Article 352 Rigid Nonmetallic Conduit Type RNC

I. General

352.1

Scope

352.2

Definition

A conduit which is circular in cross section and made from a nonmetallic material.

352.6

Listing Requirements

The RNC, elbows, and associated fittings must be listed.

II. Installation

352.10

Uses Permitted

Some of the uses permitted and other references in the NEC® are: concealed in walls, floors, ceilings, and cinder fill; exposed when not subject to injury; in corrosive locations where approved for that type of location and in accordance with Section 300.6; in dry and damp locations in accordance with Section 352.12; in wet locations where the entire system is installed to prevent water from getting into the conduit and all bolts, screws, and so forth are corrosion resistant and underground in accordance with Sections 300.5 and 300.50. There is a provision for use as a support in certain specific cases.

352.12

Uses Not Permitted

This type of conduit must not be used in hazardous locations except where permitted by Sections 503.10(A), 504.20, 514.8 exception 2, 515.8, and the Class 1, Division 2 locations in Section 501.10(B)(3); in areas where there might be physical damage to the conduit; in theaters and similar locations except as noted in Articles 518 and 520; where the temperature rating of the conduit is exceeded by that of the conductor insulation; in areas where the ambient temperature exceeds 50°C (122°F) unless otherwise listed; and for supporting fixtures or other equipment not described in 352.10(H).

352.20

Size

The minimum size is metric designator 16 (trade size ½). The maximum size is metric designator 155 (trade size 6).

352.22

Number of Conductors

Cannot exceed the percentage fill of Table 1, Chapter 9. Cables can be used if not prohibited by cable articles. Cable cannot exceed the fill requirements of Table 1, Chapter 9.

352.24

BendsHow Made

The conduit must not be injured. Refer to Table 2, Chapter 9.

352.26

BendsNumber in One Run

The maximum that is permitted is not more than 360° in bends between pull points.

352.28

Trimming

Remove rough edges on cuts.

352.30

Securing and Supporting

Refer to Section 300.18 and Table 352.30(B) for spacing of supports. It must be fastened no farther than 900 mm (3 ft.) from a termination point. If it is listed for other securing spacing, it is permitted to follow but not exceed the listing. There is an exception for supports by openings through framing members of horizontal runs.

352.44

Expansion Fittings

Expansion fittings have to be provided to compensate for thermal expansion and contraction where the change in length according to Table 352.44(A) or (B) will be 6 mm (¼ in.) or greater between securely mounted conduit terminations.

Table 352.44(A). Expansion Characteristics of PVC Rigid Nonmetallic Conduit Coefficient of Thermal Expansion = 6.084 x 105 mm/mm/°C (3.38 x 105 in./in./°F)

Temperature Change (°C)

Length Change of PVC Conduit (mm/m)

Temperature Change (°F)

Length Change of PVC Conduit (in./100 ft.)

Temperature Change (°F)

Length Change of PVC Conduit (in./100 ft.)

5

0.30

5

0.20

105

4.26

10

0.61

10

0.41

110

4.46

15

0.91

15

0.61

115

4.66

20

1.22

20

0.81

120

4.87

25

1.52

25

1.01

125

5.07

30

1.83

30

1.22

130

5.27

35

2.13

35

1.42

135

5.48

40

2.43

40

1.62

140

5.68

45

2.74

45

1.83

145

5.88

50

3.04

50

2.03

150

6.08

55

3.35

55

2.23

155

6.29

60

3.65

60

2.43

160

6.49

65

3.95

65

2.64

165

6.69

70

4.26

70

2.84

170

6.90

75

4.56

75

3.04

175

7.10

80

4.87

80

3.24

180

7.30

85

5.17

85

3.45

185

7.50

90

5.48

90

3.65

190

7.71

95

5.78

95

3.85

195

7.91

100

6.08

100

4.06

200

8.11

Table 352.44(B). Expansion Characteristics of Reinforced Thermosetting Resin Conduit (RTRC) Coefficient of Thermal Expansion = 2.7 x 105 mm/mm/°C (1.5 x 105 in./in./°F)

Temperature Change (°C)

Length Change of PVC Conduit (mm/m)

Temperature Change (°F)

Length Change of PVC Conduit (in./100 ft.)

Temperature Change (°F)

Length Change of PVC 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

352.46

Bushings

A bushing must be used at the point where the conduit goes into a box or fitting unless protection is provided in the box or fitting.

352.48

Joints

Use approved methods.

352.56

Splices and Taps

They are permitted only in accordance with Section 300.15.

352.60

Grounding

A separate equipment grounding conductor must be installed where equipment grounding is required. There are two exceptions.

III. Construction Specifications

352.100

Construction

RNC and fittings must be composed of a nonmetallic material. It must be resistant to moisture and chemical atmospheres. Above ground it must be flame resistant, resistant to impact and crushing, resistant to distortion from heat, and resistant to low temperature and sunlight. Below ground it must be resistant to corrosive agents and moisture, be able to withstand crushing and other abuse. If it is direct buried without encasement in concrete, it must be able to resist the continued loading it will encounter.

352.120

Marking

It must be marked at least every 3 m (10 ft.) in each length. There are requirements for marking on conduit used above and below ground.





Pocket Guide to the National Electrical Code 2005
Pocket Guide to the National Electrical Code(R), 2005 Edition (8th Edition)
ISBN: 0131480014
EAN: 2147483647
Year: 2004
Pages: 120
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