rafarrh
Member
- Location
- Caracas, Miranda, Venezuela
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
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