Short answer: A feeder conductor must have an ampacity of at least the noncontinuous load plus 125% of the continuous load (NEC 215.4(A)(1)). After temperature correction and bundling adjustment, it must still carry the actual load (NEC 215.4(A)(2)). The feeder breaker or fuse is sized the same way, noncontinuous plus 125% of continuous, then the next standard rating (NEC 215.5). In the 2026 NEC these rules moved: the old 215.2 is now 215.4, the old 215.3 is now 215.5, and the old common neutral rule in 215.4 is now 215.14.
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Tsai Electro is an independent learning site. Not affiliated with TDLR, PSI or NFPA. We explain the ideas in our own words and do not reproduce NEC text. Check every rule and table value in your own 2026 NEC, and follow your supervisor and the local inspector.
The 2026 section numbers
If your study guide was written for an earlier edition, the numbers will not match. In the 2026 NEC, Article 215 goes from 215.1 straight to 215.4.
| Rule | Older editions | 2026 NEC |
|---|---|---|
| Minimum feeder conductor size | 215.2(A)(1) | 215.4(A)(1) |
| Feeder overcurrent protection | 215.3 | 215.5 |
| Common neutral for several feeders | 215.4 | 215.14(A) |
| Feeder and service load calculations | Article 220 | Article 120 |
Calculation 1: minimum feeder conductor
Noncontinuous load plus 125% of the continuous load, a load expected to run 3 hours or more.
Worked example. A feeder carries 40 A noncontinuous and 90 A continuous, with 75°C terminals.
- 125% of continuous: 1.25 × 90 = 112.5 A.
- Add noncontinuous: 112.5 + 40 = 152.5 A.
- In Table 310.16, 75°C copper column, the smallest conductor at or above 152.5 A is 2/0 copper (175 A).
Calculation 2: the correction and adjustment check
The first check uses the 125% figure against the ampacity at the terminal temperature rating, usually the 75°C column. The second check starts from the insulation temperature column, such as 90°C, and applies correction for ambient temperature and adjustment for more than three current-carrying conductors. After that, the conductor must still carry the load itself (NEC 215.4(A)(2)). Pass both.
Worked example. A feeder carries 140 A continuous and 20 A noncontinuous, with 75°C terminals. The conductors are 90°C copper. The correction factor is 0.87 and the adjustment factor is 0.80.
- First check: 1.25 × 140 + 20 = 195 A. 3/0 copper at 75°C is 200 A, so 3/0 passes.
- Second check, the load is 140 + 20 = 160 A. Start from the 90°C column: 3/0 is 225 A. 225 × 0.87 × 0.80 = 156.6 A, which is less than 160 A. 3/0 fails.
- Try 4/0: 260 × 0.87 × 0.80 = 181 A. 4/0 passes both checks.
Calculation 3: the feeder breaker
The breaker or fuse rating is not less than the noncontinuous load plus 125% of the continuous load (NEC 215.5).
Worked example. 210 A noncontinuous and 140 A continuous.
- 1.25 × 140 = 175 A.
- 175 + 210 = 385 A.
- The calculated minimum is 385 A. That is not a standard rating, so with standard-rated equipment the next standard size is 400 A.
100% rated equipment. Where the assembly, including the overcurrent device, is listed for operation at 100% of its rating, the device can be sized at the plain sum of continuous and noncontinuous load (NEC 215.5 Exception). With 320 A continuous and 50 A noncontinuous, that is 370 A, and the next standard rating is 400 A.
The feeder neutral
- Neutral not connected to an overcurrent device. Exception No. 3 to 215.4(A)(1) allows a grounded conductor that does not connect to an overcurrent device to be sized at 100% of the continuous and noncontinuous load (NEC 215.4(A)(1) Exception No. 3). With a 100 A continuous load, the phase conductors need 125 A, which is 1 AWG copper at 130 A. If the neutral carries the full 100 A in this simple example, it needs 100 A, which is 3 AWG copper in the 75°C column. On a real job, use the calculated neutral load and the other grounded conductor rules.
- Minimum neutral size. A feeder grounded conductor is never smaller than the EGC that Table 250.122 requires for that feeder (NEC 215.4(B)).
- Common neutral. One neutral may serve up to three sets of 3-wire feeders or two sets of 4-wire or 5-wire feeders (NEC 215.14(A)).
Voltage drop is a recommendation
The familiar figures, 3% for a feeder and 5% for feeder and branch circuit combined, are in an informational note under 215.4(A)(2) (NEC 215.4(A)(2) Informational Note No. 2). Informational notes are not requirements. On a 240 V feeder with a 7.84 V drop, the drop is 7.84 ÷ 240 = 3.27%, over the recommendation but not a code violation by itself. The job specification or a local rule can still require it.
Check yourself
- A feeder carries 60 A continuous and 30 A noncontinuous. What is the minimum ampacity? 1.25 × 60 + 30 = 105 A.
- Where is feeder overcurrent protection in the 2026 NEC? 215.5.
- Is the 3% feeder voltage drop figure mandatory? No. It is an informational note.
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Mark the 2026 feeder sections before exam day
NFPA 70, National Electrical Code, 2026 Edition (softcover). Write the old section numbers in the margin next to 215.4, 215.5 and 215.14, and highlight Exception No. 3 for the neutral. The Texas exam is open book. PSI allows a soft-bound NEC with highlighting, underlining and notes made in advance. Loose-leaf, spiral-bound and ring-bound copies are not allowed, and only permanent index tabs made or supplied by the NEC publisher are permitted; homemade and third-party tabs are not.
FAQ
How do you size a feeder conductor?
Use at least the noncontinuous load plus 125% of the continuous load, then check that the conductor still carries the load after temperature correction and bundling adjustment.
How do you size a feeder breaker?
With standard-rated equipment, the rating is at least the noncontinuous load plus 125% of the continuous load. If that is not a standard size, use the next standard rating. Equipment listed for 100% operation can use the 215.5 exception.
Where did 215.2 and 215.3 go in the 2026 NEC?
The minimum conductor rule is now 215.4(A)(1) and feeder overcurrent protection is now 215.5.
Can the feeder neutral be smaller than the phase conductors?
Yes, in some cases. Under Exception No. 3 to 215.4(A)(1), a neutral that does not connect to an overcurrent device can be sized at 100% of the load instead of 125% of the continuous load. It must still carry the calculated neutral load and must not be smaller than the EGC required by Table 250.122.
Are feeders on the Texas Journeyman exam?
PSI lists Feeders with 3 scored NEC Knowledge questions and 3 scored Calculations questions.
Sources checked October 2026
- PSI Candidate Information Bulletin, Texas electrician examinations (updated September 15, 2026): https://test-takers.psiexams.com/api/content/bulletin/1682
- NFPA 70, National Electrical Code, 2026 Edition, 215.4, 215.5, 215.14, 250.122 and Table 310.16
