514.8 Underground Wiring.
Code Change Summary: Revisions were made to the type of nonmetallic raceways permitted for motor vehicle fueling facilities.
High Density Polyethylene conduit (Type HDPE) is now permitted for underground wiring below the surface of a Class I, Division 1 or a Class I, Division 2 location at motor vehicle fueling facilities.
The general rule in 514.8 specifies that underground wiring must be installed in threaded rigid metal conduit or threaded steel intermediate metal conduit but exceptions 1 and 2 provide additional options.
In the 2014 NEC®, nonmetallic wiring methods used underground for a gas station were limited to PVC and RTRC. In the 2017 NEC®, type HDPE conduit was added. According to exception 2, the same rules must be followed in order to use any of the three allowable nonmetallic wiring methods:
- They must be buried under at least 2 foot of cover.
- Threaded rigid metal conduit or threaded steel intermediate metal conduit shall be used for the last 2 feet of the underground run to emergence or to the point of connection to the aboveground raceway.
- An equipment grounding conductor shall be included to provide electrical continuity of the raceway system and for grounding of non–current-carrying metal parts.
The substantiation to allow Type HDPE is that it provides at least the same level of protection as Type PVC or Type RTRC when buried 24 inches in the earth. A similar change occurred in 501.10(A)(1).
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 2017 NEC® edition of NFPA 70.
2014 Code Language:
514.8 Underground Wiring. Underground wiring shall be installed in threaded rigid metal conduit or threaded steel intermediate metal conduit. Any portion of electrical wiring that is below the surface of a Class I, Division 1 or a Class I, Division 2 location [as classified in Table 514.3(B)(1) and Table 514.3(B)(2)] shall be sealed within 3.05 m (10 ft) of the point of emergence above grade. Except for listed explosion-proof reducers at the conduit seal, there shall be no union, coupling, box, or fitting between the conduit seal and the point of emergence above grade. Refer to Table 300.5.
Exception No. 1: Type MI cable shall be permitted where it is installed in accordance with Article 332.
Exception No. 2: Type PVC conduit and Type RTRC conduit shall be permitted where buried under not less than 600 mm (2 ft) of cover. Where Type PVC conduit or Type RTRC 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.
2017 Code Language:
514.8 Underground Wiring. Underground wiring shall be installed in threaded rigid metal conduit or threaded steel intermediate metal conduit. Any portion of electrical wiring that is below the surface of a Class I, Division 1 or a Class I, Division 2 location [as classified in Table 514.3(B)(1) and Table 514.3(B)(2)] shall be sealed within 3.05 m (10 ft) of the point of emergence above grade. Except for listed explosion-proof reducers at the conduit seal, there shall be no union, coupling, box, or fitting between the conduit seal and the point of emergence above grade. Refer to Table 300.5.
Exception No. 1: Type MI cable shall be permitted where it is installed in accordance with Article 332.
Exception No. 2: 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.