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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 conductor wire can be increased until the heat generated reaches the melting temperature of 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.

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

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 Conductors:

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

Taking into account all the variables involved, no simple chart of current ratings can be developed and used as the final word when designing a system where amperage ratings can become critical.

The chart shows the current required to raise the temperatures of single insulated conductor in free air (30C ambient) to the limits of various insulation types. The fallowing table gives a derating factor to be used when the conductors are bundled. These charts should only be used as a guide when attempting to establish current ratings on conductor and cable.

DERATING FACTORS FOR BUNDLED CONDUCTORS

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

Amperes




Insulation
Materials
Polyethylene
Neoprene
Polyurethane
Polyvinylchloride
(Semi-Rigid)


Polypropylene
Polyethylene
(High Density)


Polyvinylchloride
PVC (Irradiated)
Nylon
Kynar (135C)
Polyethylene
(Crosslinked)
Thermoplastic
Elastomers
Kapton
PTFE
FEP
PFA
Silicone
Copper Temp. 80C 90C 105C 125C 200C
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
Single Conductor in Free Air 30C Ambient Temp.