Cable ampacity or current carrying capacity is the maximum current that the cable can carry continuously at maximum operating temperature.
Current passing through a cable faces electrical resistance and produces heat. The temperature of the conductor rises depending on the current value. Here comes the cable ampacity.
What determines conductor ampacity?
Cable current depends mainly on how much temperature it can handle without failure! The maximum temperature is affected by many factors, like cable laying method, soil thermal resistivity, laying depth underground and other factors which affect current carrying capacity of the cable, Other factors are listed below:
- Conductor material.
- Insulation around the cable. i.e XLPE or PVC, XLPE insulated cables can carry more current than PVC insulated ones.
- Laying method of the cable. i.e in air, underground or in duct.
- Laying in Trefoil or flat formation.
- The ambient temperature.
- Soil thermal resistivity.
- Burial depth underground.
- Duct inner diameter for cables in duct.
- Number of cables in the same laying path.
Some of the above factors are fixed like cable material and insulation, while others can vary from one application to another like ambient temperature. Cables are manufactured for specific working conditions, if the working conditions are not the same as the designed ones, we apply correction for cable ampacity. The correction factors are known as derating factors.
I have written a detailed article about cable correction factors, Read it for more information here.
Where to find Cable ampacity Tables?
Each cables manufacturer has a products catalog. This catalog contains data and tables of the cable electrical and physical properties.
Voltage drop, Derating factors, short circuit, table of ampacity and more electrical data are in these tables.
One of the most important tables that every one who works with cables needs it regularly is the ampacity or current carrying capacity tables.
In the table we find cable cross section area, in the firs column then resistance and current that each cable size can carry. There are three current values for each cable size because, this current value affected by the laying method and other correction factors.
If you don’t have cable catalogues, don’t worry, I have the solution for you. Continue reading below paragraph.
Cables Ampacity, Android app for electricians
I have created a FREE android app to help you when choosing a cable. I call it “Cables Tables“, because cables tables are used in designing all electrical loads in work site so, its important to have cable rating tables on your hands.
This app has cables most common tables and data we, engineers and electricians, need everyday, like ampacity , voltage drop, derating and short circuit tables.
The app is 100% free. However it has Ads free paid version, you can switch to it later after trying the free version.
Install My “Cables Tables” app free now.
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