Code Applied by the app elec.conductor.ampacity
Conductor ampacity
The current a conductor may carry, read from the ampacity table in the column its terminals allow: #3/0 copper carries 200 A at 75 °C, which is why a 200 A feeder is #3/0.
| When | The app uses |
|---|---|
| #3/0 copper THHN, read in the 75 °C terminal column | 200 A |
- Source
- NEC · 310.16 (Table 310.15(B)(16) in 2017) · read the public text
- Editions checked
- 2017 · 2020 · 2023
- Used by
- Courses
- Amendments
No state or local amendment to this rule is on file. Not on file means the model code as written — check your jurisdiction.
A model code the authority having jurisdiction adopts.
Each wire size has an ampacity, the current it may carry continuously, and the table gives it in three temperature columns. The insulation may be rated for the hottest column, but the conductor is read in the column its terminals are rated for, which on most breakers and lugs is 75 °C. That is how the course reads the restaurant's feeder: a 200 A main wants a conductor good for 200 A, and #3/0 copper THHN is 200 A in the 75 °C column.
On a bid the feeder is the heaviest wire on the job and the most expensive by the foot, and its size decides the conduit (2 inches, for four #3/0 and a ground). Reading the wrong column moves the whole run a size.
What the app does with it
The electrical course teaches it on two cards (Chapter 1, Read a row, and Chapter 7, Read the one-line), and check-lesson-rules holds the cards' numbers to this rule. The app counts the feeder's wire from the conductors you write on its line type; it does not check the size against the load.
Verify against your edition
The table is 310.16 from the 2020 edition on; the 2017 edition numbers it Table 310.15(B)(16). The column the terminals allow comes from 110.14(C), and a hot ambient or more than three current-carrying conductors in one raceway derate the figure. On a 3-phase 4-wire wye the neutral counts as current-carrying when most of the load is nonlinear; the course's restaurant is mostly motors and heat, so its four #3/0 are not derated for it. Local amendments still govern.
Settled 2026-09-27 by Claude on the owner's delegation, from the dossier's research and the model code text; not checked against a printed book or a local amendment.
Cited by section, not reprinted: the code text belongs to its publisher. Company practice is not a rule here — it lives with your pricing.