Lesson 46 –  PVC and Nonmetallic Raceways

Article 352 — Rigid Polyvinyl Chloride Conduit

Article 352 covers rigid polyvinyl chloride conduit and its associated installation requirements. Like the metallic raceway articles studied previously, Article 352 includes permitted uses, prohibited uses, securing and supporting, bends, fittings, expansion provisions, and other requirements specific to the wiring method.

Why PVC Is Used

PVC conduit has physical and electrical characteristics that make it particularly useful in environments where metallic raceway may require additional corrosion protection or where a nonconductive wiring method is desirable.

PVC Is Not Limited to Underground Work

A common misconception is that PVC conduit is only an underground wiring method. Article 352 permits PVC in a variety of applications, including concealed work, dry and damp locations, wet locations, exposed work where permitted, corrosive environments where suitable, and underground installations.

The installation conditions determine the type of PVC, physical protection, supports, fittings, conductor requirements, and other provisions that must be applied.

Schedule 40 and Schedule 80

PVC conduit is manufactured in different wall thicknesses. Schedule 40 and Schedule 80 are the two designations most commonly encountered in electrical work. Schedule 80 has a thicker wall and greater mechanical strength than Schedule 40 of the same nominal trade size.

Schedule 40 PVC is commonly used where the conduit is not subject to physical damage. Where PVC conduit is exposed to physical damage, the raceway must be identified for that application. Schedule 80 PVC is commonly identified for locations subject to physical damage.

PVC Below Grade

PVC conduit is extensively used underground because it is resistant to moisture and soil-related corrosion. Underground installations must comply not only with Article 352 but also with the applicable requirements of NEC 300.5.

Article 300.5 addresses issues including minimum cover, protection where raceways emerge from grade, wet-location conditions, underground transitions, and protection from movement or physical damage.

PVC Support Spacing Depends on Raceway Size

NEC 352.30 requires PVC conduit to be securely fastened and supported while permitting the raceway to move as necessary because of thermal expansion and contraction. PVC must generally be securely fastened within 3 feet of boxes, cabinets, conduit bodies, or other termination fittings.

The maximum spacing between supports is found in Table 352.30. The permitted distance changes with raceway trade size, which means there is no single support interval that applies to all PVC conduit.

PVC Expands and Contracts

PVC changes length significantly as its temperature changes. A long raceway installed outdoors can experience substantial movement between cold and hot conditions, especially where it is exposed to direct sunlight or large seasonal temperature swings.

If the ends of a long PVC run are rigidly fixed without allowing for this movement, the raceway can bow, pull apart fittings, damage boxes, or place excessive stress on supports and terminations.

Article 352.44

Article 352 contains specific requirements for accommodating expansion and contraction of PVC conduit. Where a straight run between securely mounted items is expected to experience sufficient length change, an expansion fitting is required.

The applicable expansion information is determined using the NEC provisions and Table 352.44. On the exam, pay attention to the total raceway length, temperature range, and whether the ends of the raceway are restrained.

Transitions From Underground to Above Grade

PVC raceway emerging from the earth can be affected by soil settlement, frost heave, and other earth movement. This can impose substantial stress on the raceway and the equipment or enclosure to which it is connected.

Article 300.5 and the applicable Article 352 requirements must be considered where movement could damage the raceway. An underground-to-above-grade transition is therefore more than simply gluing a vertical piece of PVC onto a buried horizontal run.

Fittings and Solvent-Cemented Connections

PVC raceway sections are commonly joined using listed couplings and fittings with the joining method specified for the raceway system. Proper preparation and assembly are important because the completed fitting must maintain mechanical strength and raceway continuity.

Field Bends and Factory Elbows

PVC raceway can be installed with factory elbows and can also be field bent using methods appropriate for the product. A field bend must not damage, flatten, burn, kink, or otherwise impair the raceway.

As with other raceways, the finished bend must maintain adequate internal space for conductors and comply with the applicable bending-radius and total-bend limitations.

PVC Does Not Provide a Fault-Current Path

Unlike EMT, IMC, and RMC, PVC conduit is nonconductive and cannot serve as an equipment grounding conductor. Where equipment grounding is required, a wire-type or other NEC-recognized equipment grounding conductor must be provided with the circuit as applicable.

Metal boxes, cabinets, equipment enclosures, fittings, and other conductive components connected to a PVC raceway system still require grounding and bonding. The absence of a metallic raceway makes the separate equipment grounding path especially important.

Conductor Selection Inside PVC

PVC itself may be suitable for wet environments, but that does not change the rating required for the conductors inside it. Raceway systems installed underground and raceways in qualifying wet locations can contain moisture or condensation.

Conductors installed in these locations must therefore be listed for wet-location use. Common examples include conductors carrying a THWN-2 or XHHW-2 designation, depending on the specific conductor and application.

Nonmetallic Does Not Mean Indestructible

PVC is resistant to many corrosive environments, but it is not automatically suitable for every chemical exposure. Article 352 requires the raceway to be suitable for corrosive influences to which it will be exposed.

Chemicals, extreme temperatures, mechanical impact, ultraviolet exposure, and other conditions can affect the raceway or its fittings. Always evaluate the actual environment rather than assuming that a nonmetallic raceway cannot be damaged.

Beyond Rigid PVC

Chapter 3 contains other nonmetallic wiring methods in addition to rigid PVC conduit. These systems have different construction, applications, and installation rules.

The presence of several nonmetallic raceway types reinforces an important exam principle: identify the exact wiring method before applying its permitted-use, support, fill, grounding, or installation requirements.

Work From the Installation Conditions

PVC questions often combine several requirements in one problem. The question may describe an underground run that emerges above grade, passes through an area subject to physical damage, experiences a large temperature change, and terminates at metal equipment.

Code Locations to Know

Key Points to Remember

• Rigid PVC conduit is covered by NEC Article 352.
• PVC is permitted in many above-ground as well as underground applications.
• PVC can be used in concealed, dry, damp, wet, exposed, corrosive, and underground installations when the applicable requirements are satisfied.
• Schedule 40 and Schedule 80 have different wall thicknesses and physical-protection capabilities.
• PVC exposed to physical damage must be identified for that application.
• Schedule 80 PVC is commonly identified for areas subject to physical damage.
• Underground PVC installations are also subject to NEC 300.5.
• The interior of underground raceways is considered a wet location.
• Conductors installed underground in PVC must therefore be suitable for wet locations.
• PVC must generally be secured within 3 feet of boxes, cabinets, conduit bodies, and other termination fittings.
• PVC support spacing varies according to raceway trade size and must be determined from Table 352.30.
• PVC expands and contracts substantially with temperature changes.
• Expansion fittings or other required provisions must accommodate expected raceway movement.
• Supports must permit the thermal movement necessary for the expansion system to function.
• Underground-to-above-grade transitions must account for physical protection and possible earth movement.
• PVC is nonconductive and cannot itself serve as an equipment grounding conductor.
• A separate NEC-recognized equipment grounding path must be provided where required.
• Metal boxes and equipment connected to PVC raceway still require grounding and bonding.
• ENT, LFNC, RTRC, and other nonmetallic raceways have separate NEC requirements and should not automatically be treated as PVC.