All references are based on the 2011 edition of the NEC.
According to Sec. 362.10, electrical nonmetallic tubing (ENT) is permitted to be used in nine specific applications, two of which include: “Encased in poured concrete, or embedded in a concrete slab on grade when ENT is placed on sand or approved screenings, provided fittings identified for this purpose are used for connections;” and “For wet locations indoors as permitted in this section or in a concrete slab on or below grade, with fittings listed for the purpose.” However, as noted in 362.12(4), ENT is not permitted to be buried directly in the earth.
As a side note, we can see the ENT below is connected to the PVC box with a PVC connector. According to 362.48, “All joints between lengths of tubing and between tubing and couplings, fittings, and boxes shall be by an approved method.” Although ENT fittings are available, in general, PVC fittings of the same size as the ENT may be used, provided that the correct solvent cement is used to join them. ENT solvents may have a brush applicator instead of a dauber type of applicator. But let’s be clear on this fact. Even if the correct fittings and cement were used here, it is still a violation to bury ENT in the dirt.
This 4-in.-sq box is recessed into the plywood subfloor. This is a clear violation of 314.27(B) [Floor Boxes], which states, “Boxes listed specifically for this application shall be used for receptacles installed in the floor.” The box is also being secured by staples designed for securing NM cables. This is a violation of 314.23(C), which requires that clamps, anchors, or fittings identified for this purpose be used for securing the box. NM cable staples are not identified for securing boxes. If a person accidentally stepped on this box, it could very well go crashing through the floor, because it is only held in place by the “old work” ears attached to the box. The missing cover plate is also a violation of 406.6, which requires faceplates be installed to completely cover the opening and seat against the mounting surface.
One positive thing I would like to point out is the barrier separating the communication circuit from the power circuit in the box. Section 800.133(A)(1)(d) states in part, “Communications conductors shall not be placed in any raceway, compartment, outlet box, junction box, or similar fitting with conductors of electric light or power circuits.” However, Exception No. 1 of this rule states, “where all of the conductors of electric light or power circuits are separated from all of the conductors of communications circuits by a permanent barrier or listed divider.”