Article 392 Cable Trays

392.1

Scope

392.2

Definition

392.3

Uses Permitted

Cable tray can be used as a support system for branch circuits, service conductors, feeders, services, communication circuits, control circuits, and signaling circuits. It is not limited to industrial locations. If it is exposed to direct sunlight then jacketed cables or insulated conductors that are sunlight resistant must be used.

(A) Wiring Methods. Refer to the noted article or section for the conditions of use of the following:

 

Article

Section

Armored cable

333

 

Communication raceways

800

 

Electrical metallic tubing

358

 

Electrical nonmetallic tubing

362

 

Fire alarm cables

760

 

Flexible metal conduit

348

 

Flexible metallic tubing

360

 

Instrumentation tray cable

727

 

Intermediate metal conduit

342

 

Liquidtight flexible metal conduit

350

 

Liquidtight flexible nonmetallic conduit

356

 

Metal-clad cable

330

 

Mineral-insulated, metal-sheathed cable

332

 

Multiconductor service-entrance cable

338

 

Multiconductor underground feeder and branch-circuit cable

340

 

Multipurpose and communications cables

800

 

Nonmetallic-sheathed cable

334

 

Power and control cable

336

 

Power-limited tray cable

 

725.61(C) and 725.71(F)

Optical fiber cables

770

 

Optical fiber racways

770

 

Other factory-assembled, multiconductor control, signal, or power cables that are specifically approved for installation in cable trays

   

Rigid metal conduit

344

 

Rigid nonmetallic conduit

352

 

(B) In Industrial Establishments. Wiring methods of 392.3(A) can be used in accordance with their respective article's requirements. Where only qualified maintenance personnel are available, certain cables are permitted in ladder, ventilated trough, and ventilated channel-type cable trays. Single-conductor cable must be 1/0 AWG or larger and be permitted to be used in cable tray. If the cable is sized 1/0 AWG through 4/0 AWG, it must be installed in ladder-type cable tray with a maximum rung spacing of 9 in. or in ventilated trough cable tray. Welding cable can be installed in accordance with Article 630, Part IV. Equipment grounding single conductors can be insulated, covered, or bare 4 AWG or larger. Multiconductor cable type MV can also be installed as noted above.

(C) Equipment Grounding Conductors

(D) Hazardous (Classified) Locations

(E) Nonmetallic Cable Tray

392.4

Uses Not Permitted

Cable trays cannot be used where they are exposed to severe physical injury, in hoistways, and in environmental air-handling spaces. An exception is made in the latter case where used to support a wiring method noted in Section 300.22.

392.5

Construction Specifications

Cable trays must have proper strength and rigidity, smooth edges, be protected against corrosion, have side rails, and contain the proper fittings. Flame-retardant material must be used for nonmetallic cable tray.

392.6

Installation

The cable tray system must be installed completely as a system before the cables are installed, have the proper supports, and have covers where required. Multiconductor cables can be installed in the same tray if 600 V or less. Cables over 600 V cannot be installed with cables under 600 V, with two exceptions. The cable trays must be exposed and accessible and have room around them for adequate access. They can go through partitions, walls, and floors if installed in accordance with Section 300.21 (proper and approved firestopping methods used). Incidental support from cable tray is permitted where approved and designed to support the load. Additional requirements are noted.

392.7

Grounding

Proper grounding must be attained in compliance with Article 250.96. The entire system must be grounded. Minimum size steel and aluminum trays are indicated in Table 392.7(B) of the NEC®.

392.8

Cable Installation

  1. Splices are permitted if approved methods are used, they are accessible, and are not over the side rails.
  2. Cables must be fastened in sloping or vertical runs.
  3. If the cable is installed in a bushed conduit and tubing for protection or support, a box is not required.
  4. If installed in parallel, the conductors must be grouped with one conductor per phase in each group. Single conductors must be bound in circuit groups.
  5. Single conductors.

392.9

Number of Multiconductor Cables, Rated 2000 Volts, Nominal, or Less, in Cable Trays

Refer to this section in the Code and Table 392.9.

392.10

Number of Single Conductor Cables, Rated 2000 Volts or Less, in Cable Trays

Refer to this section in the Code and Table 392.10(A).

392.11

Ampacity of Cables Rated 2000 Volts or Less in Cable Trays

(A) Multiconductor Cables. Multiconductor cables, rated 2000 V or less, installed as per Section 392.9 are to follow ampacities in Tables 310.16 and 310.18. The derating factors of Section 310.15(B)(2)(a) apply only to multiconductor cables of three or more current carrying conductors in cable, not in cable tray. If the tray is covered for more than 6 ft. with a solid unventilated cover, the ampacities allowed are 95% of those shown in the tables. An additional exception is allowed for a single layer in uncovered trays.

Table 310.18. Allowable Ampacities of Insulated Conductors Rated 0 through 2000 Volts, 150° through 250°C (302°F through 482°F), Not More than Three Current-Carrying Conductors in Raceway or Cable Based on Ambient Air Temperature of 40°C (104°F)

Size AWG or kcmil

Temperature Rating of Conductor (See Table 310.13)

Size AWG or kcmil

150°C (302°F)

200°C (392°F)

250°C (482°F)

150°C (302°F)

Type Z

Types FEP, FEPB, PFA, SA

Types PFAH, TFE

Type Z

Copper

Nickel or Nickel-Coated Copper

Aluminum or Copper-Clad Aluminum

14

34

36

39

. . . .

14

12

43

45

54

30

12

10

55

60

73

44

10

8

76

83

93

57

8

6

96

110

117

75

6

4

120

125

148

94

4

3

143

152

166

109

3

2

160

171

191

124

2

1

186

197

215

145

1

1/0

215

229

244

169

1/0

2/0

251

260

273

198

2/0

3/0

288

297

308

227

3/0

4/0

332

346

361

260

4/0

Correction Factors

Ambient Temp. (°C)

For ambient temperatures other than 40°C (104°F), multiply the allowable ampacities shown above by the appropriate factor shown below

Ambient Temp. (°F)

41-50

0.95

0.97

0.98

0.95

105-122

51-60

0.90

0.94

0.95

0.90

123-140

61-70

0.85

0.90

0.93

0.85

141-158

71-80

0.80

0.87

0.90

0.80

159-176

81-90

0.74

0.83

0.87

0.74

177-194

91-100

0.67

0.79

0.85

0.67

195-212

101-120

0.52

0.71

0.79

0.52

213-248

121-140

0.30

0.61

0.72

0.30

249-284

141-160

. . . .

0.50

0.65

. . . .

285-320

161-180

. . . .

0.35

0.58

. . . .

321-356

181-200

. . . .

. . . .

0.49

. . . .

357-392

201-225

. . . .

. . . .

0.35

. . . .

393-437

(B) Single Conductor Cables. The derating factors of Section 310.15(B)(2)(a) don't apply to cables in cable tray. Single conductor or single conductors cabled together, rated 2000 V or less, properly installed in accordance with the Code, are to use ampacities as follows:

(1) Cables 600 kcmil and larger in uncovered trays use not more than 75% of the ampacities in Tables 310.17 and 310.19. If the tray is covered for more than 6 ft. with unventilated covers, use a maximum 70% of the ampacities in the tables.

Table 310.17. Allowable Ampacities of Single-Insulated Conductors Rated 0 through 2000 Volts in Free Air Based on Ambient Temperature of 30°C (86°F)

Size AWG or kcmil

Temperature Rating of Conductor (See Table 310.13)

Size AWG or kcmil

60°C (140°F)

75°C (167°F)

90°C (194°F)

60°C (140°F)

75°C (167°F)

90 °C (194°F)

Types TW, UF

Types RHW, THHW, THW, THWN, XHHW, ZW

Types TBS, SA, SIS, FEP, FEPB, MI, RHH, RHW-2, THHN, THHW, THW-2, THWN-2 USE-2, XHH, XHHW, XHHW-2, ZW-2

Types TW, UF

Types RHW, THHW, THW, THWN, XHHW

Types TBS, SA, SIS, THHN, THHW, THW-2, THWN-2, RHH, RHW-2, USE-2, XHH, XHHW, XHHW-2, ZW-2

Copper

Aluminum or Copper-Clad Aluminum

18

. . . .

. . . .

18

. . . .

. . . .

. . . .

. . . .

16

. . . .

. . . .

24

. . . .

. . . .

. . . .

. . . .

14[*]

25

30

35

. . . .

. . . .

. . . .

. . . .

12[*]

30

35

40

25

30

35

12[*]

10[*]

40

50

55

35

40

40

10[*]

8

60

70

80

45

55

60

8

6

80

95

105

60

75

80

6

4

105

125

140

80

100

110

4

3

120

145

165

95

115

130

3

2

140

170

190

110

135

150

2

1

165

195

220

130

155

175

1

1/0

195

230

260

150

180

205

1/0

2/0

225

265

300

175

210

235

2/0

3/0

260

310

350

200

240

275

3/0

4/0

300

360

405

235

280

315

4/0

250

340

405

455

265

315

355

250

300

375

445

505

290

350

395

300

350

420

505

570

330

395

445

350

400

455

545

615

355

425

480

400

500

515

620

700

405

485

545

500

600

575

690

780

455

540

615

600

700

630

755

855

500

595

675

700

750

655

785

885

515

620

700

750

800

680

815

920

535

645

725

800

900

730

870

985

580

700

785

900

1000

780

935

1055

625

750

845

1000

1250

890

1065

1200

710

855

960

1250

1500

980

1175

1325

795

950

1075

1500

1750

1070

1280

1445

875

1050

1185

1750

2000

1155

1385

1560

960

1150

1335

2000

Correction Factors

Ambient Temp. °C

For ambient temperatures other than 30°C (86°F), multiply the allowable ampacities shown above by the appropriate factor shown below.

Ambient Temp. °F

21-25

1.08

1.05

1.04

1.08

1.05

1.04

70-77

26-30

1.00

1.00

1.00

1.00

1.00

1.00

79-86

31-35

0.91

0.94

0.96

0.91

0.94

0.96

87-95

36-40

0.82

0.88

0.91

0.82

0.88

0.91

96-104

41-45

0.71

0.82

0.87

0.71

0.82

0.87

105-113

46-50

0.58

0.75

0.82

0.58

0.75

0.82

114-122

51-55

0.41

0.67

0.76

0.41

0.67

0.76

123-131

56-60

. . . .

0.58

0.71

. . . .

0.58

0.71

132-140

61-70

. . . .

0.33

0.58

. . . .

0.33

0.58

141-158

71-80

. . . .

. . . .

0.41

. . . .

. . . .

0.41

159-176

For table headings see page 98.

 

[*] See Section 240.4(D).

Table 310.19. Allowable Ampacities of Single-Insulated Conductors Rated 0 through 2000 Volts, 150°C through 250°C (302° through 482°F), in Free Air Based on Ambient Air Temperature of 40°C (104°F)

Size AWG or kcmil

Temperature Rating of Conductor, See Table 310.13

Size AWG or kcmil

150°C (302°F)

200°C (392°F)

250°C (482°F)

150°C (302°F)

Type Z

Types FEP, FEPB, PFA, SA

Types PFAH, TFE

Type Z

Copper

Nickel or Nickel-Coated Copper

Aluminum or Copper-Clad Aluminum

14

46

54

59

. . . .

14

12

60

68

78

47

12

10

80

90

107

63

10

8

106

124

142

83

8

6

155

165

205

112

6

4

190

220

278

148

4

3

214

252

327

170

3

2

255

293

381

198

2

1

293

344

440

228

1

1/0

339

399

532

263

1/0

2/0

390

467

591

305

2/0

3/0

451

546

708

351

3/0

4/0

529

629

830

411

4/0

Correction Factors

Ambient Temp (°c)

For ambient temperatures other than 40°C (104°F), multiply the allowable ampacities shown above by the appropriate factor shown below

Ambient Temp. (°F)

41-50

0.95

0.97

0.98

0.95

105-122

51-60

0.90

0.94

0.95

0.90

123-140

61-70

0.85

0.90

0.93

0.85

141-158

71-80

0.80

0.87

0.90

0.80

159-176

81-90

0.74

0.83

0.87

0.74

177-194

91-100

0.67

0.79

0.85

0.67

195-212

101-120

0.52

0.71

0.79

0.52

213-248

121-140

0.30

0.61

0.72

0.30

249-284

141-160

. . . .

0.50

0.65

. . . .

285-320

161-180

. . . .

0.35

0.58

. . . .

321-356

181-200

. . . .

. . . .

0.49

. . . .

357-392

201-225

. . . .

. . . .

0.35

. . . .

393-437

 

(2) Cables 1/0 AWG through 500 kcmil in uncovered trays use not more than 65% of the ampacities in Tables 310.17 and 310.19. If the tray is covered for more than 6 ft. with unventilated covers, use a maximum 60% of the ampacities in the tables.

(3) If single conductor cables are placed in a single layer with at least one cable diameter separation, the tray is uncovered and the cable is 1/0 AWG or larger, the ampacities in Tables 310.17 and 310.19 may be used. There is one exception.

(4) Special allowance when installed in uncovered tray with a triangular configuration.

392.12

Number of Type MV and Type MC Cables (2001 Volts or Over) in Cable Trays

392.13

Ampacity of Type MV and Type MC Cables (2001 Volts or Over) in Cable Trays






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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