300.4 Protection from physical damage
What changed in 300.4
Under metal roof decking, a new concrete exception was added and the RMC/IMC exception now depends on the fittings. Protective fittings for 4 AWG and larger go on before the pull.
Point by point
- Under metal-corrugated roof decking, cables, raceways and boxes still need 1-1/2 inches of space below the deck, and no concealed wiring in that roof.
The full lesson is in the Pro Version
Get the whole breakdown
- 3 more points on exactly what changed
- The 2020 rule next to the 2023 rule, side by side
- Why it changed
- What to do and check on the job
One membership unlocks every NEC® change lesson for 2020, 2023 and 2026, plus every video, quiz, flashcard and the Testing Center.
Checking your membership…
This section across NEC® editions
2020 NEC®Revised
Where 4 AWG and larger conductors enter an enclosure from a raceway, a listed smooth-edged metal fitting now counts as protection, not just an insulating fitting.
Open the 2020 page →2023 NEC®RevisedYou're here
Under metal roof decking, a new concrete exception was added and the RMC/IMC exception now depends on the fittings. Protective fittings for 4 AWG and larger go on before the pull.
2026 NEC®Revised
Found at 300.6 in the 2026 NEC®.
The roof decking rule now covers every roof deck type and all wiring methods, and the bushing on 4 AWG and larger can go on after the pull.
Open the 2026 page →More 2023 changes in Article 300
This is a plain-English summary, not the NEC®'s exact wording. Always check the full section in the NEC® edition your area has adopted, plus any local amendments.
NEC® and National Electrical Code® are registered trademarks of the National Fire Protection Association (NFPA). Electrical Exam Coach is not affiliated with or endorsed by NFPA.
Find it faster on test day