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nerally 6 inches. Information concerning installation and application of this type of coupling can be obtained from manufacturers’ instructions. Expansion fittings are seldom used underground, where temperatures are relatively constant. If PVC conduit is buried or covered immediately, expansion an...

nerally 6 inches. Information concerning installation and application of this type of coupling can be obtained from manufacturers’ instructions. Expansion fittings are seldom used underground, where temperatures are relatively constant. If PVC conduit is buried or covered immediately, expansion and contraction are not considered a problem. See also 300.7(B) and its enhanced content regarding the expansion of PVC. Earth Movement. Expansion fittings for underground runs of direct buried PVC conduit emerging from the ground shall be provided above grade when required to compensate for earth settling or movement, including frost heave. Informational Note: See 300.5(J). 352.46 Bushings. Where a conduit enters a box, fitting, or other enclosure, a bushing or adapter shall be provided to protect the wire from abrasion unless the box, fitting, or enclosure design provides equivalent protection. Informational Note: See 300.4(G) for the protection of conductors 4 AWG and larger at bushings. 352.48 Joints. All joints between lengths of conduit, and between conduit and couplings, fittings, and boxes, shall be made by an approved method. 352.56 Splices and Taps. Splices and taps shall be made in accordance with 300.15. 352.60 Grounding. Where equipment grounding is required, separate grounding conductor shall be installed in the conduit. Exception No. 1: The equipment grounding conductor shall be permitted to be run separately from the circuit conductors as permitted in 250.134, Exception No. 2, for dc circuits and 250.134, Exception No. 1, for separately run equipment grounding conductors. Exception No. 2: The equipment grounding conductor shall not be required where the grounded conductor is used to ground equipment as permitted in 250.142. Part III. Construction Specifications 352.100 Construction. PVC conduit shall be made of rigid (nonplasticized) polyvinyl chloride (PVC). PVC conduit and fittings shall be composed of suitable nonmetallic material that is resistant to moisture and chemical atmospheres. For use aboveground, it shall also be flame retardant, resistant to impact and crushing, resistant to distortion from heat under conditions likely to be encountered in service, and resistant to low temperature and sunlight effects. For use underground, the material shall be acceptably resistant to moisture and corrosive agents and shall be of sufficient strength to withstand abuse, such as by impact and crushing, in handling and during installation. Where intended for direct burial, without encasement in concrete, the material shall also be capable of withstanding continued loading that is likely to be encountered after installation. 352.120 Marking. Each length of PVC conduit shall be clearly and durably marked at least every 3 m (10 ft) as required in the first sentence of 110.21(A). The type of material shall also be included in the marking unless it is visually identifiable. For conduit recognized for use aboveground, these markings shall be permanent. For conduit limited to underground use only, these markings shall be sufficiently durable to remain legible until the material is installed. Conduit shall be permitted to be surface marked to indicate special characteristics of the material. Informational Note: Examples of these markings include but are not limited to “limited smoke” and “sunlight resistant.