NEC Article 225: Outside Branch Circuits & Feeders Guide
Running power to a detached garage, outbuilding, or separate structure on the same property requires compliance with NEC Article 225. This guide covers every aspect of outside branch circuits and feeders — from overhead conductor clearances and underground wiring methods to disconnecting means requirements, the number of disconnects allowed per 225.33, and grounding at separate buildings.
In This Guide
NEC 225 Scope and Purpose
NEC Article 225 covers the installation requirements for outside branch circuits and feeders run on or between buildings, structures, or poles on the premises. It also covers equipment and disconnecting means located on the outside of buildings or on or in other structures.
The scope of Article 225 picks up where the service entrance ends. Once power enters the main building and is distributed through the service equipment, any circuits that leave the building and travel to another structure on the same property fall under the requirements of Article 225. This includes wiring to detached garages, barns, workshops, pool houses, sheds with electrical loads, and separate buildings on commercial or industrial campuses.
Key Distinction: Service vs. Feeder
Service Conductors (Article 230)
Run from the utility to the main service disconnect. Covered by NEC Article 230 service entrance requirements.
Outside Feeders (Article 225)
Run from the main building's service equipment to another building or structure on the same property. Subject to Article 225 rules.
Article 225 is organized into three main parts: Part I covers general requirements for all outside branch circuits and feeders; Part II covers buildings or other structures supplied by a feeder or branch circuit; and Part III addresses installations over 1000 volts. For most residential and commercial work, Parts I and II contain the critical requirements.
Related NEC Articles
- Article 230: Services — covers conductors from utility to service equipment
- Article 215: Feeders — general feeder requirements (Article 225 supplements these for outside runs)
- Article 300: Wiring Methods — general installation requirements
- Article 250: Grounding and Bonding — grounding at separate buildings
- Article 310: Conductors — ampacity and sizing requirements
Overhead Conductor Installation & Clearances
Overhead spans between buildings are one of the most common methods for running feeders to detached structures. NEC Article 225 establishes strict clearance requirements to protect people, vehicles, and property from contact with overhead conductors. These clearances mirror many of the requirements found in NEC Article 230 for service drops.
Minimum Clearances from Ground (225.18)
Section 225.18 specifies the minimum height of overhead spans of outside branch circuits and feeders above finished grade, sidewalks, platforms, or other surfaces from which they might be accessible. The clearances vary based on the voltage and the area below the conductors.
| Location / Condition | Minimum Clearance |
|---|---|
| Above finished grade, sidewalks, or platforms accessible to pedestrians only (not exceeding 150V to ground) | 10 feet |
| Above finished grade, sidewalks, or platforms accessible to pedestrians only (exceeding 150V to ground) | 12 feet |
| Over residential property and driveways, and those commercial areas not subject to truck traffic (not exceeding 300V to ground) | 12 feet |
| Over residential property and driveways (exceeding 300V to ground) | 15 feet |
| Over public streets, alleys, roads, parking areas subject to truck traffic, driveways on other than residential property, and other land traversed by vehicles such as cultivated, grazing, forest, and orchard | 18 feet |
Clearances from Buildings (225.19)
Section 225.19 requires that overhead conductors and cables maintain specific clearances from buildings and structures. These clearances protect building occupants and prevent accidental contact during normal activities near the building.
Above Roofs
- General rule: 8 feet above the roof surface
- Roof slope ≥ 4/12: May be reduced to 3 feet
- Not exceeding 300V, not more than 4 feet of conductor over overhang: May be reduced to 18 inches
- Where roof is not readily accessible: Reduced clearance applies
From Windows & Openings
- From windows that open: 3 feet minimum
- From doors, porches, fire escapes: 3 feet minimum
- Above windows that do not open: Conductors may be installed above if clearance from upper edge is maintained
- Measured from: Where the conductors can be reached
Conductor Support and Attachment (225.15 & 225.16)
Overhead conductors must be supported on appropriate insulators or messenger cables. The point of attachment to a building must not be less than 10 feet above finished grade. Where individual open conductors are used, they must have a separation of at least 6 inches between conductors. When using cables (such as Type SE, USE, or MC), the cable assembly must be suitable for outdoor use and supported per manufacturer requirements.
Practical Overhead Span Considerations
- Maximum span: While no specific maximum span is given, conductors must be able to withstand weather loads and maintain required clearances under all conditions including ice loading and wind
- Drip loops: Provide drip loops at each building attachment to prevent moisture intrusion at the point of entry
- Messenger wire: For longer spans, a messenger wire (steel cable) supports the conductors to prevent excessive sag
- Trees: Overhead spans must not be routed through trees; tree growth can damage conductors and create hazards
Underground Feeder Methods
Underground installation is often preferred over overhead wiring because it eliminates clearance issues, provides better protection from weather and physical damage, and results in a cleaner appearance. For details on underground wiring methods, burial depths, and conduit requirements, see our comprehensive underground wiring installation guide.
Minimum Cover Requirements
NEC Table 300.5 specifies the minimum burial depths for underground conductors and cables. The required depth depends on the wiring method and the voltage of the circuit. Here are the most common scenarios for outside feeders:
| Wiring Method | Under Buildings | Under Driveways | General (No Specific Designation) |
|---|---|---|---|
| Rigid Metal Conduit (RMC) | 0 in (in raceway) | 18 in | 6 in |
| Intermediate Metal Conduit (IMC) | 0 in (in raceway) | 18 in | 6 in |
| PVC Schedule 80 or Rigid Nonmetallic Conduit | 0 in (in raceway) | 18 in | 18 in |
| UF Cable (Direct Burial, 120V GFCI protected or 120V residential only) | 0 in (in raceway) | 18 in | 12 in |
| UF Cable or Direct Burial Cable (general, not exceeding 600V) | 0 in (in raceway) | 24 in | 24 in |
Common Underground Wiring Methods
PVC Conduit with THWN/THHN
Schedule 40 PVC conduit with individual THWN-2 conductors is the most common method for underground feeders to detached buildings. Schedule 80 is required where the conduit emerges from the ground and is exposed to physical damage.
Advantages: Cost-effective, easy to install, allows conductor upgrades by pulling new wire
Direct Burial Cable (UF or USE)
Type UF (underground feeder) cable can be directly buried without conduit, though it requires deeper burial depths. Type USE-2 cable is also suitable for direct burial and underground service entrance applications.
Advantages: No conduit required, single trench operation
When sizing underground feeder conductors, be sure to account for voltage drop calculations — long runs to detached buildings often require oversized conductors to keep voltage drop within acceptable limits. NEC 210.19(A) Informational Note No. 4 and 215.2(A)(3) Informational Note No. 2 recommend a maximum 3% voltage drop on branch circuits and 5% combined feeder and branch circuit drop. Refer to wire sizing and NEC ampacity tables for proper conductor selection.
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Disconnecting Means at Detached Buildings
NEC Section 225.31 is one of the most critical requirements in Article 225: every building or structure supplied by a feeder or branch circuit must have a disconnecting means installed at a readily accessible location either outside the building or structure, or inside nearest the point of entry of the conductors.
225.31 — Disconnecting Means Required
For each building or structure served, a means must be provided to disconnect all ungrounded conductors that supply the building. The disconnect must be installed at a readily accessible location nearest the point of entry of the conductors, either outside or inside the building.
Disconnect Location Requirements (225.32)
Section 225.32 requires the disconnecting means to be installed at a readily accessible location. While both interior and exterior locations are permitted, the preferred location is:
Outside the Building
The most common and preferred location. An exterior-rated disconnect switch or circuit breaker is mounted on the outside of the detached building, near where the feeder conductors enter. This allows first responders to de-energize the building without entering.
Inside, Nearest Point of Entry
If installed inside, the disconnect must be located nearest the point of entry of the conductors. The intent is to minimize the length of unprotected feeder conductors inside the building. A sub-panel with a main breaker satisfies this requirement when located at the point of entry. For more details, see our sub-panel installation guide.
Disconnect Rating and Type (225.36 & 225.38)
The disconnecting means must meet specific rating and type requirements:
- Ampere rating: Must be rated not less than the calculated load to be served, per 225.39
- Suitable as disconnect: Must be listed and identified as suitable for use as service equipment when the building is the only structure on the premises, or listed as a disconnect if additional buildings are present
- Simultaneous disconnect: Each disconnect must simultaneously disconnect all ungrounded conductors it controls
- Indicating: Must clearly indicate whether it is in the open (off) or closed (on) position
Common Disconnect Types for Detached Buildings
Fusible Disconnect Switch
NEMA 3R rated outdoor enclosure with fused disconnect. Provides both disconnecting means and overcurrent protection.
Non-Fusible Disconnect
Provides disconnecting means only. Overcurrent protection must be provided by the breaker at the main panel.
Sub-Panel with Main Breaker
A loadcenter with a main circuit breaker serves as both disconnect and distribution panel. Most common for garages and workshops.
Minimum Disconnect Rating (225.39)
Section 225.39 establishes minimum ampere ratings for the disconnect, regardless of the actual calculated load:
| Application | Minimum Disconnect Rating |
|---|---|
| One-circuit installations | 15 amperes |
| Two-circuit installations | 30 amperes |
| One-family dwelling (all loads) | 100 amperes |
| All other installations | 60 amperes |
Number of Disconnects Allowed (225.33)
NEC Section 225.33 addresses one of the most commonly referenced provisions of Article 225: the maximum number of disconnecting means permitted for each supply at a building or structure.
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.
This is commonly known as the “six disconnect rule” or the “six throw rule” — all power to the building must be disconnectable in no more than six motions of the hand.
In practice, most detached buildings use a single disconnect — either a standalone disconnect switch or a sub-panel with a main breaker. The six-disconnect option is more commonly encountered in commercial and industrial settings where multiple feeders serve different systems in the same building.
Compliant Examples
- ✓ Single 200A main breaker panel serving entire detached garage
- ✓ Three disconnect switches (lighting, HVAC, process) grouped together on an industrial outbuilding
- ✓ Six circuit breakers in a single switchboard serving all loads in a warehouse building
- ✓ One disconnect for each of two separate supplies to one building (two groups of up to six each)
Non-Compliant Examples
- ✗ Seven individual disconnect switches for one supply on a building
- ✗ Six disconnects scattered at different locations around the building (must be grouped)
- ✗ MLO (main-lug-only) panel with no separate disconnect at a detached building (no disconnect means at the building)
- ✗ A panelboard behind locked rooms counted as the disconnect (not readily accessible)
225.30 — Number of Supplies
Section 225.30 limits each building or structure to be supplied by only one feeder or one branch circuit, unless one of several exceptions is met. Exceptions include separate systems (fire pumps, emergency power, legally required standby), different voltages or frequencies, different uses, capacity requirements exceeding 2000 amperes, parallel power production systems, and documented switching procedures for multiple sources.
Grounding at Separate Buildings
Grounding requirements at separate buildings supplied by feeders are covered in NEC Section 250.32, which works in conjunction with Article 225. This is one of the most complex and commonly misunderstood areas of outside feeder installation. For a deep dive into grounding principles, see our NEC Article 250 grounding guide.
Grounding Electrode System Required (250.32(A))
A grounding electrode system must be established at each separate building or structure served by a feeder. This includes any electrodes present at the building (such as metal underground water pipe, concrete-encased electrodes, ground rods, or ground rings) and must comply with the requirements of NEC 250.50 through 250.60.
Grounding Electrode Conductor (GEC)
A grounding electrode conductor must be installed at the separate building to connect the equipment grounding bar to the grounding electrode system. The GEC is sized per NEC Table 250.66 based on the size of the feeder conductors.
| Feeder Conductor Size (Copper) | Minimum GEC Size (Copper) |
|---|---|
| #2 AWG or smaller | #8 AWG |
| #1 or 1/0 AWG | #6 AWG |
| 2/0 or 3/0 AWG | #4 AWG |
| Over 3/0 through 350 kcmil | #2 AWG |
Equipment Grounding Conductor (EGC) Method
Under the current NEC, the standard method for grounding at a separate building is to run an equipment grounding conductor (EGC) with the feeder conductors from the main building to the detached building. At the detached building:
- The neutral (grounded conductor) must be isolated from the equipment grounding system — the neutral bar must not be bonded to the enclosure
- A separate equipment grounding bar must be installed and bonded to the enclosure
- The EGC connects to the equipment grounding bar
- A grounding electrode conductor connects the equipment grounding bar to the local grounding electrode system
Critical: Neutral-Ground Bond Location
When an EGC is run with the feeder, the neutral must not be bonded to ground at the separate building. The neutral-ground bond exists only at the main service equipment (250.24(A)(5)). Bonding neutral to ground at both the main building and the detached building creates parallel return paths for neutral current through the grounding system, which can cause dangerous voltages on metal equipment, objectionable current flow on metal piping, and interference with ground-fault protection devices.
Existing Installations — Legacy Exception
In older installations, you may encounter feeders to detached buildings that use the neutral conductor for both the neutral return and the equipment grounding path (a three-wire feeder with no separate EGC). This was permitted under older editions of the NEC but is no longer allowed for new installations. Existing installations are typically grandfathered, but any new feeders or replacement feeders must include a separate EGC and maintain neutral-ground isolation at the detached building. For more on grounding and bonding, see our grounding vs. bonding guide.
Multi-Building Campuses
Commercial and industrial properties with multiple buildings present unique challenges for outside feeder design. Article 225 applies to each building or structure individually, meaning each building must have its own disconnecting means, grounding electrode system, and compliant feeder installation.
Campus Distribution Considerations
- Single supply per building: Each building generally receives one feeder per 225.30 (exceptions apply)
- Disconnect at each building: Every building must have its own disconnect per 225.31
- Feeder sizing: Size each feeder for its building's calculated load plus any applicable demand factors
- Voltage drop: Longer runs between buildings require careful voltage drop analysis
- Coordination: Overcurrent devices must be coordinated for selective tripping
Common Campus Wiring Methods
- Underground duct bank: Multiple conduits in a common trench, often with concrete encasement for protection
- Direct buried cables: Suitable for less congested routes with proper marking tape
- Overhead pole line: Used where underground is impractical or too expensive
- Medium voltage distribution: Campuses over a few hundred feet often use 4160V or higher distribution with step-down transformers at each building
- Pad-mounted transformers: Common for converting medium voltage distribution to utilization voltage at each building
Feeder Sizing for Detached Buildings
Size outside feeders per NEC Article 220 load calculations, just as you would for any feeder. Key considerations for outside feeders include:
- 225.39 minimums: Disconnect rating must meet the minimums regardless of calculated load
- Conductor ampacity: Per NEC 310 and applicable ampacity tables, accounting for temperature correction and adjustment factors
- Voltage drop: Calculate voltage drop for the feeder length and increase conductor size as needed
- Future load growth: Consider oversizing feeders and conduits for anticipated future loads
- Environmental conditions: Apply derating for underground installations in high-temperature soil or for conduits with multiple circuits
Common Code Violations
Outside feeders and branch circuits to detached buildings are frequently cited during electrical inspections. Understanding the most common violations helps you avoid them and pass inspection the first time.
No Disconnect at Detached Building
Running a feeder to a sub-panel in a detached garage without providing a disconnect at or near the building. An MLO (main lug only) panel alone does not satisfy the disconnecting means requirement unless there is a separate disconnect switch.
Neutral Bonded to Ground at Sub-Panel
Bonding the neutral bar to the enclosure at the detached building sub-panel when a separate EGC is run with the feeder. The neutral must be isolated at the sub-panel; only the EGC bar bonds to the enclosure.
Insufficient Overhead Clearance
Overhead conductors that sag below the required minimum clearance heights, especially over driveways (12 feet minimum for residential, 300V or less) or areas accessible to pedestrians (10 feet for 150V or less).
Inadequate Burial Depth
Underground feeder cables or conduits buried at insufficient depth. Common mistake: burying UF cable at 12 inches under a driveway when 24 inches (or 18 inches for conduit) is required.
No Grounding Electrode at Detached Building
Failing to install a grounding electrode system at the separate building. At minimum, two ground rods spaced 6 feet apart are typically required (or a single rod if tested at 25 ohms or less).
Missing EGC with Feeder
Running only three wires (two hots and a neutral) to a detached building without an equipment grounding conductor. Current NEC requires a four-wire feeder (two hots, neutral, and EGC) for new installations.
Disconnect Not Readily Accessible
Placing the disconnect behind locked doors, above suspended ceilings, or in locations that require a ladder or removal of obstacles to reach. “Readily accessible” means capable of being reached quickly without climbing, removing obstacles, or using keys.
Undersized Conductors (Voltage Drop)
Using conductors sized only for ampacity without accounting for voltage drop on long runs. A 200-foot underground run to a detached garage may need conductors two or three sizes larger than the minimum ampacity rating requires.
Pre-Inspection Checklist
- ☐ Disconnect installed at detached building per 225.31/225.32
- ☐ Disconnect rated per 225.39 minimums
- ☐ No more than six disconnects per supply per 225.33
- ☐ Overhead clearances meet 225.18/225.19 requirements
- ☐ Underground burial depths meet Table 300.5
- ☐ EGC run with feeder conductors
- ☐ Neutral isolated from ground at sub-panel (not bonded)
- ☐ Grounding electrode system installed at detached building
- ☐ GEC sized per Table 250.66
- ☐ Conductors sized for both ampacity and voltage drop
- ☐ Physical protection provided where conductors emerge from ground
Frequently Asked Questions
Do I need a disconnect at a detached garage?
Yes. NEC 225.31 requires a disconnecting means at every building or structure supplied by a feeder or branch circuit. For a detached garage, this is typically satisfied by either an exterior disconnect switch or a sub-panel with a main breaker located inside the garage near the point of conductor entry.
Can I use an MLO (main lug only) panel at a detached building?
You can use an MLO panel only if a separate disconnect is provided at the building. The MLO panel itself does not satisfy the disconnect requirement of 225.31. Common solutions include installing a disconnect switch ahead of the MLO panel, or simply using a panel with a main breaker instead.
What size wire do I need to run to my detached garage?
The wire size depends on the load you plan to serve and the distance of the run. For a typical residential detached garage with a 60A sub-panel and a 100-foot run, #6 AWG copper or #4 AWG aluminum conductors are common starting points, but you must calculate the actual load and check voltage drop for your specific distance. Longer runs may require larger conductors.
Do I need ground rods at the detached building?
Yes. Per NEC 250.32(A), a grounding electrode system must be established at each separate building. In most cases, this means installing at least two ground rods (each at least 8 feet long) spaced a minimum of 6 feet apart. If the first ground rod has a resistance of 25 ohms or less, a single rod is acceptable, but most electricians install two as standard practice. A grounding electrode conductor must connect the electrode system to the equipment grounding bar in the sub-panel.
Can I run a 240V circuit to an outbuilding for a single piece of equipment?
Yes, you can run a single branch circuit (rather than a full feeder) to an outbuilding for a dedicated load. A disconnect is still required at the outbuilding per 225.31. The circuit must still comply with all applicable Article 225 requirements for overhead clearances or underground burial depth. The disconnect can be as simple as a single-pole switch or a listed disconnect switch rated for the circuit.
What is the minimum overhead clearance over a residential driveway?
For overhead conductors not exceeding 300 volts to ground (which covers most 120/240V residential feeders), the minimum clearance over residential driveways is 12 feet per NEC 225.18. For conductors exceeding 300V to ground, the minimum increases to 15 feet. Over areas subject to truck traffic, the requirement is 18 feet.
Should the neutral be bonded to ground at the detached building?
No — not when an equipment grounding conductor (EGC) is run with the feeder, which is required for all new installations. The neutral must be isolated at the detached building. The neutral-ground bond exists only at the main service equipment in the main building. Bonding neutral to ground at both locations creates hazardous parallel return paths for current.
How many feeders can supply one detached building?
Per NEC 225.30, each building or structure shall be supplied by only one feeder or one branch circuit unless specific exceptions apply. Exceptions include separate supplies for fire pumps, emergency systems, legally required standby systems, optional standby systems, parallel power production, and documented switching procedures. When multiple supplies are permitted, each supply can have up to six disconnects per 225.33.
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