Somewhere between the service entrance and the branch circuits that actually power outlets, lights, and equipment, most buildings of any real size have at least one feeder -- a set of conductors that carries power from the service equipment (or another distribution point) to a panelboard, switchboard, or other distribution equipment downstream, without directly supplying any outlet or load itself. Feeders are the connective tissue of an electrical distribution system, and Article 215 is the article that governs how they're sized and protected. This article walks through what makes a feeder a feeder (as opposed to a branch circuit or a service conductor), the core sizing rule, overcurrent protection, voltage drop guidance, and five worked examples.
What Makes a Feeder a Feeder
The NEC defines three distinct categories of conductors as current flows from the utility toward an actual load, and knowing which category a given run of conductors falls into determines which article governs it:
- Service conductors — the run that brings power in from the utility and ends at the building's service disconnecting means, governed primarily by Article 230.
- Feeders — everything downstream of that: the conductors carrying power onward from service equipment (or from another feeder, when one feeder supplies a second one further down the line) toward the panelboard or distribution equipment where branch circuits ultimately originate, governed by Article 215.
- Branch circuits — the last leg of the journey, running from wherever a circuit picks up its own dedicated overcurrent device out to the actual outlet or load it powers, governed by Article 210 and covered in depth in our companion article.
A simple way to picture the chain: utility → service conductors → service equipment → feeder → subpanel → branch circuit → outlet/load. Not every installation has a feeder in this chain at all -- a small building with a single panel fed directly from service equipment has no feeder, just service conductors feeding branch circuits directly. Feeders become necessary once a building's distribution needs a subpanel, a separate structure, or additional distribution equipment downstream of the main service.
The Core Sizing Rule: 125% of Continuous Load
Take the feeder's noncontinuous load at face value, add 125% of its continuous load on top of that, and that combined figure is the minimum ampacity/rating the feeder conductors and their overcurrent device need to meet -- unless the whole assembly (conductors, overcurrent device, and terminations) carries a listing specifically for 100%-rated continuous duty. This is the exact same underlying logic used for branch-circuit sizing under Article 210 — a continuous load (trade shorthand for a load whose maximum current keeps running for three hours or longer) generates sustained heat that standard equipment isn't rated to handle at its full nameplate rating indefinitely, so an extra 25% margin is built in specifically for the continuous portion of the load. If you want the full derivation of why this 125% figure exists, see our companion article on branch circuits (NEC 210), which covers the identical concept in depth.
The calculation, spelled out as a formula: minimum feeder ampacity = (noncontinuous load × 100%) + (continuous load × 125%). Note that this 125% factor gets applied to the continuous portion of the load specifically -- not to the entire calculated feeder load indiscriminately -- so correctly separating continuous from noncontinuous loads before doing the math matters.
Feeder Load Calculations Come From Article 220
Article 215 governs how the feeder itself is sized and protected once you know the load it has to carry, but the actual calculated load value -- general lighting, small appliance and laundry circuits, demand factors, fixed appliances, and so on -- comes from the load calculation procedures in Article 220. This is why feeders and load calculations are such a natural companion topic: Article 220 tells you the number, and Article 215 tells you what to do with that number once you have it. See our companion article on load calculations (NEC 220) for the full walkthrough of how that calculated load figure gets built up in the first place.
Feeder Overcurrent Protection
Feeder conductors must be protected against overcurrent in accordance with their ampacity, following the same general overcurrent protection principles covered in Article 240 — the feeder's overcurrent device (typically a breaker or fuse at the source end of the feeder, such as at the main service panel or a switchboard) must not exceed the feeder conductors' ampacity, subject to the same standard-size rounding-up allowances used elsewhere in the code when the calculated ampacity doesn't correspond exactly to a standard overcurrent device size. Our companion article on overcurrent protection (NEC 240) covers those standard-size rounding rules in detail.
Feeder Voltage Drop — A Recommendation, Not (Generally) a Hard Rule
The NEC includes voltage drop guidance in an informational note recommending combined voltage drop on the feeder and branch circuit together be kept to a reasonable maximum (commonly cited as around 5% total, with roughly 3% recommended on the feeder alone and roughly 3% on the branch circuit, arranged so the combined total stays around 5%). This guidance is presented as a recommendation for efficient, reliable operation rather than a mandatory numeric limit in most general applications, though specific occupancies, local amendments, or engineering specifications can and do turn it into an enforceable requirement in particular contexts. Voltage drop matters for feeders specifically because feeders are often the longest conductor runs in a building, and a feeder run several hundred feet with an undersized conductor can produce a real, measurable voltage drop that affects equipment performance downstream, even when the conductor is otherwise correctly sized for ampacity. See our companion article on voltage drop calculations for the full worked-example walkthrough of this math.
Feeder Neutral Sizing
Unlike ungrounded (hot) feeder conductors, the neutral conductor of a feeder isn't automatically sized to match the ungrounded conductors -- it's sized based on the maximum unbalanced load the feeder is expected to carry, following the load calculation procedures in Article 220 for determining feeder neutral load, which commonly allows certain demand factors to reduce the calculated neutral load below the full connected load. This is why you'll sometimes see a feeder with a smaller neutral than its ungrounded conductors on a real job or exam question -- it isn't automatically an error, provided the neutral has been sized correctly based on the actual calculated unbalanced load rather than simply matched to the ungrounded conductor size out of habit.
Five Worked Examples
Example 1 — Basic Feeder Sizing With Mixed Continuous and Noncontinuous Load
Problem: A feeder supplies a subpanel with a calculated noncontinuous load of 40A and a calculated continuous load of 30A (such as a continuously operating sign circuit and similar sustained loads grouped on that subpanel). What's the minimum feeder ampacity?
Step 1 — Noncontinuous portion: 40A × 100% = 40A
Step 2 — Continuous portion: 30A × 125% = 37.5A
Step 3 — Add together: 40A + 37.5A = 77.5A
Result: Minimum feeder ampacity is 77.5A. Select conductors with an ampacity at or above 77.5A (after any applicable temperature/conductor-count adjustments), and a standard overcurrent device size that doesn't exceed that ampacity, rounding up to the next standard size as permitted.
Example 2 — Sizing a Feeder for a Small Commercial Subpanel
Problem: A calculated feeder load (from an Article 220 load calculation) comes out to 95A total, all of it noncontinuous (a mix of receptacle and equipment loads without a significant continuous-duty component). What's the minimum feeder ampacity, and what standard overcurrent device size would typically apply?
Step 1: Since the entire load is noncontinuous, no 125% multiplier applies — minimum feeder ampacity is simply 95A.
Step 2: Select conductors rated at least 95A, and a standard overcurrent device sized appropriately — commonly the next standard size at or above the conductor's ampacity, such as 100A, following the same standard-size rounding logic used throughout Article 240.
Result: 95A minimum conductor ampacity, with a 100A standard overcurrent device being a typical, code-compliant pairing for this scenario.
Example 3 — Feeder Overcurrent Protection Can't Exceed Conductor Ampacity
Problem: A feeder's calculated minimum ampacity is 68A, but the electrician has 2 AWG copper THHN conductors on the truck (rated 115A in the 90°C column, but subject to a 75A cap from 75°C-rated equipment terminations at both ends). Can a 100A breaker be used simply because it's "close enough" to a standard size above the 68A calculated load?
Answer: No. The overcurrent device must not exceed the conductor's actual usable ampacity, which here is capped at 75A by the termination equipment, not the conductor's 68A calculated minimum requirement and not the wire's uncapped 90°C rating. A 100A breaker paired with conductors usable only to 75A would leave the conductors under-protected against a fault or sustained overload between 75A and 100A. The correct overcurrent device size here tops out at 75A (or the next standard size at or below that limit, per the standard-size rounding provisions), not 100A.
Example 4 — Feeder Neutral Sized Smaller Than the Ungrounded Conductors
Problem: A feeder's ungrounded conductors are sized for 100A based on the connected load calculation. The calculated maximum unbalanced neutral load, per the Article 220 feeder neutral procedure, comes out to 70A. Is it acceptable to size the neutral conductor for only 70A instead of matching the 100A ungrounded conductors?
Answer: Yes — the feeder neutral is sized based on its own calculated maximum unbalanced load, not automatically matched to the ungrounded conductor size. As long as the 70A figure was correctly derived using the applicable Article 220 procedure (including any permitted demand factors), a smaller neutral than the ungrounded conductors is a normal, expected, and code-compliant outcome, not an error to be corrected by oversizing the neutral to match.
Example 5 — Voltage Drop on a Long Feeder Run
Problem: A feeder run to a detached garage subpanel is 180 feet long, calculated at exactly the minimum ampacity required by the connected load with no additional margin. Should the electrician consider upsizing the conductors beyond the bare minimum ampacity requirement?
Answer: While ampacity is satisfied at the calculated minimum size, a 180-foot run is long enough that voltage drop becomes a real practical concern, even though the NEC's voltage drop guidance is generally advisory rather than a hard numeric limit in most applications. A conductor sized only to the bare ampacity minimum on a run this long could produce a voltage drop noticeably above the commonly recommended combined 5% guidance, leading to dim lighting, sluggish motor starting, or other equipment performance issues at the far end. Good practice on a run this length is to run the voltage drop calculation separately (see our companion voltage drop article) and upsize the conductors beyond the bare ampacity minimum if the calculated drop exceeds a reasonable target, even though doing so isn't always a strict numeric code violation if skipped.
Common Mistakes
Frequently Asked Questions
Does every electrical system have a feeder?
No — a simple system where service conductors feed a single panel directly, with no subpanels or additional distribution equipment downstream, has no feeder at all, just service conductors feeding branch circuits directly. Feeders become necessary once a building's distribution requires a subpanel, a separate structure, or additional distribution equipment beyond the main service panel.
Can a feeder supply another feeder?
Yes — in larger or multi-building systems, a feeder can supply a switchboard or distribution panel that in turn feeds additional feeders downstream before finally reaching branch-circuit panelboards. Each of those conductor runs between distribution points is still governed by Article 215 as a feeder, regardless of how many stages exist between the service and the final branch circuit.
Is the 125% continuous-load rule the same for feeders and branch circuits?
Yes — it's the identical underlying rule and rationale applied at both levels: a load expected to keep drawing its maximum current for three hours or longer gets a 125% multiplier for sizing conductors and overcurrent devices, unless the assembly is specifically listed for 100% continuous-duty operation.
Do I always need to run a full voltage drop calculation on every feeder?
It's not universally mandatory in every jurisdiction and application, since the NEC's voltage drop guidance is generally informational/advisory rather than an enforceable numeric limit in most general contexts. That said, it's good practice on longer runs, and some local amendments, engineering specifications, or specific occupancy requirements can make it a firm, enforceable requirement — always check local requirements for the specific installation.
Can a feeder overcurrent device be sized smaller than the feeder's calculated ampacity, to save on breaker cost?
The overcurrent device generally needs to be sized appropriately for the conductor's ampacity and to actually carry the calculated load reliably without nuisance tripping — deliberately undersizing it below what the calculated load requires isn't a legitimate cost-saving strategy and would create both a nuisance-tripping problem and, depending on the specifics, a code compliance issue.
Key Terms
- Feeder: The stretch of conductors that carries power onward from service equipment (or from an upstream feeder) toward the distribution equipment where branch circuits originate, governed by NEC Article 215.
- Continuous load: Trade shorthand for a load that keeps drawing its maximum current for three hours or longer at a stretch, which is what triggers the 125% sizing multiplier for feeders and branch circuits alike.
- Feeder neutral: The grounded (neutral) conductor of a feeder, sized based on its own calculated maximum unbalanced load per Article 220, not automatically matched to the ungrounded conductor size.
- Service conductors: The run bringing power in from the utility and ending at the building's service disconnecting means, governed by Article 230 — upstream of any feeder.
- Branch circuit: The final leg of conductors, running from a circuit's own dedicated overcurrent device out to the outlet or load it powers, governed by Article 210 — downstream of any feeder.
Feeders sit right in the middle of the distribution chain, which is why this topic connects so directly to the articles on either side of it. Continue building this part of your knowledge with our companion articles on load calculations (NEC 220), branch circuits (NEC 210), overcurrent protection (NEC 240), and voltage drop calculations. Then put it into practice with our commercial load calculations practice test or general NEC code questions practice test. You can also browse more topics in our NEC code category.
This article is a study aid meant to help you understand the concepts and practice the math behind NEC Article 215 feeder rules. It is not a substitute for the official NEC and any state or local amendments that apply in your jurisdiction. Always verify exact requirements against the current adopted code edition and your local authority having jurisdiction before performing real electrical work.