3.5 Outside Branch Circuits, Feeders & Separate Buildings

Outside Branch Circuits, Feeders & Separate Buildings

Nebraska farmsteads, acreages, and commercial sites often supply a house, shop, machine shed, or grain bin from one service through outdoor feeders. Article 225 covers overhead and underground branch circuits and feeders run on or between buildings. Section 250.32 covers grounding and bonding at a building supplied by a feeder or branch circuit. Both topics fall under the "Wiring and Protection" area, the largest part of the PSI outline.

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1. Overhead Spans (225.6, 225.18, 225.19, 225.26)

Conductor size for overhead spans (225.6(A)), 1000 V or less:

• spans up to 50 feet: at least 10 AWG copper or 8 AWG aluminum;
• longer spans: at least 8 AWG copper or 6 AWG aluminum;
• unless the conductors are supported by a messenger wire.

Festoon lighting conductors must be at least 12 AWG unless supported by messenger wires.

Vertical clearance from ground (225.18). These match the service-drop values in 230.24(B):

The 18-foot value matters on farms. Fields, feedlots, and yard areas where trucks, combines, and grain carts travel count as land traversed by vehicles.

Clearances from buildings (225.19).

• Above roofs, keep 8 feet, with the same slope, overhang, and final-span exceptions as 230.24(A).
• Final spans must stay 3 feet from windows designed to be opened, doors, porches, balconies, ladders, stairs, and fire escapes. Conductors run above the top level of a window are exempt.

Vegetation (225.26). Trees and other vegetation may not support overhead conductor spans.

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2. Number of Supplies and Disconnects (225.30–225.39)

One supply per building (225.30). A building or structure supplied from the load side of a service disconnect may be supplied by only one feeder or branch circuit. Additional supplies are allowed only for the conditions in 225.30(A)–(E):

• special conditions such as fire pumps, emergency, legally required standby, optional standby, and parallel power production;
• special occupancies such as multi-occupancy buildings or very large buildings;
• capacity needs;
• different voltages, frequencies, or phases; and
• documented switching procedures.

Disconnecting means (225.31, 225.32).

• Each building needs a means to disconnect all ungrounded conductors that supply or pass through it.
• The disconnect must be readily accessible, either outside or inside nearest the point of entrance of the conductors.
• Exceptions apply to large buildings under single management with documented switching, and to some structures such as poles supporting luminaires.

Grouping and type (225.33–225.36).

• The disconnects for each supply are limited in number and must be grouped.
• Each building disconnect is a circuit breaker, molded-case switch, general-use switch, snap switch, or other approved means.
• Where the building's grounded conductor is bonded under the 250.32(B) exception for existing installations, the disconnect must be suitable for use as service equipment.

Minimum disconnect ratings (225.39):

Emergency disconnect for feeder-supplied dwellings (225.41, new in 2023). A one- or two-family dwelling supplied by an outdoor feeder needs an emergency disconnect. The rule mirrors 230.85 for services:

• it is installed in a readily accessible outdoor location on or within sight of the dwelling;
• its short-circuit current rating is at least the available fault current;
• multiple disconnects are grouped; and
• it is marked "EMERGENCY DISCONNECT."

A farmhouse fed from a yard pole is the classic example. Nebraska's statutory carve-out in § 81-2104(5) names 230.85, the service rule, and does not mention 225.41. Confirm with the state or local inspector how a feeder-supplied farmhouse will be inspected.

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3. Grounding and Bonding at a Separate Building (250.32)

Grounding electrode required (250.32(A)). Each building or structure supplied by a feeder or branch circuit needs a grounding electrode system built under Article 250, Part III, with a GEC to its disconnect. The exception: no electrode is required where the building is supplied by a single branch circuit (a multiwire branch circuit counts as one) that includes an EGC.

Bond through an EGC, not the neutral (250.32(B)(1)).

• Supply the building with an equipment grounding conductor run with the feeder or branch circuit, making a 4-wire feeder for 120/240 V.
• Connect the EGC to the building disconnect enclosure and to the building's grounding electrode(s).
• Do not connect the grounded (neutral) conductor to the EGC or to the electrode at the separate building. Keep the neutral bar isolated, exactly as in a subpanel.
• An exception lets existing installations that used a 3-wire feeder keep the neutral as the bond, but only if all three conditions hold:
  • no EGC was run with the supply;
  • no continuous metallic paths (water pipe, metal raceway, communication shields) connect the buildings; and
  • no ground-fault protection of equipment is installed on the supply side of the feeder.

GEC size (250.32(E)). Size the GEC per Table 250.66 based on the largest ungrounded supply conductor. The sole-connection limits of 250.66(A)–(C) still apply.

MAIN SERVICE (HOUSE)                 DETACHED SHOP (FEEDER)
Neutral bonded to enclosure (MBJ)    Neutral bar ISOLATED from enclosure
        |  4-wire feeder: L1, L2, N, EGC  |
        +---------------------------------+--> EGC bar bonded to enclosure
                                               + new grounding electrode(s)
                                                 (GEC sized per Table 250.66)

Farm distribution points

When two or more farm buildings are supplied from a distribution point, Article 547 adds the site-isolating device and its grounding rules (547.41, covered in Chapter 7). The feeders to each building still follow Article 225 and 250.32.

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4. Worked Example: Detached Shop Feeder

A homeowner's detached shop is fed from the house panel with a 100-A, 120/240-V underground feeder of 3 AWG copper conductors in PVC.

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5. Common Exam Traps

• Bonding the neutral at the shop: With a 4-wire feeder, the neutral stays isolated at the separate building. A bonding screw there creates parallel neutral paths.
• No electrode because "there's an EGC": A feeder-supplied building still needs its own grounding electrode. Only a single branch circuit is exempt.
• Farm field clearance: Overhead feeders crossing land traversed by farm vehicles need 18 feet, not 12.
• Tree supports: Trees may never support overhead spans.