On an underground installation can I just backfill the trench and leave "sight tubes" or "view tubes" in the trench for the inspector to use for his inspection?

The use of sight tubes or view tubes is limited to the discretion and permission of the field inspector and then only under very unique and specific job site conditions. The only practical function of these tubes is to attempt to show an inspector that the covered wiring method is installed at the proper depth. It should be obvious that there isnt much to see or view when youre looking down a 2 or 3 piece of pipe stuck in the ground! Also, an underground inspection is not only about depth. During the course of an underground inspection, in addition to checking the depth, the proper wiring method is determined. For example, on direct burial installations, verification is made that conductors suitable for direct burial are installed and that the proposed fill will not damage the conductors. On conduit installations, the type of conduit installed, the proper gluing of joints (PVC), engagement of threads, determining that the conduit has not been damaged during installation (crushed, ...  more