code requires a seal at the boxes regardless of whether the boxes would normally require one or not. I do not see any exceptions to this even though I am just stubbing-in with no fittings between the boundry and the first box. Short of reducing the specified conduit size, I'm assuming I must install the seal inside the boundry at those first boxes?

Thanks,
JB78
(first post)

Are the Junction Boxes Explosion proof, i.e. Nema 7? See 501.15(A)(1).

 

[JB78]

One J-box is NEMA-7 and the other is NEMA-4X/SS (intrinsically safe wiring). Entering at 30" below grade these runs are about 12" from the underside of the concrete deck. If the engineer will not allow using 1.5" conduit I think offsetting down a bit and installing the seal ahead of each (suspended) box would be the way to go. That would also serve as the boundry seal. Using an LB at the wall would require seals at both locations.

Thank you for the input,
JB78

 

[Dale001289]

One J-box is NEMA-7 and the other is NEMA-4X/SS (intrinsically safe wiring). Entering at 30" below grade these runs are about 12" from the underside of the concrete deck. If the engineer will not allow using 1.5" conduit I think offsetting down a bit and installing the seal ahead of each (suspended) box would be the way to go. That would also serve as the boundry seal. Using an LB at the wall would require seals at both locations.

Thank you for the input,
JB78

Keep in mind, Crouse-Hinds "LB's" are not suited for Division 1. You'll need threaded fittings rated for Class I, Division 1, such as C-H; GUA, EAB or OE series. Ref 501.10(A)(3)


http://www.cooperindustries.com/con...og-pdfs/fittings/oe-conduit-outlet-bodies.pdf

 

[JB78]

Yes. Thanks Dale. The conduit only contains #12 & #14 conductors so I could go with the Ocal GUAB. Largest available is 2".

 

[nhee2]

would the guab fitting at the entry with a GUA sealing cover work?

 

[rbalex]

Just for my curiosity at the moment, what standard is being used to classify the installation?

 

[JB78]

As per the project engineer, NFPA-820 (Standard for Fire Protection in Wastewater Treatment Plants)

JB78

 

[rbalex]

As per the project engineer, NFPA-820 (Standard for Fire Protection in Wastewater Treatment Plants)

JB78

Excellent. That's what I would use too.

I would like to correct a slight misunderstanding you may have. The 2" seal requirement applies to the conduit entry to the enclosure, not to the conduit itself. See Section 501.15(A)(1)(2):

(A) Conduit Seals, Class I, Division 1. In Class I, Division 1 locations, conduit seals shall be located in accordance with 501.15(A)(1) through (A)(4).
(1) Entering Enclosures. Each conduit entry into an explosionproof enclosure shall have a conduit seal where either of the following conditions applies:
…

(2)The entry is metric designator 53 (trade size 2) or larger and the enclosure contains terminals, splices, or taps.​

[NOTE: I underlined "entry" and offset Subsection 501.15(A)(1)(2) for emphasis. This particular Subsection designator is inconsistent with the general NEC format, it would typically be 501.15 (A)(1)(b). I used the 2014 NEC. The format has been improved in 2017, but the designator has remained the same.]

Because the raceway into the chamber is 2", a 2" seal will still will be required somewhere; however, if the enclosure entry were less than 2", then everything between the seal and the enclosure could be reduced and the seal would then only serve as a boundary seal. If this be the case, the seal would not necessarily even need to be within 18" of the enclosure since it wasn't an enclosure seal in the first place. Any wiring method otherwise suitable for Division 1 [Section 501.10(A)] would be acceptable.

Next, since below grade is unclassified there is no need to seal where the raceways emerge from grade.

If you still wished to seal only at the emergence from grade, you could still reduce all the raceways from the chamber wall into the explosionproof enclosure and remove the seals at the enclosure.

 

[Dale001289]

Excellent. That's what I would use too.

I would like to correct a slight misunderstanding you may have. The 2" seal requirement applies to the conduit entry to the enclosure, not to the conduit itself. See Section 501.15(A)(1)(2):

[NOTE: I underlined "entry" and offset Subsection 501.15(A)(1)(2) for emphasis. This particular Subsection designator is inconsistent with the general NEC format, it would typically be 501.15 (A)(1)(b). I used the 2014 NEC. The format has been improved in 2017, but the designator has remained the same.]

Because the raceway into the chamber is 2", a 2" seal will still will be required somewhere; however, if the enclosure entry were less than 2", then everything between the seal and the enclosure could be reduced and the seal would then only serve as a boundary seal. If this be the case, the seal would not necessarily even need to be within 18" of the enclosure since it wasn't an enclosure seal in the first place. Any wiring method otherwise suitable for Division 1 [Section 501.10(A)] would be acceptable.

Next, since below grade is unclassified there is no need to seal where the raceways emerge from grade.

If you still wished to seal only at the emergence from grade, you could still reduce all the raceways from the chamber wall into the explosionproof enclosure and remove the seals at the enclosure.

Bob, if the scenario were a Class I, Division 2 location, 2" conduit entering an explosion proof enclosure (w/2" or greater opening), that does NOT contain arcing devices, could the conduit seal be omitted?

thanks

 

[rbalex]

Bob, if the scenario were a Class I, Division 2 location, 2" conduit entering an explosion proof enclosure (w/2" or greater opening), that does NOT contain arcing devices, could the conduit seal be omitted?

thanks

In Division 2, a seal would not be required no matter what the conduit entry size. As you have described it, the enclosure isn't required to be explosionproof. See Section 501.10(B)(4). So - if the enclosure isn't required to be explosionproof, a seal isn't required either.

 

[Dale001289]

Thanks Bob


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[Strathead]

One J-box is NEMA-7 and the other is NEMA-4X/SS (intrinsically safe wiring). Entering at 30" below grade these runs are about 12" from the underside of the concrete deck. If the engineer will not allow using 1.5" conduit I think offsetting down a bit and installing the seal ahead of each (suspended) box would be the way to go. That would also serve as the boundry seal. Using an LB at the wall would require seals at both locations.

Thank you for the input,
JB78

Per the exception to 501.15(A) the intrinsically safe JBox doesn't require a seal.

[edit] ...at the box. A seal would still be required either above ground or at the boundary as earlier discussed.

 

[JFletcher]

Is a sewer plant outfall even a classified location? I suppose a plant with multiple outfalls or a bypass outfall *could* develop a flammable/explosive atmosphere, but that certainly wouldnt be the norm or possible even under faulty conditions...

 

[Smart $]

Is a sewer plant outfall even a classified location? I suppose a plant with multiple outfalls or a bypass outfall *could* develop a flammable/explosive atmosphere, but that certainly wouldnt be the norm or possible even under faulty conditions...

He said sewer outfall chamber. Whether such is classified hazardous depends on how close to the raw sewage the chamber is in the process.

 

[JFletcher]

He said sewer outfall chamber. Whether such is classified hazardous depends on how close to the raw sewage the chamber is in the process.

Yes, chamber. Vault. Wetwell. Tank of sorts. Outfall tho is at the end of the treatment process, where the clean waste water would go from the contact tanks to the river/bay/ocean. The water at that point is basically as good as tap water and highly unlikely (I dare say impossible) to be able to create a flammable/explosive atmosphere via evolution or production of hydrogen sulfide, methane, etc., which is why I inquired as to if it needed to even be classified. An outfall isnt even Class 1/Division 2 imo.

http://www.cswea.org/WISCONSIN/semi...ar-2013/P Carnahan-2013 NFPA Standard 820.pdf

says "Prominent Treatment Plant Unclassified Locations"

- Plant effluent pumping/conduits and disinfection

Proximity to headworks and solids handling (digesters; classed areas) is typically quite far as most plants gravity flow and thus there is usually substantial real estate between them to have enough elevation drop to allow the water to flow at design levels. At plants I worked at, this would be 300-1000+ feet.

 

[Smart $]

Yes, chamber. Vault. Wetwell. Tank of sorts. Outfall tho is at the end of the treatment process, where the clean waste water would go from the contact tanks to the river/bay/ocean. The water at that point is basically as good as tap water and highly unlikely (I dare say impossible) to be able to create a flammable/explosive atmosphere via evolution or production of hydrogen sulfide, methane, etc., which is why I inquired as to if it needed to even be classified. An outfall isnt even Class 1/Division 2 imo.

http://www.cswea.org/WISCONSIN/semi...ar-2013/P Carnahan-2013 NFPA Standard 820.pdf

says "Prominent Treatment Plant Unclassified Locations"

- Plant effluent pumping/conduits and disinfection

Proximity to headworks and solids handling (digesters; classed areas) is typically quite far as most plants gravity flow and thus there is usually substantial real estate between them to have enough elevation drop to allow the water to flow at design levels. At plants I worked at, this would be 300-1000+ feet.

I'm not in disagreement, but neither one of us did the classification or know the particulars of his situation. He did not even say it was at a WWTP.

 

[Dale001289]

501.15(A)(1)(1)

501.15(A)(1)(1)

In Division 2, a seal would not be required no matter what the conduit entry size. As you have described it, the enclosure isn't required to be explosionproof. See Section 501.10(B)(4). So - if the enclosure isn't required to be explosionproof, a seal isn't required either.

Bob, are there any scenarios in CID1, where an explosion proof junction box containing ONLY terminal strips (in this case, a Nema 7 JB with instrumentation wiring) without arcing devices would require a conduit seal at the enclosure?

Thanks

 

[nhee2]

Bob, are there any scenarios in CID1, where an explosion proof junction box containing ONLY terminal strips (in this case, a Nema 7 JB with instrumentation wiring) without arcing devices would require a conduit seal at the enclosure?

Thanks

If the conduit is larger than 2" it needs a seal. 501.15(A)(1)(2)