White Paper - Determine Wire Gauge Insulation Type for a System Current Requirement Rev A

8/3/2019 White Paper - Determine Wire Gauge Insulation Type for a System Current Requirement Rev A

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Technical Paper

Determine wire gauge (AWG) &

insulation type for a system current(amperes) requirement

Ray-Q Ltd.

Gilboa St.

Ben-Gurion Airport City

70100, Israel


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Copyright Ray-Q Ltd.

Gilboa St.Ben-Gurion Airport City

70100, Israel

Tel: (972) 3 9753333Fax: (972) 3 9753300

DETERMINE WIRE GAUGE (AWG) &

INSULATION TYPE FOR A SYSTEMCURRENT (AMPERES) REQUIREMENT

08081//

Rev. A

Page 2 of 15

List of Revisions

Rev. Change Description DateNew First Issue 02/09

A Update 08/11


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08081//

Rev. A

Page 3 of 15

Can a conductor rated at 10 amps carry 10 amps? Maybe yes probably not. Thereason lies in the test conditions used to rate the conductor. If these conditions donot adequately reflect application conditions, actual allowable current levels may

be lower than specified levels.For example, many manufacturers test a single conductor in air. This gives anaccurate measure of the basic current-carrying capacity of the conductor. Use theconductor alone in air and it can certainly carry 10 amps. Use it in a multi positionconductors surrounded by other current-carrying conductor or in high ambienttemperatures and the conductor should carry less current.

This technical paper was composed in order to help the designer set theappropriate current level and specified the current carrying capacity (ampacity) ofa wire or harness.


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08081//

Rev. A

Page 4 of 15

The ampacity is the maximum amount of current an insulated conductor can carrywithout heating beyond a safe limit. Major influences are:

1. Conductor Size: The larger the cross section area, the greater the currentcarrying capacity.

2. Temperature Rating: Wires and cables are rated for continuous operationtemperature. The wire temperature ratings in this technical paper are inaccording to common applications:

Marine Application: 90C and 105C

Ground Application: 125C and 150C

Airborne Application: 150C and 200C

Space application: 200C

3. Conductor material: Ampacity is affected by conductivity. Thus theampacity of an aluminum conductor is approximately 80% that of the samesize copper conductor.

4. Insulation Material: The amount of heat generated should never exceedthe maximum temperature rating of the insulation. Therefore, the higherthe temperature rating of the insulation, the greater current carryingcapacity of the wire.

5. Ambient Temperature: The higher the ambient temperature, the less heat

required to exceed the maximum temperature rating of the insulation.6. Installation Method: In air, conduit, duct, tray or direct burial. Bundling,

stacking and spacing all affect heat dissipation.

7. Installation Environment: Heat dissipation by conduction, convection,forced air flow, altitude, air conditioning etc.

8. Number of conductors: Single conductors have a higher ampacity ratingthan equivalent size conductors bundled in a cable.Heat dissipation is lessened as the number of individually insulatedconductors, bundled together, is increased.

9. Amperage: Heat increase is not linear; it varies as the square of theapplied current.


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08081//

Rev. A

Page 5 of 15

These many factors make it impossible to construct a general chart for ampacity.

The values shown in Table1 are MAXIMUM for a single conductor in free air,based on ambient temperature of 30C at sea level, enabling a temperature risefit for different wire types.

For cable or harness with two (2) or three (3) conductors use Table2.

For cable or harness with more than three (3) conductors, make circuit analysisfor the bundle to define the percentages of wires in the bundle that carrying powercurrent nearly at or up to capacity. Use correction factor in Table 4 to correct thevalues in Table1.

For actual use temperatures above an ambient temperature of 30C, reduce themaximum ampacity by use of correction factor in Table 3 to correct the values inTable1 and Table2.

For altitude above sea level, reduce the maximum ampacity by use of correctionfactor in Table 5 to correct the values in Table1 and Table2.


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08081//

Rev. A

Page 6 of 15

Table1: Lead Wire Current Carrying Capacity(Amperes per Conductor)

AWG 90C 105C 125C 150C 200C

30 3 3 3 3 4

28 4 4 5 5 6

26 5 5 6 6 7

24 7 7 8 8 10

22 10 11 12 14 16

20 13 14 15 18 2118 18 20 22 24 28

16 22 25 26 28 32

14 30 33 37 42 50

12 40 45 50 55 68

10 55 60 65 75 88

8 80 90 97 106 124

6 105 121 131 155 165

4 140 160 172 190 2202 190 215 232 255 293

1 220 247 266 293 344

1/0 260 286 309 339 399

2/0 300 329 355 390 467

3/0 350 380 410 451 546

4/0 405 446 481 529 629

Note:

1. Values (amperes) shown in this table are maximum for a single conductorin free air with an assumed ambient temperature of 30C, and altitude atsea level.


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08081//

Rev. A

Page 7 of 15

Table2: Current Carrying Capacity of 2 or 3 conductors(Amperes per Conductor)

AWG 90C 105C 125C 150C 200C

30 1 2 2 2 3

28 2 3 3 3 4

26 3 3 4 4 4

24 4 4 5 5 6

22 6 7 8 9 10

208

9

10

13

15

18 14 15 16 17 20

16 18 19 20 22 25

14 25 29 31 34 36

12 30 36 39 43 45

10 40 46 50 55 60

8 55 64 69 76 83

6 75 81 87 96 110

4 95 109 118 120 125

2 130 143 154 160 171

1 150 168 181 186 197

1/0 170 193 208 215 229

2/0 195 229 247 251 260

3/0 225 263 284 288 297

4/0 260 301 325 332 346

Notes:

1. Current carrying capacity of not more than three (3) conductors within acable, tubing, conduit or bundled together.

2. The values (amperes) shown in this table are maximum at an assumedambient room temperature of 30C at sea level altitude.


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08081//

Rev. A

Page 8 of 15

Table 3: Ambient temperatures Correction factors forTable1 & Table2

AmbientTemperature

(C)

Insulation Temperature Rating

90C 105C 125C 150C 200C

31 35 0.96 1.00 1.00 1.00 1.00

36 40 0.91 1.00 1.00 1.00 1.00

41 45 0.87 0.93 0.94 0.95 0.97

46 50 0.82 0.93 0.94 0.95 0.97

51 55 0.76 0.85 0.87 0.90 0.94

56 60 0.71 0.85 0.87 0.90 0.94

61 70 0.58 0.76 0.80 0.85 0.90

71 80 0.41 0.65 0.73 0.80 0.87

81 90 0.53 0.64 0.74 0.83

91 100 0.38 0.54 0.67 0.79

101 120 0.24 0.52 0.71

121 140 0.30 0.61

141 160 0.50

161 - 180 0.35

Note:

1. For ambient temperatures over 30C, multiply the ampacities shown inTable1 or Table2 by the appropriate correction factor to determine themaximum allowable load current.


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08081//

Rev. A

Page 9 of 15

Table 4: More than three conductor correction factor forTable1

Number ofConductors

Bundle Loading Percentage

20% 40% 60% 80% 100%

4 thru 6 0.85 0.75 0.70 0.65 0.60

7 thru 9 0.80 0.65 0.60 0.55 0.50

10 thru 20 0.65 0.55 0.55 0.40 0.35

21 thru 30 0.60 0.45 0.40 0.35 0.30

31 thru 40 0.55 0.40 0.35 0.30 0.25

41 and above 0.50 0.35 0.30 0.30 0.25

Note:

1. If more than three (3) conductors are in a cable, tubing, and conduit orbundled together; the values given in Table1 must be reduced using theabove correction factor.

2. Make circuit analysis for the bundle to define the percentages of wires inthe bundle that carrying power current nearly at or up to capacity.


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08081//

Rev. A

Page 10 of 15

Table 5: Above sea level correction factor forTable1 & Table2

Altitude (ft) Correction factor

1,000 thru 5,000 0.975

5,001 thru 10,000 0.950

10,001 thru 15,000 0.925

15,001 thru 20,000 0.900

20,001 thru 30,000 0.875

30,001 thru 40,000 0.850

40,001 thru 50,000 0.825

50,001 thru 60,000 0.800

60,001 thru 70,000 0.775

70,001 thru 80,000 0.750

80,001 thru 90,000 0.725

90,001 thru 100,000 0.700

100,001 and above 0.600

Vacuum 0.500

Note:

1. If above sea level the values given in Table1 & Table2 must be reducedusing the above correction factor


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08081//

Rev. A

Page 11 of 15

Example:

Application: airborne

System Maximum Current: 8 amps.

Cable: 12 wires bundle, 6 wires carrying power currents nearly at or up tocapacity.

Ambient temperature: 70C.

Altitude: 60,000 ft

Step 1:

Refer to Table1 determine the AWG and the current of the wire required for theapplication. Since the application is airborne and the required wire temperature

rate is 150C the free air rating for size #22 is 14 amps, and the free air rating forsize #20 is 18 amps.

Step 2:

Refer to Table 4 ("More than three conductor correction factors"). For a 12conductor bundle use "10 thru 20" (on the first column). Since there are 12 wiresin the bundle and only 6 wires carrying power currents nearly at or up to capacity,the bundle loading percentage would be:

12 wires / 6 wires = 50%

To be on the safe side the correction factor will calculate for Bundle LoadingPercentage of 60%. Therefore the correction factor to use would be 0.55.

Alternate #1

Table1 state 14 amps for 22 AWG @ 150C, but when derated for bundle sizethe actual rating is:

22 AWG 14 [Amps] X 0.55 [correction factor] = 7.7 Amps.

The result gives out a rating of 7.7 Amps which is insufficient for the application.

Alternate #2


20 AWG 18 [Amps] X 0.55 [correction factor] = 9.9 Amps.

The result gives out a rating of 9.9 Amps which is sufficient for the application.


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08081//

Rev. A

Page 12 of 15

Alternate #3


18 AWG 24 [Amps] X 0.55 [correction factor] = 13.2 [Amps].


Step 3:

Refer to Table 3 Ambient temperatures Correction factors, look for70C. Sincethat is the temperature at which the application will be operating and the wiretemperature rating is 150C. Determine that the wire correction factor to be 0.85.

Alternate #1

Calculate the derated ampacity of the 20 AWG wire by multiplying with thecorrection factor from Table 3:

20 AWG 9.9 [Amps] X 0.85 [correction factor] = 8.415 Amps.


Alternate #2


18 AWG 13.2 [Amps] X 0.85 [correction factor] = 11.22 Amps.



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08081//

Rev. A

Page 13 of 15

Step 4:

Refer to Table 5 Above sea level correction factor look for 60,000 feet (on thefirst column). Since that is the temperature at which the application will beoperating. Determine that the wire correction factor to 80%.

Alternate #1


20 AWG 8.415 [Amps] X 0.8 [correction factor] = 6.732 [Amps].

The result gives out a rating of 6.732 Amps which is insufficient for theapplication.

Alternate #2


18 AWG 11.22 [Amps] X 0.8 [correction factor] = 8.976 [Amps].



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08081//

Rev. A

Page 14 of 15

Appendix A: Charts

METRIC/AWG WIRE SIZE EQUIVALENTS

In Europe wire and cable sizes are expressed in mm2 (cross sectional area),while in US the AWG (American Wire Gauge) is the standard system used forboth solid and strand conductors. See below for the cross reference scheme.

Sq. MM AWG

0.05 30

0.08 280.14 26

0.25 24

0.34 22

0.50 20

0.75 18

1.00 17

1.50 16

2.50 14

4.00 126.00 10

10.00 8

16.00 6

25.00 4

35.00 2

50.00 1

70.00 2/0

95.00 3/0

120.00 4/0

Note:

1. Cross references are approximated


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08081//

Rev. A

Fahrenheit (F) to Celsius (C) conversion

F C F C F C F C F C F C F C F C

1.0 -17.2 51.0 10.6 101.0 38.3 151.0 66.1 201.0 93.9 251.0 121.7 301.0 149.4 351.0 177.2

2.0 -16.7 52.0 11.1 102.0 38.9 152.0 66.7 202.0 94.4 252.0 122.2 302.0 150.0 352.0 177.8

3.0 -16.1 53.0 11.7 103.0 39.4 153.0 67.2 203.0 95.0 253.0 122.8 303.0 150.6 353.0 178.3

4.0 -15.6 54.0 12.2 104.0 40.0 154.0 67.8 204.0 95.6 254.0 123.3 304.0 151.1 354.0 178.9

5.0 -15.0 55.0 12.8 105.0 40.6 155.0 68.3 205.0 96.1 255.0 123.9 305.0 151.7 355.0 179.4

6.0 -14.4 56.0 13.3 106.0 41.1 156.0 68.9 206.0 96.7 256.0 124.4 306.0 152.2 356.0 180.0

7.0 -13.9 57.0 13.9 107.0 41.7 157.0 69.4 207.0 97.2 257.0 125.0 307.0 152.8 357.0 180.6

8.0 -13.3 58.0 14.4 108.0 42.2 158.0 70.0 208.0 97.8 258.0 125.6 308.0 153.3 358.0 181.1

9.0 -12.8 59.0 15.0 109.0 42.8 159.0 70.6 209.0 98.3 259.0 126.1 309.0 153.9 359.0 181.7

10.0 -12.2 60.0 15.6 110.0 43.3 160.0 71.1 210.0 98.9 260.0 126.7 310.0 154.4 360.0 182.2

11.0 -11.7 61.0 16.1 111.0 43.9 161.0 71.7 211.0 99.4 261.0 127.2 311.0 155.0 361.0 182.8

12.0 -11.1 62.0 16.7 112.0 44.4 162.0 72.2 212.0 100.0 262.0 127.8 312.0 155.6 362.0 183.3

13.0 -10.6 63.0 17.2 113.0 45.0 163.0 72.8 213.0 100.6 263.0 128.3 313.0 156.1 363.0 183.9

14.0 -10.0 64.0 17.8 114.0 45.6 164.0 73.3 214.0 101.1 264.0 128.9 314.0 156.7 364.0 184.4

15.0 -9.4 65.0 18.3 115.0 46.1 165.0 73.9 215.0 101.7 265.0 129.4 315.0 157.2 365.0 185.0

16.0 -8.9 66.0 18.9 116.0 46.7 166.0 74.4 216.0 102.2 266.0 130.0 316.0 157.8 366.0 185.6

17.0 -8.3 67.0 19.4 117.0 47.2 167.0 75.0 217.0 102.8 267.0 130.6 317.0 158.3 367.0 186.1

18.0 -7.8 68.0 20.0 118.0 47.8 168.0 75.6 218.0 103.3 268.0 131.1 318.0 158.9 368.0 186.7

19.0 -7.2 69.0 20.6 119.0 48.3 169.0 76.1 219.0 103.9 269.0 131.7 319.0 159.4 369.0 187.2

20.0 -6.7 70.0 21.1 120.0 48.9 170.0 76.7 220.0 104.4 270.0 132.2 320.0 160.0 370.0 187.8

21.0 -6.1 71.0 21.7 121.0 49.4 171.0 77.2 221.0 105.0 271.0 132.8 321.0 160.6 371.0 188.3

22.0 -5.6 72.0 22.2 122.0 50.0 172.0 77.8 222.0 105.6 272.0 133.3 322.0 161.1 372.0 188.9

23.0 -5.0 73.0 22.8 123.0 50.6 173.0 78.3 223.0 106.1 273.0 133.9 323.0 161.7 373.0 189.4

24.0 -4.4 74.0 23.3 124.0 51.1 174.0 78.9 224.0 106.7 274.0 134.4 324.0 162.2 374.0 190.0

25.0 -3.9 75.0 23.9 125.0 51.7 175.0 79.4 225.0 107.2 275.0 135.0 325.0 162.8 375.0 190.6

26.0 -3.3 76.0 24.4 126.0 52.2 176.0 80.0 226.0 107.8 276.0 135.6 326.0 163.3 376.0 191.1

27.0 -2.8 77.0 25.0 127.0 52.8 177.0 80.6 227.0 108.3 277.0 136.1 327.0 163.9 377.0 191.7

28.0 -2.2 78.0 25.6 128.0 53.3 178.0 81.1 228.0 108.9 278.0 136.7 328.0 164.4 378.0 192.2

29.0 -1.7 79.0 26.1 129.0 53.9 179.0 81.7 229.0 109.4 279.0 137.2 329.0 165.0 379.0 192.8

30.0 -1.1 80.0 26.7 130.0 54.4 180.0 82.2 230.0 110.0 280.0 137.8 330.0 165.6 380.0 193.3

31.0 -0.6 81.0 27.2 131.0 55.0 181.0 82.8 231.0 110.6 281.0 138.3 331.0 166.1 381.0 193.9

32.0 0.0 82.0 27.8 132.0 55.6 182.0 83.3 232.0 111.1 282.0 138.9 332.0 166.7 382.0 194.4

33.0 0.6 83.0 28.3 133.0 56.1 183.0 83.9 233.0 111.7 283.0 139.4 333.0 167.2 383.0 195.0

34.0 1.1 84.0 28.9 134.0 56.7 184.0 84.4 234.0 112.2 284.0 140.0 334.0 167.8 384.0 195.6

35.0 1.7 85.0 29.4 135.0 57.2 185.0 85.0 235.0 112.8 285.0 140.6 335.0 168.3 385.0 196.1

36.0 2.2 86.0 30.0 136.0 57.8 186.0 85.6 236.0 113.3 286.0 141.1 336.0 168.9 386.0 196.7

37.0 2.8 87.0 30.6 137.0 58.3 187.0 86.1 237.0 113.9 287.0 141.7 337.0 169.4 387.0 197.2

38.0 3.3 88.0 31.1 138.0 58.9 188.0 86.7 238.0 114.4 288.0 142.2 338.0 170.0 388.0 197.8

39.0 3.9 89.0 31.7 139.0 59.4 189.0 87.2 239.0 115.0 289.0 142.8 339.0 170.6 389.0 198.3

40.0 4.4 90.0 32.2 140.0 60.0 190.0 87.8 240.0 115.6 290.0 143.3 340.0 171.1 390.0 198.9

41.0 5.0 91.0 32.8 141.0 60.6 191.0 88.3 241.0 116.1 291.0 143.9 341.0 171.7 391.0 199.4

42.0 5.6 92.0 33.3 142.0 61.1 192.0 88.9 242.0 116.7 292.0 144.4 342.0 172.2 392.0 200.0

43.0 6.1 93.0 33.9 143.0 61.7 193.0 89.4 243.0 117.2 293.0 145.0 343.0 172.8 393.0 200.6

44.0 6.7 94.0 34.4 144.0 62.2 194.0 90.0 244.0 117.8 294.0 145.6 344.0 173.3 394.0 201.1

45.0 7.2 95.0 35.0 145.0 62.8 195.0 90.6 245.0 118.3 295.0 146.1 345.0 173.9 395.0 201.7

46.0 7.8 96.0 35.6 146.0 63.3 196.0 91.1 246.0 118.9 296.0 146.7 346.0 174.4 396.0 202.2

47.0 8.3 97.0 36.1 147.0 63.9 197.0 91.7 247.0 119.4 297.0 147.2 347.0 175.0 397.0 202.8

48.0 8.9 98.0 36.7 148.0 64.4 198.0 92.2 248.0 120.0 298.0 147.8 348.0 175.6 398.0 203.3

49.0 9.4 99.0 37.2 149.0 65.0 199.0 92.8 249.0 120.6 299.0 148.3 349.0 176.1 399.0 203.9

50.0 10.0 100.0 37.8 150.0 65.6 200.0 93.3 250.0 121.1 300.0 148.9 350.0 176.7 400.0 204.4

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White Paper - Determine Wire Gauge Insulation Type for a System Current Requirement Rev A