Aircraft Hangar Underground Wiring

[faresos]

Hello All,

I know this subject has been discussed several times but I still sometimes feel like it's not clear. We have a panelboard installed inside the hangar at the wall. The branch circuits conduits emerged from the slab and is unbroken (no fittings). The length of the vertical conduits rises out the floor and terminating into the bottom of the panelboard are more than 18"AFF. My understanding the area in or below the hangar floor is considered Class I, Div 1 and the area above the floor (up to 18"AFF) is considered Class I, Div 2 (per 513.8), therefor a conduit seal must be provided within 18" of the vertical conduits. However, I was told by the contractor the seal fitting is not required because the vertical conduits is unbroken and longer than 18". My question, do we really need a seal fitting for this installation or not? This panel and conduits are already installed but I thought this installation doesn't meet code requirement. Any thought on this is really appreciated.

 

[rbalex]

I’ve hesitated to answer this because I agree with the contractor, but explaining why is a bit convoluted.

CMP 14 doesn’t have as much control over Articles 511 to 517 as I believe it should. Article 510 explains why, but you can’t find that Article in the 2023 NEC; you need to see an earlier Edition where it explains Articles 511 to 517 are essentially controlled by other Technical Committees. See Section 513.1 IN No. 1 for the external Standard that applies.

Section 513.8 doesn’t actually say below grade is Class I, Division 1; it’s just treated as if it is (wiring methods only). Section 513.3 defines the actual area classifications, not 513.8.

“Classic” underground is unclassified. Usually, only below-grade locations directly open to a classified Class I envelope are classified Class I, Division 1.

Now see Section 501.15(B)(2) Ex No. 1