On large jobs with miles of underground conduit, the electrical inspector fully expects to be called for several underground electrical inspections on different days. The electrical inspector will usually inspect and approve a portion of the underground conduit inspection and mark the city approved plans with which areas are approved to cover. For smaller jobs, the inspector might want to come for only one underground conduit inspection after all electrical conduits are installed for the entire project.

Before requesting only a portion of the underground electrical conduit to be inspected, make sure to find out if this is ok with the inspector. If the permit fee for the project was small, it is likely that the city didn’t plan to come out several times just to see 50 total foot of underground conduit. One of the determining factors for the price of the electrical permit is how many times the city thinks they will be called out for an inspection.

Before the underground inspection, make sure following is ready:

• Trench and conduit at proper burial depth per NEC^® Table 300.5
• Trench left open and not covered
• Conduit or cables are suitable for wet location or direct burial
• Conduit or cables are in place and sized according to the plans
• Proper conduit fittings used and properly installed
• Acceptable backfill materials are present with no large rocks per NEC^® 300.5(F)

Never cover the underground electrical installation until approved by the inspector. During the underground electrical inspection, the inspector is looking for proper burial depth which can only be seen when the trench is still open. Sometimes the inspector will give permission beforehand to cover a 20-foot section that hasn’t been inspected yet so that construction equipment and trucks can continue to cross the high traffic areas of the job site.

Below is a preview of the NEC^® (NFPA 70). See the actual NEC^® text at NFPA.ORG for the complete code section. Once there, click on their link to free access to the edition of the NEC^® being enforced.

NEC 300.5(F) Backfill. Backfill that contains large rocks, paving materials, cinders, large or sharply angular substances, or corrosive material shall not be placed in an excavation where materials may damage raceways, cables, conductors, or other substructures or prevent adequate compaction of fill or contribute to corrosion of raceways, cables, or other substructures.

Where necessary to prevent physical damage to the raceway, cable, or conductor, protection shall be provided in the form of granular or selected material, suitable running boards, suitable sleeves, or other approved means.