6.5 Feeders and Outside Branch Circuits — Articles 215 and 225
Key Takeaways
- NEC 215.2(A)(1) requires feeder conductors to have an ampacity not less than the noncontinuous load plus 125 percent of the continuous load, and not less than the calculated load per Article 220.
- NEC 215.10 requires ground-fault protection of equipment for each feeder disconnect rated 1000 amperes or more on solidly grounded wye systems of more than 150 volts to ground but not exceeding 1000 volts phase-to-phase.
- NEC 215.6 requires a feeder supplying branch circuits with equipment grounding conductors to include or provide an equipment grounding conductor to which the branch-circuit equipment grounding conductors are connected.
- NEC 225.18 sets overhead conductor clearances of 10 feet, 12 feet, 15 feet, and 18 feet depending on voltage and what is below, mirroring the service clearances of 230.24(B).
- NEC 225.31 and 225.32 require a disconnecting means for all ungrounded conductors supplying a building or structure, installed at a readily accessible location either outside or inside nearest the point of entrance.
Feeder Minimum Rating and Size — 215.2
215.2(A)(1)(a) General. Feeder conductors shall have an ampacity not less than required to supply the load as calculated in Parts III, IV, and V of Article 220. The minimum feeder-circuit conductor size shall have an allowable ampacity not less than the noncontinuous load plus 125 percent of the continuous load.
Exception No. 1 applies where the assembly including the overcurrent devices is listed for operation at 100 percent of its rating. Exception No. 2 covers grounded conductors not connected to an overcurrent device.
215.2(A)(1)(b) Feeders Supplying Motor Loads. Sized per 430.24, 430.25, and 430.26 — covered in Chapter 10 of this guide.
215.2(A)(2) Ampacity Relative to Service Conductors. The feeder conductor ampacity shall not be less than that of the service conductors where the feeder conductors carry the total load supplied by service conductors with an ampacity of 55 amperes or less.
The Informational Note to 215.2(A) contains the feeder voltage-drop recommendation: conductors sized to prevent a voltage drop exceeding 3 percent at the farthest outlet, with the total on feeders and branch circuits not exceeding 5 percent, provide reasonable efficiency of operation. As with 210.19(A), this is a recommendation, not a mandatory rule.
Feeder Overcurrent Protection — 215.3
Feeders shall be protected against overcurrent in accordance with Part I of Article 240. Where a feeder supplies continuous loads or any combination of continuous and noncontinuous loads, the rating of the overcurrent device shall not be less than the noncontinuous load plus 125 percent of the continuous load, subject to the same 100-percent-rated-assembly exception.
Feeder Equipment Grounding — 215.6
Where a feeder supplies branch circuits in which equipment grounding conductors are required, the feeder shall include or provide an equipment grounding conductor, in accordance with the provisions of 250.134, to which the equipment grounding conductors of the branch circuits shall be connected.
This is why a subpanel in a detached structure, or any subpanel at all, must be fed with a separate equipment grounding conductor and must have its neutral isolated from the enclosure. The neutral-to-ground bond exists only at the service or at a separately derived system — 250.142(B).
Ground-Fault Protection of Equipment for Feeders — 215.10
Each feeder disconnect rated 1000 amperes or more and installed on solidly grounded wye electrical systems of more than 150 volts to ground but not exceeding 1000 volts phase-to-phase shall be provided with ground-fault protection of equipment in accordance with 230.95.
The classic covered system is 480Y/277 V, which is 277 V to ground. A 208Y/120 V system is only 120 V to ground and is not covered regardless of ampere rating.
Three exceptions apply: where ground-fault protection is provided on the supply side of the feeder and on the load side of any transformer supplying the feeder; for fire pumps; and for feeders supplying continuous industrial processes where a non-orderly shutdown would introduce additional or increased hazards.
Feeder Identification — 215.12
215.12(A) Grounded Conductor. Identified per 200.6.
215.12(B) Equipment Grounding Conductor. Identified per 250.119.
215.12(C) Identification of Ungrounded Conductors. Where a building has feeders supplied from more than one nominal voltage system, each ungrounded conductor shall be identified by phase or line and system at all termination, connection, and splice points. The means of identification shall be documented in a manner readily available or permanently posted at each feeder panelboard or similar distribution equipment. 215.12(C)(2) requires the high leg of a 4-wire delta system to be identified per 110.15 by an orange outer finish or other effective means, and durably and permanently marked at each point of connection.
Outside Branch Circuits and Feeders — Article 225
Article 225 covers requirements for outside branch circuits and feeders run on or between buildings, structures, or poles on the premises, and electrical equipment and wiring for the supply of utilization equipment located on or attached to the outside of buildings.
Clearances — 225.18 and 225.19
225.18 Clearance for Overhead Conductors and Cables. Overhead spans of open conductors and open multiconductor cables of not over 1000 volts nominal shall have a clearance of not less than:
| Clearance | Applies over |
|---|---|
| 10 ft | Above finished grade, sidewalks, or from any platform or projection from which they might be reached, where the voltage does not exceed 150 volts to ground and the area is accessible to pedestrians only |
| 12 ft | Over residential property and driveways, and those commercial areas not subject to truck traffic, where the voltage does not exceed 300 volts to ground |
| 15 ft | For those areas listed in the 12-foot classification where the voltage exceeds 300 volts to ground |
| 18 ft | Over public streets, alleys, roads, parking areas subject to truck traffic, driveways on other than residential property, and other land such as cultivated, grazing, forest, and orchard |
| 24.5 ft | Over track rails of railroads |
225.19 Clearances from Buildings for Conductors of Not Over 1000 Volts, Nominal. (A) Above roofs — 8 feet, with the same style of reductions found in 230.24(A). (B) From nonbuilding or nonbridge structures — 3 feet. (C) Horizontal clearances — 3 feet. (D) Final spans — clearance from windows designed to be opened, doors, porches, balconies, ladders, stairs, fire escapes, and similar locations shall be not less than 3 feet.
Compare this with the service clearances in 230.24(B), which are the same set of numbers. The Code deliberately mirrors them; the difference is which article applies to the conductors in front of you.
Number of Supplies — 225.30
A building or other structure served shall be supplied by only one feeder or branch circuit unless permitted in 225.30(A) through (F). The permitted additional supplies cover special conditions (fire pumps, emergency systems, legally required standby, optional standby, parallel power production, systems designed for connection to multiple sources), special occupancies by special permission, capacity requirements where the capacity requirements are in excess of 2000 amperes, different characteristics such as different voltages or phases, and documented switching procedures in large industrial installations.
Disconnecting Means — 225.31 through 225.33
225.31 Disconnecting Means. Means shall be provided for disconnecting all ungrounded conductors that supply or pass through the building or structure.
225.32 Location. The disconnecting means shall be installed either inside or outside of the building or structure served or where the conductors pass through the building or structure. The disconnecting means shall be at a readily accessible location nearest the point of entrance of the conductors. Exceptions cover installations under single management with documented safe switching procedures, garages and outbuildings on residential property where the disconnect is suitable for the conditions, and certain towers and poles.
225.33 Maximum Number of Disconnects. The disconnecting means for each supply permitted by 225.30 shall consist of not more than six switches or six circuit breakers mounted in a single enclosure, in a group of separate enclosures, or in or on a switchboard or switchgear. There shall be no more than six disconnects per supply grouped in any one location.
Notice the difference from services: the 2020 NEC changed 230.71 to require essentially one service disconnect (with the two-to-six allowance requiring separate enclosures or compartments), while 225.33 still permits six disconnects in a single enclosure for a feeder supply to a building.
225.36 Type. The disconnecting means specified in 225.31 shall be suitable for use as service equipment. An exception permits an isolating switch for towers or poles used as lighting standards.
225.38 requires the disconnecting means to plainly indicate whether it is in the open or closed position, and 225.37 requires permanent plaques or directories where a building is supplied by more than one feeder, branch circuit, or service, denoting all other supplies and their locations.
Alaska Application: Detached Shops and Outbuildings
A very common Alaska project is feeding a detached shop, garage, or cabin from a main dwelling. The rules that converge on that job are:
- 225.30 — one feeder to the structure unless a listed exception applies;
- 225.31/225.32 — a readily accessible disconnect at the structure, nearest the point of entrance;
- 225.36 — that disconnect must be suitable for use as service equipment;
- 250.32(A) — a grounding electrode system is required at the separate structure;
- 250.32(B)(1) — the feeder must include an equipment grounding conductor, and the grounded conductor must not be bonded to the enclosure at the outbuilding;
- 300.5 and Table 300.5(A) — burial cover for the underground run;
- 300.5(J) — arrangement to prevent damage from frost heave and settlement.
That last item is the one that separates a durable Alaska installation from a callback. Section 9.6 of this guide works through the grounding side in detail.
At what feeder disconnect rating does NEC 215.10 require ground-fault protection of equipment on a solidly grounded wye system of more than 150 volts to ground?
An overhead feeder span at 240 volts crosses a public street. What minimum clearance is required by NEC 225.18?
Under NEC 225.33, how many disconnecting means are permitted for each feeder supply to a separate building or structure?
What does NEC 225.36 require of the disconnecting means for a feeder supplying a detached garage?