Article 355
Reinforced Thermosetting Resin Conduit: Type RTRC
Part I. General
- Scope. This article covers the use, installation, and construction specification for reinforced thermosetting resin conduit (RTRC) and associated fittings.Informational Note: Refer to Article 352 for Rigid Polyvinyl Chloride Conduit: Type PVC, and Article 353 for High Density Polyethylene Conduit: Type HDPE.
- Definition.
Reinforced Thermosetting Resin Conduit (RTRC). A rigid nonmetallic raceway of circular cross section, with integral or associated couplings, connectors, and fittings for the installa‐ tion of electrical conductors and cables.
355.6 Listing Requirements. RTRC, factory elbows, and asso‐ ciated fittings shall be listed.
Part II. Installation
355.10 Uses Permitted. The use of RTRC shall be permitted in accordance with 355.10(A) through (I).
- Concealed. RTRC shall be permitted in walls, floors, and ceilings.
- Corrosive Influences. RTRC shall be permitted in loca‐ tions subject to severe corrosive influences as covered in 300.6 and where subject to chemicals for which the materials are specifically approved.
- Cinders. RTRC shall be permitted in cinder fill.
- Wet Locations. RTRC shall be permitted in portions of dairies, laundries, canneries, or other wet locations, and in locations where walls are frequently washed, the entire conduit system, including boxes and fittings used therewith, shall be installed and equipped so as to prevent water from entering the conduit. All supports, bolts, straps, screws, and so forth, shall be of corrosion-resistant materials or be protected against corrosion by approved corrosion-resistant materials.
- Dry and Damp Locations. RTRC shall be permitted for use in dry and damp locations not prohibited by 355.12.
- Exposed. RTRC shall be permitted for exposed work if identified for such use.Informational Note: RTRC, Type XW, is identified for areas of physical damage.
- Underground Installations. For underground installa‐ tions, see 300.5 and 300.50.
- Support of Conduit Bodies. RTRC shall be permitted to support nonmetallic conduit bodies not larger than the largest trade size of an entering raceway. These conduit bodies shall not support luminaires or other equipment and shall not contain devices other than splicing devices as permitted by 110.14(B) and 314.16(C)(2).
- Insulation Temperature Limitations. Conductors or cables rated at a temperature higher than the listed temperature rating of RTRC conduit shall be permitted to be installed in RTRC conduit, if the conductors or cables are not operated at a temperature higher than the listed temperature rating of the RTRC conduit.
355.12 Uses Not Permitted. RTRC shall not be used under the following conditions.
- Hazardous (Classified) Locations.
- In any hazardous (classified) location, except as permit‐ ted by other articles in this CodeARTICLE 355 — REINFORCED THERMOSETTING RESIN CONDUIT: TYPE RTRC 355.100
- In Class I, Division 2 locations, except as permitted in 501.10(B)(1)(6)
Trade Size
mm or m
ft16–271∕2–1
900 mm335–5311∕4–2
1.5 m563–7821∕2–3
1.8 m691–12931∕2–5
2.1 m71556
2.5 m8 - Support of Luminaires. For the support of luminaires or other equipment not described in 355.10(H).Table 355.30 Support of Reinforced Thermosetting Resin Conduit (RTRC)
Maximum Spacing Between - Physical Damage. Where subject to physical damage unless identified for such use.
- Ambient Temperatures. Where subject to ambient temperatures in excess of 50°C (122°F) unless listed otherwise.
- Theaters and Similar Locations. In theaters and similar locations, except as provided in 518.4 and 520.5.
355.20 Size.
Conduit Size
Supports
- Minimum. RTRC smaller than metric designator 16 (trade size 1∕2) shall not be used.
- Maximum. RTRC larger than metric designator 155 (trade size 6) shall not be used.
Informational Note: The trade sizes and metric designators are for identification purposes only and do not relate to actual dimensions. See 300.1(C).
355.22 Number of Conductors. The number of conductors shall not exceed that permitted by the percentage fill specified in Table 1, Chapter 9. Cables shall be permitted to be installed where such use is not prohibited by the respective cable arti‐ cles. The number of cables shall not exceed the allowable percentage fill specified in Table 1, Chapter 9.
355.24 Bends — How Made. Bends shall be so made that the conduit will not be damaged and the internal diameter of the conduit will not be effectively reduced. Field bends shall be made only with identified bending equipment. The radius of the curve to the centerline of such bends shall not be less than shown in Table 2, Chapter 9.
355.26 Bends — Number in One Run. There shall not be more than the equivalent of four quarter bends (360 degrees total) between pull points, for example, conduit bodies and boxes.
355.28 Trimming. All cut ends shall be trimmed inside and outside to remove rough edges.
355.30 Securing and Supporting. RTRC shall be installed as a complete system in accordance with 300.18 and shall be securely fastened in place and supported in accordance with 355.30(A) and (B).
- Securely Fastened. RTRC shall be securely fastened within 900 mm (3 ft) of each outlet box, junction box, device box, conduit body, or other conduit termination. Conduit listed for securing at other than 900 mm (3 ft) shall be permitted to be installed in accordance with the listing.
- Supports. RTRC shall be supported as required in Table
355.30. Conduit listed for support at spacing other than as shown in Table 355.30 shall be permitted to be installed in accordance with the listing. Horizontal runs of RTRC suppor‐ ted by openings through framing members at intervals not exceeding those in Table 355.30 and securely fastened within 900 mm (3 ft) of termination points shall be permitted.
355.44 Expansion Fittings. Expansion fittings for RTRC shall be provided to compensate for thermal expansion and contrac‐ tion where the length change, in accordance with Table 355.44,
is expected to be 6 mm (1∕4 in.) or greater in a straight run between securely mounted items such as boxes, cabinets, elbows, or other conduit terminations.
355.46 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 enclo‐ sure design provides equivalent protection.
Informational Note: See 300.4(G) for the protection of conduc‐ tors 4 AWG and larger at bushings.
355.48 Joints. All joints between lengths of conduit, and between conduit and couplings, fitting, and boxes, shall be made by an approved method.
355.56 Splices and Taps. Splices and taps shall be made in accordance with 300.15.
355.60 Grounding. Where equipment grounding is required, a separate equipment grounding conductor shall be installed in the conduit.
Exception No. 1: As permitted in 250.134(B), Exception No. 2, for dc circuits and 250.134(B), Exception No. 1, for separately run equip‐ ment grounding conductors.
Exception No. 2: Where the grounded conductor is used to ground equipment as permitted in 250.142.
Part III. Construction Specifications
355.100 Construction. RTRC 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 encoun‐ tered 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 suffi‐ cient strength to withstand abuse, such as by impact and crush‐ ing, 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.
355.120 ARTICLE 356 — LIQUIDTIGHT FLEXIBLE NONMETALLIC CONDUIT: TYPE LFNC
Table 355.44 Expansion Characteristics of Reinforced Thermosetting Resin Conduit (RTRC) Coefficient of Thermal Expansion = 2.7 × 10–5 mm/mm/°C (1.5 × 10–5 in./in./°F)
Temperature Change (°C) | Length Change of RTRC Conduit (mm/m) | Temperature Change (°F) | Length Change of RTRC Conduit (in./100 ft) | Temperature Change (°F) | Length Change of RTRC Conduit (in./100 ft) | |
| 5 | 0.14 | 5 | 0.09 | 105 | 1.89 | |
| 10 | 0.27 | 10 | 0.18 | 110 | 1.98 | |
| 15 | 0.41 | 15 | 0.27 | 115 | 2.07 | |
| 20 | 0.54 | 20 | 0.36 | 120 | 2.16 | |
| 25 | 0.68 | 25 | 0.45 | 125 | 2.25 | |
| 30 | 0.81 | 30 | 0.54 | 130 | 2.34 | |
| 35 | 0.95 | 35 | 0.63 | 135 | 2.43 | |
| 40 | 1.08 | 40 | 0.72 | 140 | 2.52 | |
| 45 | 1.22 | 45 | 0.81 | 145 | 2.61 | |
| 50 | 1.35 | 50 | 0.90 | 150 | 2.70 | |
| 55 | 1.49 | 55 | 0.99 | 155 | 2.79 | |
| 60 | 1.62 | 60 | 1.08 | 160 | 2.88 | |
| 65 | 1.76 | 65 | 1.17 | 165 | 2.97 | |
| 70 | 1.89 | 70 | 1.26 | 170 | 3.06 | |
| 75 | 2.03 | 75 | 1.35 | 175 | 3.15 | |
| 80 | 2.16 | 80 | 1.44 | 180 | 3.24 | |
| 85 | 2.30 | 85 | 1.53 | 185 | 3.33 | |
| 90 | 2.43 | 90 | 1.62 | 190 | 3.42 | |
| 95 | 2.57 | 95 | 1.71 | 195 | 3.51 | |
| 100 | 2.70 | 100 | 1.80 | 200 | 3.60 |
355.120 Marking. Each length of RTRC 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 inclu‐ ded 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 mate‐ rial.
Informational Note: Examples of these markings include but are not limited to “limited smoke” and “sunlight resistant.”