NEC 225 for Apprentices: Feeding a Detached Garage or Second Building, Disconnects, Four-Wire Feeders and Grounding

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When Article 225 applies

Article 225 picks up whenever a branch circuit or feeder runs outside, on or between buildings and structures. The most common case for a residential apprentice is a subpanel in a detached garage, workshop or barn fed from the main panel in the house.

Question	Where to look
How many supplies the second building may have, and where its disconnect goes	Article 225, Part II
Overhead clearances and spans for outside conductors	Article 225, Part I
Burial depth for an underground feeder	Section 300.5 and Table 300.5
Equipment grounding conductor, electrodes and the neutral at the second building	Article 250
Sizing the feeder conductors and overcurrent protection	Articles 215, 240 and 310

One supply per building

A building or structure supplied by a feeder or branch circuit from another building generally gets only one feeder or branch circuit (NEC 225.30). The section lists special conditions where more are allowed, such as certain emergency or standby supplies and different characteristics like a different voltage. If a job calls for a second feeder to the same building, check that list before you plan it.

The disconnect at the second building

The building needs a disconnecting means for all ungrounded conductors that supply or pass through it (NEC 225.31). In general it must be readily accessible and located at the nearest point of entrance of the conductors, either inside or outside the building. In the 2026 NEC this location rule sits in the same section; older editions numbered it separately. The section has exceptions, for example for some buildings under single management with documented switching procedures, so check them before you depend on one.

The disconnect can be one device or a limited number of grouped devices (NEC 225.33), and it must be suitable for use as service equipment where the code requires it (NEC 225.36). Minimum ratings depend on what the building has, from a single small circuit up to a full panel (NEC 225.39). On many garage jobs the main breaker in the garage subpanel serves as this disconnect.

Four wires to the garage: keep the neutral off ground

For a new feeder to a second building, run an equipment grounding conductor with the feeder. For a typical 120/240 V single-phase garage panel serving both 120 V and 240 V loads, that means four conductors: two ungrounded conductors, the neutral and the equipment grounding conductor. A feeder serving only 240 V loads may not need a neutral.

At the second building:

• Neutral and ground stay separate. Land the neutral on an isolated neutral bar and the equipment grounding conductor on a ground bar bonded to the enclosure. Remove or do not install the bonding screw or strap in the subpanel.
• The building gets its own grounding electrode system. Connect the electrodes at the building, such as ground rods, to the equipment grounding bar with a grounding electrode conductor. The rules are in Article 250, Part III.
• Why it matters. If the neutral were bonded again at the garage, normal neutral current would split onto the grounding conductor, metal raceways and anything else bonded, so metal parts could carry current that should only flow on the neutral.

Older garages sometimes have a three-wire feeder with the neutral bonded at the garage. Article 250 still allows that only in existing installations that meet specific conditions. It is not how you wire a new feeder.

Worked example: 60 A feeder to a detached shop

A detached shop gets a 60 A, 120/240 V single-phase feeder from the house panel. Assume copper conductors, 75°C terminals at both ends, no correction or adjustment factors, and that the load calculation supports 60 A.

1. Ungrounded conductors. From the 75°C copper column of Table 310.16, 6 AWG is rated 65 A, which covers a 60 A breaker. 8 AWG is rated 50 A, which does not.
2. Neutral. Size it for the 120 V load it carries. Many installers simply run 6 AWG to match.
3. Equipment grounding conductor. Table 250.122 gives 10 AWG copper for a 60 A overcurrent device.
4. Conductor count. Four conductors: two hots, one neutral, one equipment grounding conductor.
5. At the shop. A panel with a main breaker as the building disconnect, the neutral bar isolated, the ground bar bonded to the can, and a grounding electrode conductor to the shop’s electrodes.
6. Check. 65 A is at least 60 A, so 6 AWG works. 10 AWG matches the 60 A row of Table 250.122.

If the feeder is long, check voltage drop as well. Our voltage drop calculator helps you compare conductor sizes.

Check yourself

1. How many feeders or branch circuits does a detached building generally get from another building? One, unless a listed special condition applies.
2. Where does the building disconnect generally go? At a readily accessible location nearest the point where the conductors enter, inside or outside.
3. In a new four-wire feeder to a garage, is the neutral bonded to the enclosure at the garage? No. Neutral and ground stay separate at the second building.

FAQ

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, Articles 225, 250 and 310