DC Copper Wire and AC Copper Wire Rules and Guide
Advanced Power Products recognizes that weekend electricians, and others who are not intimately familiar with the electric code, are usually not adept at the difference between copper and aluminum wire. Let alone the voltage drops over such wire in lengths. So we have put together a down and dirty guide.
DC - Copper wire should be stranded to reduce the resistance and allow flexibility at MUCH larger THICKNESSES. This allows these wires to carry high amperages at lower voltages. BD Batteries chooses to supply it's customers with the highest grade welding wire for DC applications as it is tough, shielded for safety, and designed to carry larger loads.
AC - AC Current can be carried on either Copper or Aluminum Wire, and the individual strands are usually thicker. The wire can be a single strand as the voltages are much higher than in many DC systems and the frequency modulations (HZ) help to "MOVE" the electricity along these thicker wires. However, to maintain the ability to bend, multiple larger strands are used to ease production, and installation.
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DC resistance
As long as the current density is totally uniform in the conductor, the DC resistance R of a conductor of regular cross section can be computed as
Where:
l is the length of the conductor, measured in meters
A is the cross-sectional area, measured in square meters
p(Greek: rho) is the electrical resitivity (also called specific electrical resistance)
Copper Electrical resistivity (microohm/cm)
1.678
Ohms of resistance in a material can be measured by a multimeter over a wire. Resistance is a measure of the material's ability to oppose the flow of electric current.
For practical reasons, almost any connection to a real conductor will not show perfect current density, or is not totally uniform. However, this formula still provides a good approximation for long thin conductors such as wires.
Calculate Voltage Drop in WireTo calculate voltage drop, plug in the values: V = DIR/1000
Where I is the amperage,
R is from the ohms/10' X 100 column left,
and D is the total distance the current travels
(don't forget to add the length of the neutral and hot together - ie: usually double cable length). Design rules in the CEC call for a maximum voltage drop of 6% (7V on 120V circuit).
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Load Carrying Capacities or Ampacities
In part from Reference Data for Engineers: Radio, Electronics, Computer and Communications 7th Ed
At 20 C
- De-rate with +0.00393 per °C - wire carrying current capacity sitting in the insulation and conduit will not be at 20 °C You will want to derate to at least the temperature rating of your insulation. Resistance listed here are not trade maxima - most wire that is soft or annealed will be slightly higher. Resistance of hard-drawn copper is slightly greater - 2 - 3%. Stranded wire may also be higher.
| AWG
| Dia Inch
| Cir Mil
| Dia cm
| Area Inch2
| lb/kft
| ohms
/kft
| Ohms
/km
| CU Max
free-air
Amps
| CU Max
enclosed
Amps
|
| 32
| 0.008
| 63.2
| 0.020
| 4.964E-05
| 0.19
| 164.1
| 538.4
| .53
| 0.32
|
| 30
| 0.010
| 100.5
| 0.025
| 7.894E-05
| 0.30
| 103.2
| 338.6
| .86
| 0.52
|
| 28
| 0.013
| 159.8
| 0.032
| 1.255E-04
| 0.48
| 64.9
| 212.9
| 1.4
| 0.83
|
| 26
| 0.016
| 254.1
| 0.040
| 1.996E-04
| 0.77
| 40.81
| 133.9
| 2.2
| 1.3
|
| 24
| 0.020
| 404.0
| 0.051
| 3.173E-04
| 1.22
| 25.67
| 84.22
| 3.5
| 2.1
|
| 22
| 0.025
| 642.4
| 0.064
| 5.046E-04
| 1.94
| 16.14
| 52.95
| 7.0
| 5.0
|
| 20
| 0.032
| 1,021.5
| 0.081
| 8.023E-04
| 3.09
| 10.15
| 33.30
| 11.0
| 7.5
|
| 18
| 0.040
| 1,624.3
| 0.102
| 1.276E-03
| 4.92
| 6.385
| 20.95
| 16
| 10
|
| 16
| 0.051
| 2,582.7
| 0.129
| 2.028E-03
| 7.82
| 4.016
| 13.18
| 22
| 13
|
| 14
| 0.064
| 4,106.7
| 0.163
| 3.225E-03
| 12.43
| 2.525
| 8.284
| 32
| 17
|
| 12
| 0.081
| 6,529.9
| 0.205
| 5.129E-03
| 19.77
| 1.588
| 5.210
| 41
| 23
|
| 10
| 0.102
| 10,383.0
| 0.259
| 8.155E-03
| 31.43
| 1.215
| 3.985
| 55
| 33
|
| 8
| 0.128
| 16,509.7
| 0.326
| 1.297E-02
| 49.98
| 0.998
| 3.274
| 73
| 46
|
| 6
| 0.162
| 26,251.4
| 0.412
| 2.062E-02
| 79.46
| 0.395
| 1.296
| 101
| 60
|
| 4
| 0.204
| 41,741.3
| 0.519
| 3.278E-02
| 126.35
| 0.248
| 0.8136
| 135
| 80
|
| 2
| 0.258
| 66,371.3
| 0.654
| 5.213E-02
| 200.91
| 0.156
| 0.5118
| 181
| 100
|
| 1
| 0.289
| 83,692.7
| 0.735
| 6.573E-02
| 253.34
| 0.123
| 0.4035
| 211
| 125
|
| 0
| 0.325
| 105,534.5
| 0.825
| 8.289E-02
| 319.46
| 0.0983
| 0.3225
| 245
| 150
|
| 00
| 0.365
| 133,076.5
| 0.927
| 1.045E-01
| 402.83
| 0.0779
| 0.2556
| 283
| 175
|
| 000
| 0.410
| 167,806.4
| 1.040
| 1.318E-01
| 507.96
| 0.0618
| 0.2028
| 328
| 200
|
| 0000
| 0.460
| 211,600.0
| 1.168
| 1.662E-01
| 640.53
| 0.04901
| 0.1608
| 380
| 225
|
- A second version of the above table with 60°C trade derating - (effects ohms/kft and ohms/km.)
Max ambient 60°C
| AWG
| Dia Inch
| Cir Mil
| Dia cm
| Area Inch2
| lb/kft
| ohms
/kft
| Ohms
/km
| CU Max
free-air
Amps
| CU Max
enclosed
Amps
|
| 32
| 0.008
| 63.2
| 0.020
| 4.964E-05
| 0.19
| 199.587
| 654.613
| .53
| 0.32
|
| 30
| 0.010
| 100.5
| 0.025
| 7.894E-05
| 0.30
| 125.521
| 411.690
| .86
| 0.52
|
| 28
| 0.013
| 159.8
| 0.032
| 1.255E-04
| 0.48
| 78.941
| 258.915
| 1.4
| 0.83
|
| 26
| 0.016
| 254.1
| 0.040
| 1.996E-04
| 0.77
| 49.647
| 162.833
| 2.2
| 1.3
|
| 24
| 0.020
| 404.0
| 0.051
| 3.173E-04
| 1.22
| 31.223
| 102.407
| 3.5
| 2.1
|
| 22
| 0.025
| 642.4
| 0.064
| 5.046E-04
| 1.94
| 19.636
| 64.404
| 7.0
| 5.0
|
| 20
| 0.032
| 1,021.5
| 0.081
| 8.023E-04
| 3.09
| 12.349
| 40.504
| 11.0
| 7.5
|
| 18
| 0.040
| 1,624.3
| 0.102
| 1.276E-03
| 4.92
| 7.767
| 25.473
| 16
| 10
|
| 16
| 0.051
| 2,582.7
| 0.129
| 2.028E-03
| 7.82
| 4.884
| 16.020
| 22
| 13
|
| 14
| 0.064
| 4,106.7
| 0.163
| 3.225E-03
| 12.43
| 3.072
| 10.075
| 32
| 17
|
| 12
| 0.081
| 6,529.9
| 0.205
| 5.129E-03
| 19.77
| 1.932
| 6.336
| 41
| 23
|
| 10
| 0.102
| 10,383.0
| 0.259
| 8.155E-03
| 31.43
| 1.215
| 3.985
| 55
| 33
|
| 8
| 0.128
| 16,509.7
| 0.326
| 1.297E-02
| 49.98
| 0.764
| 2.506
| 73
| 46
|
| 6
| 0.162
| 26,251.4
| 0.412
| 2.062E-02
| 79.46
| 0.481
| 1.576
| 101
| 60
|
| 4
| 0.204
| 41,741.3
| 0.519
| 3.278E-02
| 126.35
| 0.302
| 0.991
| 135
| 80
|
| 2
| 0.258
| 66,371.3
| 0.654
| 5.213E-02
| 200.91
| 0.190
| 0.623
| 181
| 100
|
| 1
| 0.289
| 83,692.7
| 0.735
| 6.573E-02
| 253.34
| 0.151
| 0.494
| 211
| 125
|
| 0
| 0.325
| 105,534.5
| 0.825
| 8.289E-02
| 319.46
| 0.120
| 0.392
| 245
| 150
|
| 00
| 0.365
| 133,076.5
| 0.927
| 1.045E-01
| 402.83
| 0.095
| 0.311
| 283
| 175
|
| 000
| 0.410
| 167,806.4
| 1.040
| 1.318E-01
| 507.96
| 0.075
| 0.247
| 328
| 200
|
| 0000
| 0.460
| 211,600.0
| 1.168
| 1.662E-01
| 640.53
| 0.060
| 0.196
| 380
| 225
|
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