Ampacity is an electrical term used interchangeably with the term current-carrying capacity. These words refer to the maximum load of current a cable can carry. Ampacity can vary greatly from one cable to the next. The variance can be based on internal factors, external factors, or both.
To understand this, it may be helpful to have a basic understanding of electrical conduction. Copper and aluminum are considered good conductors of heat. This means that large amounts of electricity can travel through them from one point to another without them disintegrating. Of the two, copper is the better conductor. This is why it is so commonly used in electric cables.
The electricity that moves through a copper wire is actually a group of electrons being pushed by voltage. The higher the voltage, the more electrons that can be sent flowing through the wire. Ampacity refers to the maximum number of electrons that can be pushed.
It could be easy to mistakenly think the maximum amount of electricity that can flow through copper is equal to the ampacity of the cable it is in. This conclusion, however, is false. There are several factors that can result in a cable having lower capabilities than its inner wire.
A cable’s conductor is insulated. If it wasn’t, the part of the cable that can be touched, also known as the jacket, would burn up. When current travels within that insulation, heat is generated. That insulation can tolerate less heat than the conductor inside. If this is ignored, the insulation and perhaps the entire cable will burn up.
Ampacity is also affected by external factors. A cable lying in the sun is also impacted from a high level of exterior heating. The cable must be able to withstand this and the heat generated by the current flowing through it. A cable in a cool area, such as underground, can have a higher ampacity because the external temperatures can help lower the cable’s temperature. The amount of heat a cable can sustain while functioning normally and safely is its temperature rating.
Another factor that affects ampacity is the size of the conductor. When carrying electricity, a piece of copper is like a tunnel. The smaller the tunnel, the more limited the flow. If a wider tunnel is made available, the flow can increase. Cables that are larger in diameter tend to be that way because the conductor inside is larger. This results in higher ampacity.