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