You're right, the terminology surrounding ampacity adjustments for conductors has had a bit of a back-and-forth in the NEC. Here's a breakdown of why "derating" was replaced, and why it seems to be creeping back into the language

Why "Derating" Was Initially Phased Out:
Perceived Negativity

The term "derating" had a negative connotation. It implied that the conductor was somehow being made worse. It didn't accurately reflect that the ampacity was being adjusted to maintain safety under specific installation conditions.

Accuracy

The NEC uses adjustment and correction factors. Adjustment factors address conductor bundling and fill in a raceway, while correction factors address ambient temperature. Since "derating" was a general term and not specific to the adjustments, "adjust" and "correct" were determined to be more accurate.

Why "Derating" Seems to Be Reappearing (and Why It's Not a Complete Return)



Industry Understanding/Convenience

Despite the NEC's efforts to move away from "derating," the term remained widely used and understood in the electrical industry. It was, and still is, a convenient shorthand for the process of reducing a conductor's ampacity based on application.

Handbook Usage vs. Code Language

It's important to note the difference between the NEC code itself and the NEC Handbook. The Handbook is an interpretive guide. It is published by the same people that write the code (NFPA) but it is not enforceable. The Handbook can use language that resonates with electrical professionals, even if that language isn't strictly mirrored in the code. The goal of the handbook is to help electricians understand and apply the code.

Contextual Usage

The term "derating" in handbooks is often used as a more casual, general term to describe applying adjustment or correction factors. The code itself still uses the terms "adjust" and "correct" (or "adjustment factors" and "correction factors") when specifying the actual rules for ampacity modification.

In Summary

The NEC's official language still centers around "adjustment factors" and "correction factors" as the proper terms for modifying conductor ampacity. The term "derating" is primarily used informally or in explanatory contexts (like the Handbook) to refer to the overall process of applying these factors. Think of it like a legacy term, not officially sanctioned but still in common parlance. The key is to understand the rules in the NEC for adjustment and correction, regardless of what you call the process.

Important Note: Always refer to the latest edition of the NEC (and any local amendments) for the most current and accurate information. Never rely solely on memory or general industry terms when making electrical installations. Flag for review