Current Carrying Capacity of Copper Conductors

Current carrying capacity is defined as the amperage a conductor can carry before melting either the conductor or the insulation.

Heat, caused by an electrical current flowing through a conductor, will determine the amount of current a wire will handle. Theoretically, the amount of current that can be passed through a single bare copper wire can be increased until the heat generated reaches the melting temperature of the copper.

There are many factors which will limit the amount of current that can be passed through a wire. These major determining factors are:

Conductor Size:
The larger the circular mil area, the greater the current capacity.

Insulation:
The amount of heat generated should never exceed the maximum temperature rating of the insulation material.

Ambient Temperature:
The higher the ambient temperature, the less heat required to reach the maximum temperature rating of the insulation.

Conductor Number:
Heat dissipation is lessened as the number of individually insulated conductors, bundled together, is increased.

Installation Conditions:
Restricting the heat dissipation by installing the conductors in conduit, duct, trays or raceways lessens the current carrying Capacity. This restriction can be alleviated somewhat by using proper ventilation methods, forced air cooling, etc.

Taking into account all the variables involved, no simple table of current rating can be developed and used as the final word when designing a system where amperage ratings can become critical. The first table on the next page shows the current required to raise the temperatures of single insulated conductor in free air (30 C ambient) to the limits of various insulation types. The second table on the next page gives a derating factor to be used when the conductors are bundled. These tables should only be used as a guide when attempting to establish current ratings on conductor and cable.



Amperes

Insulation Materials Polyethylene Neoprene Polyurethane Polyvinylchloride (Semi-Rigid) Polypropylene Polyethylene (High Density) Polyvinylchloride PVC (Irradiated) Nylon Kynar (135 C) Polyethylene (Crosslinked) Thermoplastic Elastomers Kapton
PTFE Silicone
Copper Temp. 80 C 90 C 105 C 125 C 200 C
30 AWG 2 3 3 3 4
28 AWG 3 4 4 5 6
26 AWG 4 5 5 6 7
24 AWG 6 7 7 8 10
22 AWG 8 9 10 11 13
20 AWG 10 12 13 14 17
18 AWG 15 17 18 20 24
16 AWG 19 22 24 26 32
14 AWG 27 30 33 40 45
12 AWG 36 40 45 50 55
10 AWG 47 55 58 70 75
8 AWG 65 70 75 90 100
6 AWG 95 100 105 125 135
4 AWG 125 135 145 170 180
2 AWG 170 180 200 225 240
1 AWG   211   265 280
1/0 AWG   245   305 325
2/0 AWG   283   355 370
3/0 AWG   328   410 430
4/0 AWG   380   475 510
Single Conductor in Free Air 30 C Ambient Temperature



Derating Factors for Bundled Conductors

Bundle # Derating Factor (X Amps)
2 - 5 0.8
6 - 15 0.7
16 - 30 0.5
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