Article 501.10(A)(1) allows PVC conduits no less than 24" below Class 1 Division 1 areas where enveloped in at least 2" of concrete. There are exceptions to the concrete in Fuel Dispensing and Bulk storage. Class 1 Division 2 allows all methods of C1D1 and does not modify the requirement. We have a new RNG facility in which we are running a number of PVC conduits into a C1D2 area. The mechanical/structural engineering firm has the lead and has indicated that concrete encasement is not necessary since the only hazardous substance is lighter than air and the area below the classified area is not classified. Therefore the installation would be more of a boundary crossing scenario. They indicate they have done numerous installations and none have required encasement. This does seem reasonable since there's nothing that would seep down to the conduit. However, that is not exactly what the code says. Am I missing something? I'd rather not require the concrete encasement but I feel compelled based on strict interpretation of the NEC.
You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an alternative browser.
You should upgrade or use an alternative browser.
PVC Under Class 1 DIvision 2 Area
- Thread starter MartStod
- Start date
I believe the exception in 501.10(A)(1) says to comply with 514.8, and 514.8 exception 2 Allows for this installation without concrete encasement so long as the pvc is no less than 24". Anything above 24" needs to be metallic, and with seals.
cpstephens
New User
- Location
- California
- Occupation
- Electrical Engineer
Apologies if I should not "piggyback" on this post but it seemed related.
I am working on a similar installation, it would fall under Article 513, indoors, the building area (above the floor) would be Class 1 Div 2. Conduits installed below the slab, some penetrate into the C1D2 area, others pass completely under it, into unclassified areas.
I am curios to hear other's input/interpretation:
My understanding for the reasoning behind the 24" of cover for PVC requirement, is because haz gases will migrate below grade into the conduit system.For this reason underground areas below C1D2 area typically considered C1D1. Does that imply that the hazardous classification only extends to 24" below grade? What if you had a vapor barrier below the C1D2 area but above the conduit? If the gas is lighter than air as per MartStod's situation above, then the underground area would not be classified and this would impact where seals and what type (explosion proof, or non-explosion proof) are required.
Another more specific example in my situation, what if the PVC conduit was buried, say 36", below the C1D2 area and emerges at both ends in unclassified areas. Would you need boundary seals? Could you consider the conduit had never passed through a classified area?
I am working on a similar installation, it would fall under Article 513, indoors, the building area (above the floor) would be Class 1 Div 2. Conduits installed below the slab, some penetrate into the C1D2 area, others pass completely under it, into unclassified areas.
I am curios to hear other's input/interpretation:
My understanding for the reasoning behind the 24" of cover for PVC requirement, is because haz gases will migrate below grade into the conduit system.For this reason underground areas below C1D2 area typically considered C1D1. Does that imply that the hazardous classification only extends to 24" below grade? What if you had a vapor barrier below the C1D2 area but above the conduit? If the gas is lighter than air as per MartStod's situation above, then the underground area would not be classified and this would impact where seals and what type (explosion proof, or non-explosion proof) are required.
Another more specific example in my situation, what if the PVC conduit was buried, say 36", below the C1D2 area and emerges at both ends in unclassified areas. Would you need boundary seals? Could you consider the conduit had never passed through a classified area?