Code Change Summary: New code definition of “free air (as applied to conductors)”.

For many code cycles, the NEC^® has had many code sections and tables providing requirements for conductors in “free air” but has never defined what “free air” actually is. It's often a struggle to know which NEC^® table applies when determining the ampacity of a conductor based on how its installed.

Are conductors in a cable tray considered to be in “free air” and which ampacity table is used when a conductor is not in a raceway or cable but happens to be touching something that may reduce the airflow around the conductor?

It seems that the code making panel also struggled with the final language between the first and second draft of the 2020 NEC^®. Below is the first draft language:

Free Air (as applied to conductors). Open or ventilated environment that allows for air flow around an installed conductor with no other conductors closer than one cable diameter and no insulation or building materials in contact with the conductor insulation for more than 75 mm (3 in.) for every 3 m (10 ft) of conductor.

After additional public comments at the second draft meeting, the final language was decided on and modified as shown below.

Keep in mind that the definition specifically applies to “conductors” and does not apply to cable type wiring methods that contain individual conductors within the cable assembly.

Below is a preview of the NEC^®. See the actual NEC^® text at NFPA.ORG for the complete code section. Once there, click on their link to free access to the 2020 NEC^® edition of NFPA 70.