All references are based on the 2011 edition of the NEC.
Singing the Blues
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.
Four on the Floor
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.”