Sealing at Class I, Div. 2 boundary discussion

[rafarrh]

Hello everyone. I'm an electrical engineer and currently I am taking a graduate course on electrical installations and as part of an academic exercise our teacher asked us to design, according to NEC Art. 501, the installation assembly to enter an electrical control box containing arcing devices such as pushbuttons, pilot lights and a combination switch and starter. This box is located outdoors on a Class I, Div. 2 area. It was also asked to specify the enclosure of such box. The conduit entering the box comes from a conduit stub-up located directly below the box.

First I said that the box shall be identified for Class 1, Div. 1 location (2011 NEC Art. 501.115(B)(1)) and specified an explosionproof enclosure (2011 NEC Art. 501.105(A)). To comply with NEC Article 501.15(B)(1) I placed an explosionproof male-female union on the hub of the box followed by an explosionproof seal within the 18 inches from the enclosure.

Since the conduit entering the box comes from a conduit stub-up it might be consider that the finished grade or paving represents the boundary of the classified location, so I placed a second seal there to comply with NEC Art. 501.15(B)(2). So if you?re still here with me my design would be something like the one on the left of the drawing.

The teacher said that the second seal at the bottom was not necessary because the one that?s closer to the enclosure is less than 10 feet to the boundary of the classified location as NEC Art. 501.15(B)(2), which is actually true, and instead he proposed another design shown on the right.

I told him that even when the first seal is less than 10 feet from the boundary that design does not comply with the second part of the article that says: ??Except for listed reducers at the conduit seal, there shall be no union, coupling, box, or fitting between the conduit seal and the point at which the conduit leaves the Division 2 location?? which in this case is the ground or finished grade.

So we started an argument that went on and on for several minutes but neither one of us convinced the other, so I said we must turn to the experts. so, what do you think? Which design really meets the requirements of the Code? What?s your verdict?

Thanks for reading and for all your answers.





View attachment Dise?o.pdf

 

[Smart $]

Both are compliant.

For installation pictured on right, see 501.15(B)(2) Exception No. 4. and condition (4) therein.

Based on the assumption below grade is an unclassified location.

 

[don_resqcapt19]

There is nothing in the code to suggest that a single seal cannot serve two purposes as long as the installation of the seal meets the requirements for both purposes.

However the coupling above the surface of the concrete on the right drawing means that it is impossible to make a code compliant installation no matter how many seals are installed.

501.15(B)(2) ... The conduit run between the conduit seal and the point at which the conduit leaves the Division 2 location shall
contain no union, coupling, box, or other fitting except for a listed explosionproof reducer installed at the conduit seal.

 

[Smart $]

There is nothing in the code to suggest that a single seal cannot serve two purposes as long as the installation of the seal meets the requirements for both purposes.

However the coupling above the surface of the concrete on the right drawing means that it is impossible to make a code compliant installation no matter how many seals are installed.

Good catch!

 

[nhee2]

I would have said that the second seal is required due to the union located in the above ground section, but after reading the exception referenced by smart, I think that only the single seal would be required - assuming the UG section is nonclassified.

 

[nhee2]

Actually I change my mind - I think the second seal is required - item 4 in exception 4 says 'contains only threaded metal conduit, unions, couplings, conduit bodies, and fittings in the unclassified location'.

The fitting which forces the second seal to be required (in my opinion) is in the classified location.

 

[Smart $]

Actually I change my mind - I think the second seal is required - item 4 in exception 4 says 'contains only threaded metal conduit, unions, couplings, conduit bodies, and fittings in the unclassified location'.

The fitting which forces the second seal to be required (in my opinion) is in the classified location.

That's correct. Even if the coupling at grade was omitted, the union would require a second seal placed above grade and below the union.

What I was thinking just before I made my first post saying both were compliant was why is there a union there??? Another one to chalk up to not following my gut instinct. :ashamed:

 

[rafarrh]

Both are compliant.

For installation pictured on right, see 501.15(B)(2) Exception No. 4. and condition (4) therein.

Based on the assumption below grade is an unclassified location.

Hi, Smart $, Thanks for your reply.

I checked 501.15(B)(2) Exception No. 4. and condition (4), and I think that precise condition isn't met. It clearly says: ?The conduit system segment contains only threaded metal conduit, unions, couplings, conduit bodies, and fittings in the unclassified location?.
In the picture on the right the union and the RSG coupling are above grade, i.e, in the classified area.

The explosionproof union is not design to avoid the passage of vapor and gases from the classified location to the inside of the conduit and from there to the unclassified location, and neither the RSG coupling, which is the purpose of installing the second seal.

I think this makes the design on the right non compliant. To met that condition the conduit should run straight from the first seal to the unclassified location, below grade, which makes its constructability a lot harder.

 

[rafarrh]

Both are compliant.

For installation pictured on right, see 501.15(B)(2) Exception No. 4. and condition (4) therein.

Based on the assumption below grade is an unclassified location.

Hi, Smart $, Thank you very for your reply.

I checked 501.15(B)(2) Exception No. 4. and condition (4), and I think that precise condition isn't met. It clearly says: ?The conduit system segment contains only threaded metal conduit, unions, couplings, conduit bodies, and fittings in the unclassified location?.

In the picture on the right the union and the RSG coupling are above grade, i.e, in the classified area.

The explosionproof union is not design to avoid the passage of vapor and gases from the classified location to the inside of the conduit and from there to the unclassified location, and neither the RSG coupling, which is the purpose of installing the second seal.

 

[rafarrh]

Hi, Smart $, Thank you very for your reply.

I checked 501.15(B)(2) Exception No. 4. and condition (4), and I think that precise condition isn't met. It clearly says: ?The conduit system segment contains only threaded metal conduit, unions, couplings, conduit bodies, and fittings in the unclassified location?.

In the picture on the right the union and the RSG coupling are above grade, i.e, in the classified location.

The explosionproof union is not design to avoid the passage of vapor and gases from the classified location to the inside of the conduit and from there to the unclassified location, and neither the RSG coupling, which is the purpose of installing the second seal.

 

[rbalex]

• The left diagram with or without the lower seal would be fine if the conduit was run from grade to the seal.
• The right diagram fails with the union between the seal and grade.
• Section 501.15(B)(2) Exception No. 4 requires all five conditions [(1) through (5)] to be met. It was originally developed to permit long runs in pipeways that may run through multiple Division 2 envelopes; i.e., the entire run is outdoor, aboveground. [Condition (2)]

 

[rafarrh]

And what about without the union?

And what about without the union?

• The left diagram with or without the lower seal would be fine if the conduit was run from grade to the seal.
• The right diagram fails with the union between the seal and grade.
• Section 501.15(B)(2) Exception No. 4 requires all five conditions [(1) through (5)] to be met. It was originally developed to permit long runs in pipeways that may run through multiple Division 2 envelopes; i.e., the entire run is outdoor, aboveground. [Condition (2)]

Hi rbalex, thanks for your reply.

I got another question for you.

Let's say that the union on the left diagram is like the one on the right, i.e., between the upper seal and the enclosure.

Wouldn't you think that the design still fails with the RSG coupling above grade (well half of it) in the classified location? As NEC Art. 501.15(B)(2) says: ??Except for listed reducers at the conduit seal, there shall be no union, coupling, box, or fitting between the conduit seal and the point at which the conduit leaves the Division 2 location??

 

[rbalex]

...

Let's say that the union on the left diagram is like the one on the right, i.e., between the upper seal and the enclosure.
...

Your new scenario statement is a bit confusing to me. To clarify, the diagram on the left has the union between the enclosure and the seal AND there is NO coupling at grade. With or without the lower seal that installation is acceptable.

• Moving the union to below the seal would be a violation, with or without the coupling at grade.
• Moving the union to below the seal is a terrible design. It would cause problems if the panel needed to be removed.
• A coupling "(well half of it) in the classified location" would be a violation.
• A coupling set flush with grade is debatable.

The last statement may be confusing to you. However, "You gotta draw the line somewhere." For a judiciously selected boundary, a coupling located entirely in the unclassified location, i.e., below grade, is technically acceptable.

NOTE: Code Making Panel 14 (CMP14) has been trying to eliminate Class I, Division 2/unclassified boundary seals for many Code cycles. That was the original reason for Section 501.15(B)(2) Exception No. 4. They are now at the point that Class I, Division 2/unclassified boundary seals aren't required to be explosionproof at all. Many CMP14 members would eliminate such boundary seals altogether, but it takes a 2/3 majority to do so.​

 

[rafarrh]

Your new scenario statement is a bit confusing to me. To clarify, the diagram on the left has the union between the enclosure and the seal AND there is NO coupling at grade. With or without the lower seal that installation is acceptable.

• Moving the union to below the seal would be a violation, with or without the coupling at grade.
• Moving the union to below the seal is a terrible design. It would cause problems if the panel needed to be removed.
• A coupling "(well half of it) in the classified location" would be a violation.
• A coupling set flush with grade is debatable.

The last statement may be confusing to you. However, "You gotta draw the line somewhere." For a judiciously selected boundary, a coupling located entirely in the unclassified location, i.e., below grade, is technically acceptable.

NOTE: Code Making Panel 14 (CMP14) has been trying to eliminate Class I, Division 2/unclassified boundary seals for many Code cycles. That was the original reason for Section 501.15(B)(2) Exception No. 4. They are now at the point that Class I, Division 2/unclassified boundary seals aren't required to be explosionproof at all. Many CMP14 members would eliminate such boundary seals altogether, but it takes a 2/3 majority to do so.​

Ooops, my mistake. When I said left I meant right, it must be because the diagram on the left is the one that's right hehe.

But you did answer my question anyway. I just wanted to make sure that not only the union below the seal in the diagram on the right side made it violate the Code but also the half RSG coupling sticking out in the classfied area.

Thanks for answering rbalex and for that info on the NOTE as well. But today as it is, the diagram on the right is Code violating.