| 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 the 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 carrying 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 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 (30°C ambient) to the limits of various Insulation
types.
The following 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. |
