Article 225 provides installation requirements for outside branch circuits and feeders that run on (or between) structures or poles (Fig. 1). The NEC differentiates between buildings and structures, but for convenience we'll refer to both of them as structures.
Other articles also pertain to outside branch circuits (see Other Articles Related to Outside Branch Circuits on page 71); most of these are application-specific. Lighting is the most common application. Make sure you don't place 277V luminaires within 3 feet of platforms, fire escapes, or windows that open [225.7(C)] (Fig. 2 on page 69). See 210.6(C) for the types of luminaires permitted on 277V or 480V branch circuits.
Festoon lighting is a string of outdoor lights suspended between two points [Art. 100]. It's commonly used at carnivals and similar functions [525.20(C)]. Festoon lighting conductors must be at least 12 AWG, unless messenger wires support them. Overhead festoon lighting conductors must be supported by messenger wire (with strain insulators) when spans exceed 40 feet [225.6(B)].
Conductor size and support
For overhead spans up to 50 feet, the minimum conductor size for outside branch circuits is 10 AWG. For longer spans, it's 8 AWG [225.6(A)].
When these spans are installed over a building, they must be securely supported by substantial structures [225.15]. Where practicable, supports must be independent of the building [230.29]. If you use a mast for support, it must have adequate mechanical strength, braces, or guy wires to withstand the strain caused by the conductors [225.17]. Don't use trees or other vegetation for conductor support [225.26].
The points of attachment for overhead conductors must be at least 10 feet above finished grade. Maintain the minimum conductor clearance required by 225.18, even if that means raising the points of attachment (Fig. 3 on page 70).
When attaching open conductors, use fittings identified for use with conductors. Alternatively, you can use noncombustible, nonabsorbent insulators securely attached to the structure. You can attach branch conductors to the service mast, but don't attach aerial communications cables or antennas to it [810.12].
For overhead conductors of 600V or less, maintain the following clearances: [225.18]:
10 feet above finished grade, sidewalks, platforms, or projections from which they might be accessible to pedestrians if circuits are 150V to ground or less. Article 225 doesn't provide a clearance for over 150V.
12 feet above residential property and driveways, and commercial areas not subject to truck traffic if circuits of 300V to ground or less. It's 15 feet for circuits over 300V to ground.
18 feet over public traffic ways, parking areas subject to truck traffic, driveways on other than residential property, and other areas traversed by vehicles (e.g., those used for cultivation, grazing, or forestry).
Observe the clearance requirements in 680.8 for any conductor that runs above pools, outdoor spas, outdoor hot tubs, diving structures, observation stands, towers, or platforms.
Conductors must maintain a vertical clearance of 8 feet above the surface of a roof, for least 3 feet from the edge of the roof. Four exceptions exist, and they're listed in 225.19(A).
Conductors must maintain a vertical, diagonal, and horizontal clearance of at least 3 feet from signs, chimneys, radio and television antennas, tanks, and other structures (buildings and bridges are excluded) [225.19(B)].
Final span clearance
Remember earlier we said you have to keep luminaires at least 3 feet from platforms and similar locations? The same thing applies to overhead conductors. But conductors that run above a window aren't required to maintain the 3 feet distance.
Conductors must maintain a vertical clearance of at least 10 feet above platforms, projections, or surfaces from which they might be reached. This vertical clearance must be maintained for 3 feet, measured horizontally from those surfaces.
Don't install conductors under an opening through which materials might pass, or where conductors will obstruct building openings [225.19(D)(3)] (Fig. 4 on page 70). Arrange raceways on exterior surfaces so they drain. In wet locations, they must be rain-tight [225.22].
Where more than one structure is on the same property, each must be served by no more than one feeder or branch circuit [225.30]. As you might expect, the NEC provides several exceptions.
The first one is “Special Conditions.” You can provide additional circuits for:
Legally required standby systems,
Optional standby systems,
Parallel power production systems, and
Systems designed for connection to multiple sources of supply for the purpose of enhanced reliability.
You can also, by special permission, provide additional feeders for:
Multiple-occupancy buildings where there's no available space for supply equipment accessible to all occupants.
A structure so large that two or more feeder supplies are necessary.
The three other exceptions are:
The capacity requirements exceed 2,000A.
Different voltages, frequencies, or uses. For example, control of outside lighting from multiple locations.
Documented safe switching procedures are established and maintained for disconnection.
Provide a disconnecting means for all conductors that enter a structure [225.31]. Install it at a readily accessible location nearest the point of entrance of the conductors [225.32]. You can locate it elsewhere:
Where documented safe switching procedures are established and maintained. But it must be monitored by qualified persons (see Art. 100).
A disconnecting means isn't required within sight of poles that support luminaires.
The disconnecting means for a sign doesn't need to be readily accessible if installed per the requirements for signs. Each sign must be controlled by an externally operable switch or circuit breaker that opens all ungrounded conductors to the sign. The sign disconnecting means must be within sight of the sign, or the disconnecting means must be capable of being locked in the open position [600.6(A)].
The structure disconnecting means can consist of no more than six switches (or circuit breakers) in a single enclosure, or separate enclosures for each supply permitted by 225.30. Group all disconnects in one location [225.34], and mark each one to indicate the loads served [110.22].
To minimize accidental interruption of the critical power systems, 225.30(A) requires the disconnecting means for a fire pump [695.4(B)(2)] or standby power [701.11(E)] to be located remotely from the normal power disconnect. First responders to a fire can shut down power to the facility without shutting off the fire pump.
In a multiple-occupancy building, each occupant must have access to the disconnecting means for the occupancy [225.35]. The occupant disconnect can be accessible to building management, if management provides electrical maintenance under continuous supervision.
You can use a snap switch (or a set of 3-way or 4-way snap switches) as the disconnecting means for garages and outbuildings on residential property without having a “service equipment” rating.
Where more than one feeder supplies a structure, a permanent plaque or directory must be installed at each feeder disconnect location and denote all other feeders supplying that structure and the area served by each [225.37].
The structure disconnecting means can consist of either a manually operated switch (or circuit breaker) or a power-operated one that's capable of being operated manually [225.38]. If you use a shunt-trip push button as the means of opening a power-operated circuit breaker, the breaker is the disconnecting means and the push button is not.
The feeder or branch-circuit disconnecting means for a structure must have an ampere rating not less than the calculated load determined per Art. 220 [225.39]. But observe the following:
- One-circuit installation
The disconnecting means must have a rating at least 15A.
- Two-circuit installation
The feeder disconnecting means must be rated at least 30A.
- One-family dwelling
The feeder disconnecting means must be rated at least 100A, 3-wire.
For all other installations, the feeder or branch-circuit disconnecting means must be rated at least 60A.
You may have noticed that Art. 225 is primarily concerned with clearances, support, and disconnects. If you address those issues before starting your outside branch-circuit installations, you should have no problem complying with Art. 225. Be sure to review Table 225.2 for other applicable Articles and comply accordingly.
Sidebar: Other Articles Related to Outside Branch Circuits
Branch circuits (Art. 210)
Class 1, Class 2, and Class 3 remote control, signaling, and power-limited circuits (Art. 725)
Communications circuits (Art. 800)
Community antenna television and radio distribution systems (Art. 820)
Conductors for general wiring (Art. 310)
Electric signs and outline lighting (Art. 600)
Feeders (Art. 215)
Floating buildings (Art. 553)
Grounding (earthing) and bonding (Art. 250)
Marinas and boatyards (Art. 555)
Radio and television equipment (Art. 810)
Services (Art. 230)
Solar photovoltaic systems (Art. 690)
Swimming pools, fountains, and similar installations (Art. 680)