5.2 Feeder Requirements (Article 215)

Why Feeders Matter

A feeder is any conductor between the service equipment and a final branch-circuit overcurrent device. In commercial work, feeders are the backbone of the distribution system. The Virginia exam will ask you to size feeder conductors, identify when ground-fault protection applies, and distinguish feeder taps from branch-circuit taps.

Feeder Conductor Ampacity (215.2)

215.2(A) requires feeder conductors to have an ampacity not less than the larger of two calculations:

1. (1) Before correction/adjustment: 125% of continuous load + 100% of noncontinuous load, based on the equipment temperature rating per 110.14(C)(1) and Table 310.16.
2. (2) After correction/adjustment: 100% of the total load after applying Table 310.15(B)(1)(1) ambient correction and Table 310.15(C)(1) adjustment factors.

The neutral conductor per 215.2(A)(2) must carry the maximum unbalanced load per 220.61 and not be smaller than required by 250.122 for the equipment grounding conductor.

Worked Example: Sizing a Feeder with Continuous Load

A feeder supplies a 100 A continuous load and a 100 A noncontinuous load at 75 °C terminals. The feeder ampacity before correction is (100 A × 1.25) + 100 A = 225 A. Using the 75 °C column of Table 310.16, 4/0 AWG copper at 230 A is the smallest conductor that satisfies 215.2(A)(1).

If the same load were supplied at 90 °C terminals with 75 °C equipment terminations, you would still use the 75 °C column for sizing because 110.14(C)(1) limits conductor ampacity to the equipment temperature rating unless all terminations are rated higher.

Feeder Overcurrent Protection (215.3)

Feeder OCPDs must be rated not less than 125% of the continuous load plus 100% of the noncontinuous load. An exception permits assemblies listed for 100% continuous duty, in which case the OCPD can be sized at 100% of the total load.

Equipment Grounding Conductor (215.6)

215.6 requires each feeder to include an equipment grounding conductor (EGC) sized per Table 250.122 based on the feeder OCPD rating. The EGC must be identified per 200.6; 6 AWG and smaller require green or green-with-yellow-stripe insulation, while 4 AWG and larger may be re-identified with green marking at terminations.

Feeder Tap Rules

In NEC 2020, the tap rules for feeders are located in 240.21(B), not 215.6. Section 215.15 requires barriers where feeder taps or transformer secondary conductors terminate so no energized bus is exposed when the OCPD is open. Common tap rules:

The next-size-up rule 240.4(B) does not apply to tap conductors.

Common Neutral (215.7)

215.7 permits a common neutral conductor for multiple feeders where the circuits are 3-wire or 4-wire wye systems, provided the neutral is sized to carry the maximum unbalanced load and the conditions of 215.7 are met. In practice, common neutrals are common in 3-phase 4-wire wye distribution but require careful load balancing to avoid harmonic heating.

Ground-Fault Protection of Equipment (215.10)

215.10 requires ground-fault protection of equipment (GFPE) at each feeder disconnect rated 1000 A or more supplied by a 4-wire, 3-phase, 277/480 V wye-connected system. The GFPE must comply with 230.95 and 240.13.

Three exceptions:

• Exception 1: Continuity of power required for life safety or chemical processes where hazard is documented.
• Exception 2: GFPE provided on the service side per 230.95 (service-level protection counts).
• Exception 3 (2020 addition): Temporary generator feeder conductors for repair/maintenance, limited to 90 days.

Exam Traps

• 215.2 vs 215.3: 215.2 sizes the conductor; 215.3 sizes the OCPD. They have the same 125% continuous-load formula but apply to different components.
• 215.6 is EGC, not taps: The exam may ask which article governs feeder tap rules; the answer is 240.21(B), not 215.6.
• 215.10 threshold: The trigger is 1000 A at the feeder disconnect, on 277/480 V wye. A 800 A feeder on the same system does not require GFPE.
• Temperature column: Always use the 75 °C column of Table 310.16 unless the equipment is marked for 90 °C terminations (rare) or 60 °C (older equipment).
• Next-size-up: 240.4(B) permits rounding up to the next standard OCPD when the conductor ampacity does not correspond to a standard size, but only for conductors 800 A and below, and never for tap conductors.

Worked Scenario: Commercial Feeder Sizing

A 277/480 V 3-phase 4-wire feeder supplies a panelboard with 180 A continuous load and 120 A noncontinuous load. Terminals are 75 °C. Size the conductor and OCPD.

Step 1 — Conductor ampacity (215.2). (180 A × 1.25) + 120 A = 225 + 120 = 345 A.

Step 2 — Table 310.16 (75 °C copper). 500 kcmil copper = 380 A. The next smaller size is 400 kcmil at 335 A (too small). So 500 kcmil Cu is required.

Step 3 — OCPD (215.3). Same 345 A calculation; next standard size above 345 A is 350 A (per 240.6). 500 kcmil Cu at 380 A supports a 350 A OCPD.

Step 4 — GFPE check (215.10). The feeder disconnect is 350 A, below the 1000 A threshold, so GFPE is not required.

Continuous vs Noncontinuous

A continuous load is one expected to operate at maximum current for 3 hours or more (Article 100 definition). Examples: lighting in retail, signage, data center cooling. The 125% factor ensures the conductor and OCPD are not loaded to nameplate continuously, preventing thermal damage.