CUSTOMER REQUEST:

Customers often ask us how to choose the right conductor cross-section based on the nominal current capacity of their application.

Customers often ask us How to choose the right conductor cross-section based on the rated current capacity of its application.

OUR EXPLANATION:

Any conductor carrying current experiences heating, which in turn leads to thermal dissipation. More precisely, a combination of heat dissipation phenomena occurs: conduction, convection, and radiation. The final temperature of the conductor, after continuous current flow, is influenced by:

• la geometric shape of the section (width/thickness ratio)
• the construction method or full or in sheets
• the presence or absence of insulating coating
• the value itself of resistivity (inverse of conductivity)

For laminated conductors, such as Coflex®, an additional correction factor is included in the calculation to account for the skin effect (the tendency of AC current to concentrate near the surface of a conductor) and proximity effect. The type of current—AC or DC—also plays a role in overheating, particularly as the conductor size increases. However, we can state that AC current is more demanding in terms of thermal stress, meaning that ampacity values specified for AC are also valid for DC.

Finally, the ambient temperature, although to a lesser extent, also influences the current carrying capacity. Standards generally assume an ambient temperature of 35°C. For this reason, ampacity tables display different values based on the permitted temperature rise of the conductor, assuming the same ambient temperature.

Aluminum bars, having approximately 30% lower conductivity than copper bars, have a lower current-carrying capacity. However, they offer a weight reduction that, depending on the case, can reach up to 70%.