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.
Example Problem
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 the ambient. This is determined to be four thermal ohm feet.
Finally, calculate the wire ampacity using the formula.
I = .31835 kilo amps.
FAQ
What factors affect wire ampacity?
Wire ampacity can be affected by several factors including the conductor material, the temperature of the conductor, the ambient temperature, the presence of dielectric loss, the DC resistance of the conductor, skin effects, and the thermal resistance between the conductor and its surroundings. These factors can influence the maximum current a wire can carry without exceeding its temperature rating.
How does ambient temperature affect wire ampacity?
Ambient temperature plays a crucial role in determining wire ampacity. A higher ambient temperature can reduce the ampacity of a wire because it decreases the temperature difference between the wire and its surroundings, potentially leading to overheating. Conversely, a lower ambient temperature can increase the ampacity by allowing the wire to dissipate heat more effectively.
What is the significance of skin effects on wire ampacity?
Skin effects refer to the tendency of alternating current (AC) to flow near the surface of a conductor rather than uniformly throughout its cross-section. This effect increases the effective resistance of the conductor at higher frequencies, leading to additional losses and heating. As a result, skin effects can significantly reduce the ampacity of a wire by limiting the maximum current it can carry without overheating.
