Sumary of Determining Current Carrying Capacity of Conductors:
- The purpose of NFPA 70®, National Electrical Code® (NEC®) is the practical safeguarding of persons and property from the hazards that arise due to the use of electricity.
- Fires resulting from improper wiring have historically been a significant threat ever since electrical systems have been installed within buildings.
- The NEC has established a long history of installation requirements to help prevent fires from occurring within the electrical system.
- One such requirement is to determine how much electrical current a conductor can carry continuously without exceeding the temperature rating of its insulation, or as the NEC refers to it, a conductor’s ampacity.
- However, determining ampacity requires the understanding of a number of other factors that come into play based on how a conductor is used and installed.
- Depending on which conditions of installation and use exist, we find ourselves using a number of tables found throughout the NEC, but in particular, many of them are located in Article 310. There are a multitude of tables that spell out items such as conductor ampacity, temperature correction factors, and adjustment factors.
- So, let’s take a look at how these ampacity charts and tables can be used to ensure we select the appropriate conductor for the installation.
- First, we need to know what the conductor insulation is rated for since ampacity is a function of the temperature rating of the insulation.