338.10(B)(4) Installation Methods for Branch Circuits and Feeders.
Code Change Summary: Reorganized code language on the installation rules for SE cables used for branch circuits and feeders.
In this code cycle, the rules for SE cable installation methods have simply been reformatted into a list for clarity. The 2020 NEC® is the first in many code cycles where the rules were just restructured rather than completely changed altogether.
In the 2017 NEC®, a change occurred to require the ampacity of 10 AWG and smaller Type SE cables, installed in thermal insulation, to be based on the 60°C conductor temperature rating in the ampacity table. This change provides relief for 8 AWG and larger Type SE cables installed in thermal insulation.
The ampacity requirements for SE cables have changed almost every code cycle since the 1999 NEC®. When using SE cables for interior wiring, they consistently have been required to comply with the overall installation requirements of Nonmetallic-Sheathed cables but the ampacity requirements have gone back and forth each code cycle due to limitations placed on Nonmetallic-Sheathed cables in the 1980’s.
Nonmetallic-Sheathed cable (NM-B) ampacity was limited to the 60°C column in the ampacity table in the 1980’s because of overheating occurring in luminaires installed in ceilings after thermal insulation was blown in over the conductors and fixtures in the 1970’s. The trapped heat from the luminaires caused heat damage to the 60°C NM cable jacket. As a result, a code change in the 1984 NEC® required Nonmetallic-Sheathed cables to be constructed with 90°C insulation but limited the overall cable ampacity to the 60°C column of the ampacity table.
Nonmetallic-Sheathed cables are mostly used for small branch circuits and devices like switches and receptacles that are equipped with 60°C terminals (unless marked otherwise). SE cables are often used for feeders, or larger branch circuits in residential installations to supply appliances such as ranges, dryers and air conditioners. Most Type SE cables have 75°C or 90°C rated conductor insulation. Appliance receptacles sized 30 amps and larger typically have 75°C terminals. Therefore, the breaker, cable, and receptacles are all suitable for use at 75°C.
If SE cable was most commonly used for branch circuit light switches and receptacles, it would be understandable to limit SE cable ampacity to fall within the temperature limitations of the devices and luminaires. However, for larger conductor applications, there is no logical or technical reason to restrict the ampacity of a 75°C or 90°C rated SE cable to 60°C if the cable will be terminated to 75°C or 90°C rated terminals.
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.
2017 Code Language:
338.10(B)(4) Installation Methods for Branch Circuits and Feeders.
(a) Interior Installations. In addition to the provisions of this article, Type SE service-entrance cable used for interior wiring shall comply with the installation requirements of Part II of Article 334, excluding 334.80.
For Type SE cable with ungrounded conductor sizes 10 AWG and smaller, where installed in thermal insulation, the ampacity shall be in accordance with 60°C (140°F) conductor temperature rating. The maximum conductor temperature rating shall be permitted to be used for ampacity adjustment and correction purposes, if the final derated ampacity does not exceed that for a 60°C (140°F) rated conductor.
Informational Note No. 1: See 310.15(A)(3) for temperature limitation of conductors.
Informational Note No. 2: For the installation of main power feeder conductors in dwelling units refer to 310.15(B)(7).
(b) Exterior Installations. In addition to the provisions of this article, service-entrance cable used for feeders or branch circuits, where installed as exterior wiring, shall be installed in accordance with Part I of Article 225. The cable shall be supported in accordance with 334.30. Type USE cable installed as underground feeder and branch circuit cable shall comply with Part II of Article 340.
2020 Code Language:
338.10(B)(4) Installation Methods for Branch Circuits and Feeders.
Informational Note No. 1: See 310.14(A)(3) for temperature limitation of conductors.
Informational Note No. 2: For the installation of main power feeder conductors in dwelling units refer to 310.12.
(a) Interior Installations.
(1) In addition to the provisions of this article, Type SE service-entrance cable used for interior wiring shall comply with the installation requirements of Part II of Article 334, excluding 334.80.
(2) Where more than two Type SE cables containing two or more current-carrying conductors in each cable are installed in contact with thermal insulation, caulk, or sealing foam without maintaining spacing between cables, the ampacity of each conductor shall be adjusted in accordance with Table 310.15(C)(1).
(3) For Type SE cable with ungrounded conductor sizes 10 AWG and smaller, where installed in contact with thermal insulation, the ampacity shall be in accordance with 60°C (140°F) conductor temperature rating. The maximum conductor temperature rating shall be permitted to be used for ampacity adjustment and correction purposes, if the final ampacity does not exceed that for a 60°C (140°F) rated conductor.
(b) Exterior Installations.
(1) In addition to the provisions of this article, service-entrance cable used for feeders or branch circuits, where installed as exterior wiring, shall be installed in accordance with Part I of Article 225. The cable shall be supported in accordance with 334.30.
(2) Type USE cable installed as underground feeder and branch circuit cable shall comply with Part II of Article 340.