511.8 Underground Wiring Below Class I Locations.
Code Change Summary: Revised section title clarifies the wiring requirements below a Class I location.
Section 511.8 was new in the 2017 NEC® and was an attempt to require specific underground wiring methods below a Class I location in a commercial repair garage.
Left alone, the title of the 2017 section led code readers to apply the strict wiring methods to other underground wiring that may be related to a commercial repair garage but installed outside of the hazardous location. Not all areas of a commercial repair garage are in a hazardous location. Many repair garages have an interior office and waiting room for those having their car serviced. These areas (if properly separated) are not in a hazardous location.
Section 511.7 applies to “Wiring in spaces above Class I locations”. It makes sense to clarify that 511.8 applies to wiring below the Class I location.
Below is a preview of the NEC®. See the actual NEC® text at NFPA.ORG for the complete code section. Once there, click on their link to free access to the 2020 NEC® edition of NFPA 70.
2017 Code Language:
511.8 Underground Wiring. Underground wiring shall be installed in threaded rigid metal conduit or intermediate metal conduit.
Exception: Type PVC conduit, Type RTRC conduit, and Type HDPE conduit shall be permitted where buried under not less than 600 mm (2 ft) of cover. Where Type PVC conduit, Type RTRC conduit, or Type HDPE conduit is used, threaded rigid metal conduit or threaded steel intermediate metal conduit shall be used for the last 600 mm (2 ft) of the underground run to emergence or to the point of connection to the aboveground raceway, and an equipment grounding conductor shall be included to provide electrical continuity of the raceway system and for grounding of non–current-carrying metal parts.
2020 Code Language:
511.8 Underground Wiring Below Class I Locations. Underground wiring shall be installed in threaded rigid metal conduit or intermediate metal conduit.
Exception: Type PVC conduit, Type RTRC conduit, and Type HDPE conduit shall be permitted where buried under not less than 600 mm (2 ft) of cover. Where Type PVC conduit, Type RTRC conduit, or Type HDPE conduit is used, threaded rigid metal conduit or threaded steel intermediate metal conduit shall be used for the last 600 mm (2 ft) of the underground run to emergence or to the point of connection to the aboveground raceway, and an equipment grounding conductor shall be included to provide electrical continuity of the raceway system and for grounding of non–current-carrying metal parts.