The size of an electrical cable and its ampacity, or current-carrying capacity, are closely related. The ampacity of a cable is determined by several factors, including its conductor material (usually copper or aluminum), the size of the conductor (gauge), the type of insulation, and the installation conditions.
Following is a basic guide to help you understand the relationship between cable size and amps rating:
Cable Size vs Amps Rating
Cable Gauge (AWG) and Ampacity for Copper Wires:
- 14 AWG: Typically rated for up to 15 amps.
- 12 AWG: Usually suitable for up to 20 amps.
- 10 AWG: Generally good for up to 30 amps.
- 8 AWG: Often used for circuits carrying up to 40 amps.
- 6 AWG: Suitable for up to 55-60 amps.
- 4 AWG: Can typically handle up to 70-85 amps.
- 2 AWG: Used for circuits up to about 95-115 amps.
Cable Gauge (AWG) and Ampacity for Aluminum Wires:
Aluminum wires are generally less conductive than copper, so they carry less current for the same gauge. For instance, a 12 AWG aluminum wire may carry about 15-20 amps, whereas the same gauge in copper can handle 20 amps.
Insulation and Temperature Ratings:
The insulation type and temperature rating of the wire also affect its ampacity. For example, THHN wire, a common type of insulated wire, has different ampacity ratings at different temperatures.
Installation Conditions:
Factors such as the ambient temperature, whether the wire is in a conduit, and the number of conductors bundled together also impact the ampacity. In tighter spaces or higher ambient temperatures, the ampacity of a cable might need to be derated.
Voltage Drop:
For longer cable runs, voltage drop can be a concern. Heavier gauge wires may be needed to ensure that the voltage drop over the length of the run is within acceptable limits, especially for lower voltage systems.
Safety Standards and Codes:
Electrical codes, such as the National Electrical Code (NEC) in the United States, provide detailed tables and guidelines for determining the appropriate wire size for a given ampacity to ensure safety and efficiency in electrical installations.
It’s important to consult the specific ampacity tables like NEC international code and local electrical codes for the precise requirements for your particular application. If you’re not sure, it’s always best to consult with a licensed electrician and engineer. Improperly sized wiring can lead to inefficient electrical operation, overheating, and potential fire hazards.
CABLE SIZE & CURRENT RATING CHART
Following is table showing in picture for cable size and current rating chart for single phase and three phase.
