NEC Section 511-4 requires wiring methods (raceways) installed within or extended through classified locations identified in Section 511-3 to be in compliance with the requirements of Section 501-4. Where any part of a raceway section extends into or through a classified location, including raceways that have segments embedded in a masonry wall or floor, or installed beneath a floor, the complete raceway section must be of a type identified by Section 501-4 along its entire length to an appropriate seal. This requirement prohibits the installation of intervening raceway segments that are not suitable for a location classification that any part of a raceway section enters or passes through, such as a transition from EMT installed within a concrete floor to IMC installed within a classified location above the floor. However, Section 511-4, Exception, allows the installation of rigid nonmetallic conduit for the intervening section of the raceway where buried under not less than 2 feet of cover and rigid metal conduit or IMC is extended from this depth to emergence and subsequent extension to a wiring method complying with Sections 511-4 or 511-6.
Raceways installed in commercial garages that are not within or do not extend through a classified location are not required to be those identified by Section 501-4. Raceways embedded in a masonry wall or floor, or installed beneath the floor and not extended into or through a classified location are not considered to be within a classified location. This allows the installation of rigid nonmetallic conduit within a masonry wall from a termination point above a classified location into or under a floor and emerging from this unclassified location within a masonry wall to an elevation above a classified location or into a nonclassified location without being required to be installed under 2 feet of cover or otherwise installed as a wiring method located within a classified location. The encasement of a raceway within a concrete curb such that the raceway is encased by a minimum of 2 inches of solid masonry or concrete that extends to the classified location boundary is an acceptable means to isolate a raceway from an adjoining classified location. The area beneath the floor or pit within a commercial garage is not a classified location, although each floor level of a commercial garage may have associated classified locations.
Sealing of raceways is required at both vertical and horizontal boundaries of defined Class I locations in accordance with Section 501-5. Section 501-5(a)(4), Exception, and Section 501-5(b)(2), Exception No. 1, provide that conduit seals shall not be required where unbroken (without fitting) lengths of rigid metal conduit or IMC pass through and extend 12 inches beyond the boundary of a Class I location. This allows the installation of rigid metal conduit or IMC from a point 30 inches above the floor of a commercial garage (12 inches beyond the 18 inch classified location) to a depth of at least 12 inches below the upper surface of the floor, and not re-entering a classified location, to not be required to have sealing fittings installed at the boundaries of the classified location. If this raceway is extended and enters or passes through a classified location at its outer end, the outer segment must either be sealed at the boundaries of the classified location it enters or passes through, or be exempt from the requirement for sealing.