SO Cable Selection Guide

SO Cable Selection Guide SO cable is a type of flexible multi-conductor cable (or portable cord) rated for 600V "extra hard usage" and made with an oil resistant outer jacket. As a multi-conductor, SO cable comes with two or more individually insulated conductors all bound tightly together by an outer insulation jacket. SO cable ranges in size from 18 AWG to 2 AWG. SO cable has been largely replaced by SOOW cable, which provides better protection against oil and moisture. Similarly, SJ cable rated for 300V "junior hard service" has been replaced by SJOW. The National Electrical Code (NEC) uses various letters to provide information about the insulation, including temperature ratings, construction material, and intended uses. The extra hard usage rating applies if the S is by itself (no J, P, or V afterwards), which means the cable is rated for 600V and designed to withstand physical damage such as cuts, impacts, and abrasions. Please refer to our article on cable types for more information about letter designations.

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Fixed vs. Flexible Cables

Two general groups of conductor cables are used in the U.S.

Fixed Cable

Used in non-moving installations where the cables are fixed in place.

Flexible Cable (or Portable Cord)

Used in applications where flexible cables with a higher tensile strength are needed or preferred (e.g. pendant cables). Another common name for flexible cables is portable cords, because portable machines, like welders or stage lighting equipment, often require flexible wiring.

Is fixed cable only used for permanent wiring and flexible cable only for temporary, non-permanent wiring? It is more accurate to say that flexible cable is used for portable power supply because "portable" implies the cable will be moved around and, thus, need to be flexible.

A common misconception is that fixed cables are only used for permanent wiring (i.e. long-term) applications and that flexible or portable cables are only used for temporary wiring applications. In fact, fixed and flexible cables can be used for either permanent or temporary wiring applications. There are plenty of applications where you need flexible cables for permanent, long-term power supply. The key difference is whether your cables will be fastened in place or if they need to be flexible (i.e. can bend, stretch, rolled into coils, etc.).

Note for Electric Welders: Flexible cables designed specifically for use with electric welders are called welding cables. Resistance and arc welders are considered “Special Equipment” and covered in chapter 6 of the NEC. In particular, article 630 gives additional requirements when sizing welding cable for resistance and arc welders. We encourage you to look over article 630 for yourself since it’s only about two and a half pages in the 2011 edition.

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How to Select SO Cable

The content we provide is meant to inform you and help support the proper selection and use of conductor cables. As always, we recommend consulting a licensed and competent electrician to help you with the sizing and selection of parts for your particular application.

The Weakest Link » Ampacity » Number of Conductors »

Terminal Temperature Ratings » Cable Size and Length » Insulation »

Insulation Temperature Rating » Ambient Temperature »

Strand Count » Conductor Stranding Classes »

The primary issue with electrical circuits is that any electrical current produces some amount of heat due to resistance, and circuit components need to be selected so that they can both supply the necessary power to equipment and handle the heat generated by the current being drawn. Thus, you need to consider:

1) The heat generated by the conductor.
2) The heat generated at the terminal connections to equipment.
3) The heat from the ambient temperature.

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NEC U.S. Standards for Conductor Sizing

For more information on the proper conductor sizing please refer to the latest edition (updated every 3 years) of the NEC, available for free online viewing at nfpa.org. Understanding chapters 1-4 in particular will help with sizing conductors for general wiring.

For conductors rated between 0-2000 volts, knowing article 110.14 (C) and 310.15 in the 2011 NEC is crucial, so we recommend consulting the most recent edition of the NEC for yourself in addition to consulting a licensed electrician.

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The Weakest Link

According to article 110.14 (C), conductors must be selected based on the "lowest temperature rating of any connected termination, conductor, or device." Article 310.15 (A) explains all about the limiting temperature and ampacity ratings for a conductor, and the tables in 310.15 (B) list allowable conductor ampacities.

The reason you need multiple tables is because each table deals with different "conditions of use," which is simply an NEC term that refers to factors that will affect conductor ampacity, such as terminal temperature ratings and ambient temperature. Thus, you can have different ampacities along the length of the same cable depending on the conditions of use.

The NEC also recognizes that for certain applications (i.e. conditions of use) there may be different ampacities for the same cable. Article 310.15(A)(2) states that if a given conductor has more than one ampacity, then the lower ampacity rating must be used for the entire length when sizing the conductor. For example, if you want to use 10 AWG cable but notice that part of the cable will be exposed to direct sunlight (e.g. on a rooftop), then you will need to adjust the ampacity rating of the entire length of 10 AWG cable for the part exposed to sunlight. As a result, you may need to use 8 AWG or higher.

As a general rule, size your wires according to your lowest (limiting) ampacity calculation for conductors, and the lowest (limiting) temperature rating for terminal connections.

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Ampacity

This is the most important factor in selecting any conductor cable. The NEC defines ampacity as, "The current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating" (Article 100 "Definitions").

Ampacity, short for amperage capacity, refers to the maximum current a conductor can carry without damaging the insulation or any other connected terminals. The "temperature rating" refers to the maximum allowable insulation temperature rating. The more current you have running through a conductor, the more heat will be generated due to electrical resistance.

Allowable Ampacities for Types of Flexible Cables - Table 400.5 (A)(1)

Based on a 30°C (86°F) ambient temperature. 2011 NEC

Size (AWG)	Thermoplastic Types TPT, TST	Thermoset Types C, E, EO, PD, S, SJ, SJO, SJOW, SJOO, SJOOW, SO, SOW, SOO, SOOW, SP-1, SP-2, SP-3, SRD, SV, SVO, SVOO		Types HPD, HPD, HSJ, HSJO, HSJOO
		Thermoplastic Types ET, ETLB, ETP, ETT, SE, SEW, SEO, SEOW, SEOOW, SJE, SJEW, SJEO, SJEOW, SJEOOW, SJT, SJTW, SJTO, SJTOW, SJTOO, SJTOOW, SPE-1, SPE-2, SPE-3, SPT-1, SPT-1W, SPT-2, SPT-2W, SPT-3, ST, SRDE, SRDT, STO, STOW, STOO, STOOW, SVE, SVEO, SVT, SVTWO, SVTOO
		Column A	Column B
27*	0.5	-	-	-
20	-	5**	***	-
18	-	7	10	10
17	-	9	12	13
16	-	10	13	15
15	-	12	16	17
14	-	15	18	20
12	-	20	25	30
10	-	25	30	35
8	-	35	40	-
6	-	45	55	-
4	-	60	70	-
2	-	80	95	-

*0.5 amps for tinsel cord. This type of cable is used where flexibility is the chief concern for a conductor.

**For elevator cables only.

***7 amps for elevator cables; 2 amps for everything else.

Column A lists ampacities for multi-conductors used in connections such that only 3 conductors are carrying current. Column B lists ampacities for multi-conductors used in connections so that only 2 conductors are carrying current.

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Number of Conductors

 

The more current-carrying conductors you have bundled together in one jacket, the more you will have to derate (reduce) the SO cable's ampacity.

Number of Conductors	% of Value in Tables 400.5(A) and 400.5(B)
4 - 6	80
7 - 9	70
10 - 20	50
21 - 30	45
31 - 40	40
41 and above	35

Terminal Temperature Ratings

100 Amps or Less

Article 110.14 (C)(1) states that for equipment rated 100 amps or less, "unless the equipment is listed and marked otherwise, conductor ampacities used in determining equipment [terminals] shall be based on [the 60°C column]."

For example, you want to run a 35 amp piece of equipment and are looking at copper conductors. Since there is no marking to indicate otherwise, and 35 is less than 100, then you should assume your equipment terminals are rated for 60°C and choose your wire gauge based on the 60°C column for copper conductors in table 310.15 (B)(16) from the 2011 NEC.

More than 100 Amps

Unless otherwise indicated, for equipment rated more than 100 amps, assume that the terminals are rated for 75°C, and use the 75°C column.

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Cable Size (Gauge) and Length

Ampacity ratings decrease as the cable gets longer and thinner. In other words, long thin cables have higher electrical resistance than shorter and thicker cables.

Gauge

Smaller gauge ratings actually refer to thicker cables. The smallest gauge (thickest cable) is 0000 or 4/0, pronounced "four aught," and thicker cables have their cross-sectional areas directly listed in kcmils. (A mil is 1/1000 inch, a cmil is the area of a circle with a diameter of 1 mil. 1 kcmil is simply 1000 cmils).

Length

This should be self-explanatory. Your SO cable must be long enough for your application. However, keep in mind that longer cables increase resistance and decrease ampacity, so you may need to buy thicker cable (smaller gauge ratings) to offset the increased resistance.

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Insulation

Insulation serves several functions. Primarily, insulation prevents conductors from short-circuiting, protects conductors from the application environment (e.g. moisture, dust, oil, chemicals, physical damage, etc.), and protects people from electrical shock. Insulation material will also affect how flexible a cable is.

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Insulation Temperature Rating

Ampacity also depends on the insulation temperature rating. This rating refers to the ambient temperature beyond which (or below if a minimum temperature rating is provided) the insulation will be damaged by operating current of the conductor.

Temperature Rating of Conductor - Table 310.15(B)(16) (2011 NEC) - raceway, multi-conductor cable, or Direct-Buried

Allowable ampacities of insulated conductors rated 60°C to 90°C (140°F to 194°F), 0 to 2000 Volts with no more than 3 current-carrying conductors in a raceway, multi-conductor cable, or earth (Directly Buried), based on a 30°C (86°F) ambient temperature. See table 400.5 (A) for ampacity adjustment factors for more than 3 conductors in a cable.

The title "Temperature Rating of Conductor" is misleading. The temperatures at the top of the table and the letter types directly below actually refer to the insulation type. The amp ratings for copper (and aluminum) refer to how many amps the conductor can carry before damaging the insulation rated for either 60°C, 75°C, or 90°C. For example, an 18 AWG copper conductor with THHN insulation (rated for 90°C can carry up to 14 amps if the ambient temperature is 30°C or less.

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
		Copper			Aluminum or Copper-clad Aluminum
		TW, UF	RHW, THHW, THW, THWN, XHHW, USE, ZW	TBS, SA, SIS, FEP, FEPB, MI, RHH, RHW-2, THHN, THHW, THW-2, THWN-2, USE-2, XHH, XHHW, XHHW-2, ZW-2	TW, UF	RHW, THHW, THW, THWN, XHHW, USE	TBS, SA, SIS, THHN, THHW, THW-2, THWN-2, RHH, RHW-2, USE-2, XHH, XHHW, XHHW-2, ZW-2
18		-	-	14	-	-	-
16		-	-	18	-	-	-
14*		15	20	25	-	-	-
12*		20	25	30	15	20	25
10*		30	35	40	25	30	35
8		40	50	55	30	40	45
6		55	65	75	40	50	55
4		70	85	95	55	65	75
3		85	100	115	65	75	85
2		95	115	130	75	90	100
1		110	130	145	85	100	115
1/0		125	150	170	100	120	135
2/0		145	175	195	115	135	150
3/0		165	200	225	130	155	175
4/0		195	230	260	150	180	205
250		215	255	290	170	205	230
300		240	285	320	195	230	260
350		260	310	350	210	250	280
400		280	335	380	225	270	305
500		320	380	430	260	310	350
600		350	420	475	285	340	385
700		385	460	520	315	375	420
750		400	475	535	320	385	435
800		410	490	555	330	395	445
900		435	520	585	355	425	480
1000		455	545	615	375	445	500
1250		495	590	665	405	485	545
1500		520	625	705	435	520	585
1750		545	650	735	455	545	615
2000		555	665	750	470	560	630

Table 310.15(B)(17) (2011 NEC) - open air

Allowable ampacities of insulated conductors rated 60°C to 90°C (140°F to 194°F), 0 to 2000 Volts for conductors with only a single insulation layer based on a 30°C (86°F) ambient temperature.

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
		Copper			Aluminum or Copper-clad Aluminum
		TW, UF	RHW, THHW, THW, THWN, XHHW, USE, ZW	TBS, SA, SIS, FEP, FEPB, MI, RHH, RHW-2, THHN, THHW, THW-2, THWN-2, USE-2, XHH, XHHW, XHHW-2, ZW-2	TW, UF	RHW, THHW, THW, THWN, XHHW, USE	TBS, SA, SIS, THHN, THHW, THW-2, THWN-2, RHH, RHW-2, USE-2, XHH, XHHW, XHHW-2, ZW-2
18		-	-	18	-	-	-
16		-	-	24	-	-	-
14*		25	30	35	-	-	-
12*		30	35	40	25	30	35
10*		40	50	55	35	40	45
8		60	70	80	45	55	60
6		80	95	105	60	75	85
4		105	125	140	80	100	115
3		120	145	165	95	115	130
2		140	170	190	110	135	150
1		165	195	220	130	155	175
1/0		195	230	260	150	180	205
2/0		225	265	300	175	210	235
3/0		260	310	350	200	240	270
4/0		300	360	405	235	280	315
250		340	405	455	265	315	355
300		375	445	500	290	350	395
350		420	505	570	330	395	445
400		455	545	615	355	425	480
500		515	620	700	405	485	545
600		575	690	780	455	545	615
700		630	755	850	500	595	670
750		655	785	885	515	620	700
800		680	815	920	535	645	725
900		730	870	980	580	700	790
1000		780	935	1055	625	750	845
1250		890	1065	1200	710	855	965
1500		980	1175	1325	795	950	1070
1750		1070	1280	1445	875	1050	1185
2000		1155	1385	1560	960	1150	1295

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Ambient Temperature

The temperature of the surrounding environment affects a conductor's ability to dissipate heat. Higher ambient temperatures will reduce your SO cable's ampacity.

NEC table 310.15(B)(2)(a)

Ampacity correction factors for ambient temperatures other than 30°C. Just multiply the ampacities in a given table by the number given in table 310.15(B)(2)(a). Make sure to use the correction factor under the right insulation temperature rating--either 60°C, 75°C, or 90°C.

CORRECTION FACTORS based on 30°C (86°F) ambient temperature
Ambient Temperature		Insulation temperature rating
°C	°F	60°C	75°C	90°C
10 or less	50 or less	1.29	1.20	1.15
11 - 15	51 - 59	1.08	1.05	1.04
16 - 20	60 - 68	1.08	1.05	1.04
21 - 25	69 - 77	1.08	1.05	1.04
26 - 30	78 - 86	1.00	1.00	1.00
31 - 35	87 - 95	0.91	0.94	0.96
36 - 40	96 - 104	0.82	0.88	0.91
41 - 45	105 - 113	0.71	0.82	0.87
46 - 50	114 - 122	0.58	0.75	0.82
51 - 55	123 - 131	0.71	0.67	0.76
56 - 60	132 - 140	-	0.58	0.71
61 - 70	141 - 158	-	0.33	0.58
71 - 80	159 - 176	-	-	0.41

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Strand Count

Cables with higher strand counts are more flexible.

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Conductor Stranding Classes

The American Society for Testing and Materials (ASTM), is an internationally recognized organization that sets the standards for conductor stranding, and both the NEC and UL follow ASTM standards for conductor stranding. Conductors with higher strand classes (e.g. D, G, or H) require specifically identified connectors for the higher strand classes. A table detailing conductor stranding classes B and C is shown below, and for more information on selecting connectors see SOOW wire connectors.

Conductor Size		Number of Strands
		Copper		Aluminum
AWG or kcmil	mm2	Class B	Class C	Class B
24 - 30	0.20 - 0.05	a	-	-
22	0.32	7	-	-
20	0.52	10	-	-
18	0.82	16	-	-
16	1.3	26	-	-
14 - 2	2.1 - 33.6	7	19	7b
1 - 4/0	42.4 - 107	19	37	19
250 - 500	127 - 253	37	61	37
600 - 1000	304 - 508	61	91	61
1250 - 1500	635 - 759	91	127	91
1750 - 2000	886 - 1016	127	271	127
aStrand counts vary. bAluminum 14 AWG (2.1 mm2) is not available.

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Product Selection

View our full selection of SOOW cable below. Click on a part number to view detailed information on the product page.

2/3

Feet per pound: 0.84
Amps per conductor: 95
Conductor stranding: 133 strands each
Insulation thickness: 0.05 in.
Nominal outside diameter: 1.08 in.

Length (ft.)	Weight (lbs.)	TEMCo ID
5	5.95	SOO388
10	11.9	SOO389
15	17.85	SOO390
20	23.8	SOO391
25	29.75	SOO392
30	35.7	SOO393
35	41.65	SOO394
40	47.6	SOO395
50	59.5	SOO396
65	77.35	SOO397
75	89.25	SOO398
85	101.15	SOO399
100	119	SOO400
125	148.75	SOO401
150	178.5	SOO402
175	208.25	SOO403
200	238	SOO404
225	267.5	SOO405
250	297.5	SOO406
300	357	SOO407
400	476	SOO408
500	595	SOO409
1000	1190	SOO410

2/4

Feet per pound: 0.68
Amps per conductor: 80
Conductor stranding: 133 strands each
Insulation thickness: 0.05 in.
Nominal outside diameter: 1.17 in.

Length (ft.)	Weight (lbs.)	TEMCo ID
5	7.38	SOO411
10	14.75	SOO412
15	22.13	SOO413
20	29.5	SOO414
25	36.88	SOO415
30	44.25	SOO416
35	51.63	SOO417
40	59	SOO418
50	73.75	SOO419
65	95.88	SOO420
75	110.63	SOO421
85	125.38	SOO422
100	147.5	SOO423
125	184.38	SOO424
150	221.25	SOO425

4/4

Feet per pound: 0.71
Amps per conductor: 60
Conductor stranding: 133 strands each
Insulation thickness: 0.05 in.
Nominal outside diameter: 1.01 in.

Length (ft.)	Weight (lbs.)	TEMCo ID
5	7.03	SOO342
10	14.05	SOO343
15	21.08	SOO344
20	28.1	SOO345
25	35.13	SOO346
30	42.15	SOO347
35	49.18	SOO348
40	56.2	SOO349
50	70.25	SOO350
65	91.33	SOO351
75	105.38	SOO352
85	119.43	SOO353
100	140.5	SOO354
125	175.63	SOO355
150	210.75	SOO356
175	245.88	SOO357
200	281	SOO358
225	316.13	SOO359
250	351.25	SOO360
300	421.5	SOO361
400	562	SOO362
500	702.5	SOO363
1000	1405	SOO364

4/5

Feet per pound: 0.69
Amps per conductor: 48
Conductor stranding: 133 strands each
Insulation thickness: 0.05 in.
Nominal outside diameter: 1.11 in.

Length (ft.)	Weight (lbs.)	TEMCo ID
5	7.25	SOO365
10	14.5	SOO366
15	21.75	SOO367
20	29	SOO368
25	36.25	SOO369
30	43.5	SOO370
35	50.75	SOO371
40	58	SOO372
50	72.5	SOO373
65	94.25	SOO374
75	108.75	SOO375
85	123.25	SOO376
100	145	SOO377
125	181.25	SOO378
150	217.5	SOO379
175	253.75	SOO380
200	290	SOO381
225	326.25	SOO382
250	362.5	SOO383
300	435	SOO384
400	580	SOO385
500	725	SOO386
1000	1450	SOO387

6/3

Feet per pound: 1.78
Amps per conductor: 45
Conductor stranding: 133 strands each
Insulation thickness: 0.05 in.
Nominal outside diameter: 0.79 in.

Length (ft.)	Weight (lbs.)	TEMCo ID
5	2.81	SOO021
10	.62	SOO022
15	8.43	SOO023
20	11.24	SOO024
25	14.05	SOO025
30	16.86	SOO026
35	19.67	SOO027
40	22.48	SOO028
50	28.11	SOO029
65	36.54	SOO030
75	42.16	SOO031
85	47.78	SOO032
100	56.21	SOO033
125	70.26	SOO034
150	84.32	SOO035
175	98.37	SOO036
200	112.42	SOO037
225	126.48	SOO038
250	140.53	SOO039
300	168.63	SOO040
400	224.85	SOO041
500	281.06	SOO042

6/4

Feet per pound: 1.51
Amps per conductor: 36
Conductor stranding: 133 strands each
Insulation thickness: 0.05 in.
Nominal outside diameter: 0.86 in.

Length (ft.)	Weight (lbs.)	TEMCo ID
5	3.3	SOO000
10	6.6	SOO001
15	9.9	SOO002
20	13.2	SOO003
25	16.5	SOO004
30	19.8	SOO005
35	23.1	SOO006
40	26.4	SOO007
50	33	SOO008
65	42.9	SOO009
75	49.5	SOO010
85	56.11	SOO011
100	66.01	SOO012
125	82.51	SOO013
150	99.01	SOO014
175	115.51	SOO015
200	132.01	SOO016
225	148.51	SOO017
250	165.02	SOO018
300	198.02	SOO019
400	264.03	SOO020

6/5

Feet per pound: 1.24
Amps per conductor: 36
Conductor stranding: 133 strands each
Insulation thickness: 0.05 in.
Nominal outside diameter: 0.95 in.

Length (ft.)	Weight (lbs.)	TEMCo ID
5	4.04	SOO296
10	8.07	SOO297
15	12.11	SOO298
20	16.14	SOO299
25	20.18	SOO300
30	24.21	SOO301
35	28.25	SOO302
40	32.28	SOO303
50	40.35	SOO304
65	52.46	SOO305
75	60.53	SOO306
85	68.6	SOO307
100	80.7	SOO308
125	100.88	SOO309
150	121.05	SOO310
175	141.23	SOO311
200	161.4	SOO312
225	181.58	SOO313
250	201.75	SOO314
300	242.1	SOO315
400	322.8	SOO316
500	403.5	SOO317
1000	807	SOO318

8/3

Feet per pound: 2.27
Amps per conductor: 40
Conductor stranding: 65 strands each
Insulation thickness: 0.05 in.
Nominal outside diameter: 0.69 in.

Length (ft.)	Weight (lbs.)	TEMCo ID
5	2.2	SOO158
10	4.4	SOO159
15	6.6	SOO160
20	8.8	SOO161
25	11	SOO162
30	13.2	SOO163
35	15.4	SOO164
40	17.6	SOO165
50	22	SOO166
65	28.6	SOO167
75	33	SOO168
85	37.4	SOO169
100	44	SOO170
125	55	SOO171
150	66	SOO172
175	77	SOO173
200	88	SOO174
225	99	SOO175
250	110	SOO176
300	132	SOO177
400	176	SOO178
500	220	SOO179
1000	440	SOO180

8/4

Feet per pound: 1.98
Amps per conductor: 28
Conductor stranding: 65 strands each
Insulation thickness: 0.05 in.
Nominal outside diameter: 0.76 in.

Length (ft.)	Weight (lbs.)	TEMCo ID
5	2.53	SOO043
10	5.06	SOO044
15	7.59	SOO045
20	10.12	SOO046
25	1.65	SOO047
30	15.18	SOO048
35	17.71	SOO049
40	20.24	SOO050
50	25.3	SOO051
65	32.89	SOO052
75	37.96	SOO053
85	43.02	SOO054
100	50.61	SOO055
125	63.26	SOO056
150	75.91	SOO057
175	88.56	SOO058
200	101.21	SOO059
225	113.87	SOO060
250	126.52	SOO061
300	151.82	SOO062
400	202.43	SOO063
500	253.04	SOO064
1000	506.07	SOO065