Enter the conductor temperature, ambient temperature, change in conductor temperatures, conductor resistance, loss increment due to proximity effects, and the thermal resistance between the conductor and ambient into the calculator to determine the wire ampacity.
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Wire Ampacity Formula
The following formula is used to calculate a wire ampacity.
- I is the ampacity (kiloamps)
- Tc is the conductor temperature (deg C)
- Ta is the ambient temperature (deg C)
- Delta T is the change in temperature of the conductor due to dielectric loss (deg C)
- Rdc is the conductor DC resistance (microohms/foot)
- Yc is the loss increment due to conductor skin effects
- Rca is the thermal resistance between the conductor & ambient (thermal ohm feet)
Wire Ampacity Definition
A wire ampacity is defined as the maximum current that a conductor can carry continuously without exceeding the temperature rating.
How to calculate wire ampacity?
First, determine the conductor temperature. For this example, the conductor temperature is 30C.
Next, determine the ambient temperature. This is found to be 10C.
Next, determine the change in temperature of the conductor due to dielectric loss. This is measured to be 5C.
Next, calculate the conductor DC resistance. This is calculated to be 20 microohms/foot.
Next, determine the loss increment due to skin effects. This is found to be .85.
Next, find the thermal resistance between the conductor and ambient. This is determined to be 4 thermal ohm feet.
Finally, calculate the wire ampacity using the formula.
I = .31835 kilo amps.