Transformer overcurrent protection moved to 450.5
The transformer overcurrent protection rules and their two tables moved from 450.3 to 450.5. The percentages work the same way.
2023 vs. 2026
2023 NEC
450.3
Transformer overcurrent protection was in 450.3, with Table 450.3(A) for over 1000 V and Table 450.3(B) for 1000 V and less. Table 450.3(B) allowed 125%, 167%, or 300% on the primary alone, or 250% on the primary with 125% or 167% on the secondary.
2026 NEC
450.5
The same rules are in 450.5, with Table 450.5(A) and Table 450.5(B). 450.3 now covers reconditioned equipment.
What it means on the job
- Update the section on drawings, submittals, and calculation sheets.
- Exam candidates: look for transformer protection at 450.5.
Why it changed
To add: the code-making panel’s statement from NFPA’s public Second Draft Report, in our words, with a link to the source.
Section numbers only. Read 450.3 in the 2023 NEC and 450.5 in the 2026 NEC in your own code books, and check which edition your AHJ enforces.