NEC Questions and Answers based on 2017 NEC - February 2019

Figure 01

Here's the follow-up to yesterday's newsletter.
This includes the answers to the questions sent, so you can see how you did.

Note: The answers to these questions are based on the 2017 NEC. Underlined text indicates a change in the rule for the 2017 NEC.

Q1. What uses are permitted for PVC conduit by the NEC?
A1. Some common uses for Type PVC (polyvinyl chloride) conduit are as follows:

Informational Note: In extreme cold, PVC conduit can become brittle, and is more susceptible to physical damage.

Concealed. PVC conduit can be concealed within walls, floors, or ceilings, directly buried or embedded in concrete in buildings of any height [352.10(A)]. Figure 01

Corrosive Influences. PVC conduit is permitted in areas subject to severe corrosion for which the material is specifically approved by the authority having jurisdiction [352.10(B)].

Author's Comment:
• If subject to exposure to chemical solvents, vapors, splashing, or immersion, materials or coatings must either be inherently resistant to chemicals based upon their listing, or be identified for the specific chemical reagent [300.6(C)(2)].

Wet Locations. PVC conduit is permitted in wet locations such as dairies, laundries, canneries, car washes, and other areas frequently washed or in outdoor locations. Support fittings such as straps, screws, and bolts must be made of corrosion-resistant materials or must be protected with a corrosion-resistant coating, in accordance with 300.6(A) [352.10(D)].

Dry and Damp Locations. PVC conduit is permitted in dry and damp locations, except where limited in 352.12 [352.10(E)].

Exposed. PVC conduit is permitted to be used for exposed work. PVC conduit used in an area subject to physical damage must be identified for the application [352.10(F)].

Author's Comment:
• Schedule 40 PVC conduit is permitted for exposed locations where not subject to physical damage.

Informational Note: Schedule 80 PVC conduit is identified for use in areas subject to physical damage.

Underground. PVC conduit installed underground must comply with the burial requirements of 300.5 [352.10(G)].

Support of Conduit Bodies. PVC conduit can support nonmetallic conduit bodies that aren't larger than the largest trade size of an entering raceway. These conduit bodies can't support luminaires or other equipment and are not permitted to contain devices other than splicing devices permitted by 110.14(B) and 314.16(C)(2) [352.10(H)].

Q2. What uses are not permitted for PVC conduit by the NEC?
A2. PVC conduit is not permitted to be used in the following locations:

Hazardous Locations. PVC conduit isn't permitted to be used in hazardous locations except as permitted by 501.10(A)(1)(a) Ex, 503.10(A), 504.20, 514.8 Ex 2, and 515.8. In Class I, Division 2 locations, except as permitted in 501.10(B)(7). [352.12(A)]

Support of Luminaires. PVC conduit isn't permitted to be used for the support of luminaires or other equipment not described in 352.10(H) [352.12(B)].

Author's Comment:
• PVC conduit can support conduit bodies in accordance with 314.23(E) Ex.

Physical Damage. PVC conduit isn't permitted to be installed if subject to physical damage, unless identified for the application.

Author's Comment:
• Schedule 40 PVC conduit is not identified for use where subject to physical damage. PVC Schedule 80 conduit is identified for use in areas subject to physical damage [352.10(F) Informational Note].

Ambient Temperature. PVC conduit isn't permitted to be installed if the ambient temperature exceeds 50°C (122°F) [352.12(D)].

Q3. What are the minimum and maximum trade sizes allowed by the Code for PVC conduit?
A3. Type PVC conduit smaller than trade size ½ isn't permitted to be used. Type PVC conduit larger than trade size 6 isn't permitted to be used. [352.20].

Q4. What is the maximum number of conductors allowed by the Code to be installed in PVC conduit?
A4. Raceways must be large enough to permit the installation and removal of conductors without damaging the conductors' insulation, and the number of conductors must not exceed that permitted by the percentage fill specified in Chapter 9, Table 1 [352.22].

When all conductors within a raceway are the same size and insulation, the number of conductors permitted can be found in Annex C for the raceway type [Chapter 9, Notes to Tables (1)].

Author's Comment:

• Schedule 80 PVC conduit has the same outside diameter as Schedule 40 PVC conduit, but the wall thickness of Schedule 80 PVC conduit is greater, which results in a reduced interior area for conductor fill.

Author's Comment:
• See 300.17 for additional examples on how to size raceways when conductors aren't all the same size.

Cables can be installed in Type PVC conduit, if the number of cables doesn't exceed the allowable percentage fill specified in Chapter 9, Table 1.

Q5. What are the Code rules for field bends made in a run of PVC conduit?
A5. Raceway bends aren't permitted to be made in any manner that would damage the raceway, or significantly change its internal diameter (no kinks). Field bends must be made only with identified equipment. The radius of the curve of the inner edge of any field bend isn't permitted to be less than shown in Chapter 9, Table 2 [352.24].

Author's Comment:
• Be sure to use equipment designed for heating the nonmetallic raceway so it's pliable for bending (for example, a hot box). Don't use open-flame torches.

To reduce the stress and friction on conductor insulation, the total amount of bends (including offsets) between pull points must not exceed 360° [352.26].