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Friday, May 3, 2019
Question:
Hello – we have multiple opinions from superintendents and PM’s on a project that we are hoping to get clarification on. I have attached pictures to help this email make sense. Floor outlets were missed and discovered after the post tension slab was poured. The electrician had a channel chipped out in the concrete and placed the conduit in it allowing for 0 cover at the top of the conduit. It is our understanding of NEC Code 300.5 note 2 that this is in a concrete trench the conduit needs 2in of cover. One Project Manager is stating that this is under roof, which means it is “Under Building” and code 300.5 note 3 applies, so a “0” cover is acceptable. We interpret under building to mean under the slab, not under the roof in this case. I am hoping you can help clarify this for us, so we can move forward. We appreciate any knowledge you can share about this issue.
Thank you, JESSICA MONROY
A
Answer:
Hey Jessica thanks for your question. The title of 300.5 is Unground Installations, if your installation is not underground then none of 300.5 applies. Under a building roof is within a building, not necessarily under a building. Also notice that under a building in Row 3 of Table 300.5 requires 0 cover with no mention of a slab, it can be a "dirt" floor. Note 2 to that table applies to raceways that are not suitable for direct burial then 2-inch encasement is required. The rules in 300.4 apply for protection from physical damage and can vary depending on the type of wiring method used. If using Rigid PVC conduit, it must be identified for physical damage - if located in such an area as stated in 352.10(F). The AHJ will need to determine if that is an issue in your example but no cover depth is necessary. Raceways are also often installed on the surface of buildings and structures. The structural integrity of the concrete being "chipped out" is a separate issue and outside the NEC scope but should be discussed with the building official or civil/structural engineer.