Chapter 9 of the National Electrical Code (NEC) has changed greatly from what it was half a dozen Code cycles ago. Formerly, it contained complex tables for determining ampacity. That whole set of tables was simplified and moved to Chapter 3. The reason for that change was table usage was confusing and incorrect usage was a common cause of incorrect conductor sizing.
However, those weren’t the only tables in Chapter 9. It still has pages and pages of tables today. The first such table is, not surprisingly, Table 1. Table 1 applies only to conduit or tubing systems [Note 2].
This table consists of two columns and three rows. Simple to use, right? The title is your first clue that it may not always be simple to apply: “Percent of Cross Section of Conduit and Tubing for Conductors and Cables.” Your next clue is that it’s followed by two Information Notes and 10 Notes to Tables. While that plural form of Table might seem like a mistake, these notes don’t all apply to Table 1 (some notes explicitly refer to specific other tables).
