NEC 230 — Services (Washington)

NEC 230 — Services (Washington Journeyman)

Learning Objectives

1.1 Number of Services, Routing, and Outside the Building

Article 230 covers service conductors and the equipment controlling services not over 1000 volts ac or 1500 volts dc, nominal (230.1). A building shall be supplied by only one service unless an additional service is permitted by 230.4(A) through 230.4(D), which cover special occupancies, capacity above 2000 amperes at 1000 volts or less, and different characteristics such as voltage, frequency, phase, or rate schedule. A permanent plaque or directory shall be installed at each service disconnect location denoting the loads and area served (230.4(E)), and service conductors supplying a building shall not pass through the interior of another building or other structure (230.5).

230.6 nevertheless treats conductors as outside a building when they are:

Wood encasement never satisfies 230.6(2), and a run that pierces a wall does not satisfy 230.6(5). Circuit conductors other than service conductors shall not share raceways, cables, handhole enclosures, or underground boxes with service conductors (230.7), except grounding electrode conductors or supply side bonding jumpers (Exception No. 1) and overcurrent-protected load management control conductors (Exception No. 2). A service raceway entering a building shall be sealed in accordance with 300.7(G) and 300.9(A), and spare or unused raceways shall also be sealed (230.8).

1.2 Service-Entrance Conductors: Insulation, Size, Ampacity, Supports

Individual conductors shall be insulated or covered, except that the grounded conductor of a multiconductor cable may be bare (230.22), and service-entrance conductors entering or on the exterior of a building shall be insulated (230.41). The exception to 230.41 permits an uninsulated grounded conductor only as bare copper in a raceway or service cable assembly, as bare copper for direct burial where approved for the soil conditions or where part of a cable assembly identified for underground use, or as aluminum or copper-clad aluminum forming part of a cable assembly identified for underground use. Minimum size is 8 AWG copper or 6 AWG aluminum or copper-clad aluminum under 230.23(B) and 230.31(B), except that conductors supplying only limited loads of a single branch circuit shall not be smaller than 12 AWG copper or 10 AWG aluminum or copper-clad aluminum.

Ampacity begins at 310.16 after the adjustment and correction factors of 310.14: underground service conductors shall have an ampacity not less than the calculated load (230.31(A)), and service-entrance conductors at least the maximum calculated load, and not less than the sum of the noncontinuous loads plus 125 percent of the continuous loads where continuous loads are supplied (230.42(A)(1)). 230.42(B) requires the minimum ampacity of ungrounded conductors to be not less than the rating of the service disconnecting means specified in 230.79(A) through 230.79(D). Article 230 never sizes the grounded conductor itself: 230.31(C) and 230.42(C) require it to be not smaller than the minimum size required by 250.24(D), while Table 250.66 sizes the grounding electrode conductor and Table 250.122 the equipment grounding conductors.

Supports come from 230.51: service-entrance cables need support within 300 mm (12 in.) of every service head, gooseneck, or connection and at intervals not exceeding 750 mm (30 in.) (230.51(A)); cables not approved for contact mounting use insulating supports at intervals not exceeding 4.5 m (15 ft) with a clearance of not less than 50 mm (2 in.) from the surface over which they pass (230.51(B)); and individual open conductors follow Table 230.51(C), on insulators or insulating supports where exposed to the weather and on glass or porcelain knobs where not (230.51(C)).

1.3 Overhead Clearances, Point of Attachment, Masts, and Protection

Overhead service conductors shall not be readily accessible and shall comply with 230.24(A) through 230.24(E). Under 230.24(A) the clearance above a roof surface is not less than 2.6 m (8 ft 6 in.), maintained for not less than 900 mm (3 ft) in all directions from the edge of the roof; Exception No. 2 reduces that to 900 mm (3 ft) where the voltage between conductors does not exceed 300 and the roof slope is 100 mm in 300 mm (4 in. in 12 in.) or greater; and Exception No. 3 permits 450 mm (18 in.) above only the overhanging portion of the roof where not more than 1.8 m (6 ft) of overhead conductors and 1.2 m (4 ft) horizontally pass above the overhang and terminate at a through-the-roof raceway or approved support.

Clearance from final grade is the separate list of 230.24(B): 3.0 m (10 ft) at the service entrance, at the lowest point of the drip loop, and over areas or sidewalks accessible only to pedestrians; 3.7 m (12 ft) over residential property and driveways and commercial areas not subject to truck traffic where the voltage does not exceed 300 volts to ground; 4.5 m (15 ft) over those areas where the voltage exceeds 300 volts to ground; 5.5 m (18 ft) over public streets, alleys, roads, parking areas subject to truck traffic, driveways on other than residential property, and land such as cultivated, grazing, forest, and orchard; and 7.5 m (24 1/2 ft) over tracks of railroads.

On the building, 230.9(A) requires open conductors or multiconductor cable without an overall outer jacket to clear windows designed to be opened, doors, porches, balconies, ladders, stairs, fire escapes, and similar locations by not less than 900 mm (3 ft). The point of attachment shall provide those clearances and shall never be less than 3.0 m (10 ft) above finished grade (230.26). Service masts shall be of adequate strength, or supported by braces or guy wires, to withstand safely the strain imposed by the service-drop or overhead service conductors (230.28(A)).

For physical protection, service-entrance cables subject to damage shall be protected by RMC, IMC, Schedule 80 PVC conduit, EMT, RTRC, or other approved means (230.50(B)(1)), and individual open conductors and other cables shall not be installed within 3.0 m (10 ft) of grade level (230.50(B)(2)).

1.4 Service Heads, Goosenecks, Raceway Seals, and Service Equipment

Each service drop, set of overhead service conductors, set of underground service conductors, or service lateral shall supply only one set of service-entrance conductors (230.40), with the exceptions stated there.

A service head shall be installed where a service raceway connects to service-drop or overhead service conductors and shall be listed for use in wet locations (230.54(A)). Service-entrance cables shall be equipped with a service head or gooseneck, and Type SE cable may be formed in a gooseneck and taped with a self-sealing weather-resistant thermoplastic (230.54(B)). Service heads and goosenecks shall be located above the point of attachment of the service-drop or overhead service conductors, or, where impracticable, not farther than 600 mm (24 in.) from that point (230.54(C)), and service heads shall have conductors of different potential brought out through separately bushed openings, except for jacketed multiconductor service-entrance cable without splice (230.54(E)).

Raceways enclosing service-entrance conductors exposed to the weather shall be listed or approved for use in wet locations and arranged to drain, and where embedded in masonry they shall be arranged to drain (230.53). Where individual open conductors enter a building they shall enter through roof bushings or through the wall in an upward slant through individual, noncombustible, nonabsorbent insulating tubes, with drip loops formed before they enter the tubes (230.52). A raceway or sleeve passing from the interior to the exterior is subject to 300.9(A), which requires sealing against circulation of warm air into a colder section.

Service-entrance conductors are limited to the wiring methods of 230.43, including RMC, IMC, EMT, service-entrance cables, wireways, busways, and Type MC and Type MI cable, and spliced or tapped conductors must be marked or identified as suitable for use on the line side of the service equipment (230.46).

1.5 Service Disconnecting Means: Location, Number, Grouping, Rating

230.70 requires means to disconnect all ungrounded conductors in a building from the service conductors, then fixes where they may be. For one- and two-family dwellings, 230.70(A)(1) requires a readily accessible outdoor location, on the dwelling unit or within sight of it in accordance with 110.29, unless an emergency disconnect is installed per 225.41. For other occupancies, 230.70(A)(2) requires a readily accessible location either outside the building or inside nearest the point of entrance of the service conductors, and 230.70(A)(3) prohibits installation in bathrooms. Service disconnects shall be marked “SERVICE DISCONNECT” and, for one- and two-family dwellings, “EMERGENCY DISCONNECT” on the outside front with letters at least 13 mm (1/2 in.) high (230.70(B)).

Each service shall have only one service disconnect unless 230.71(B) is met, which permits two to six service disconnects for each service permitted by 230.4 or for each set of service-entrance conductors permitted by 230.40 Exception No. 1, No. 3, No. 4, or No. 5, in separate enclosures with a single disconnect in each or in the assemblies listed in the section. Disconnects used solely for power monitoring equipment, surge-protective devices, ground-fault protection control circuits, or the control circuit of a power-operable service disconnect are not counted (230.71(A)). The two to six disconnects shall be grouped, and each shall be marked to indicate the load served (230.72(A)); disconnecting means for fire pumps, emergency systems, and standby services permitted by 230.4 shall be installed remote from the normal-service disconnects (230.72(B)); and in a multiple-occupancy building each occupant shall have access to the occupant’s service disconnecting means (230.72(C)).

Each service disconnect shall simultaneously disconnect all ungrounded service conductors it controls from the premises wiring system (230.74), and where it does not disconnect the grounded conductor other means shall be provided in the service equipment (230.75). The disconnect shall be a manually operable switch or circuit breaker with a handle or other suitable operating means, or a power-operated switch or circuit breaker that can be opened by hand in the event of a power supply failure (230.76), and it shall plainly indicate whether it is in the open (off) or closed (on) position (230.77).

Rating is the highest-yield topic here. The service disconnecting means shall have a rating not less than the calculated load and not less than 230.79(A) through 230.79(D):

Take the larger of the load and the floor, then round up to the next standard rating in 240.6(A) — 15, 20, 25, 30, 60, 70, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, or 400 amperes. A calculated load of 185 amperes requires 200 amperes; 340 amperes requires 350 amperes; a dwelling load of 95 amperes requires 100 amperes; and a dwelling load of 105 amperes requires 110 amperes, because the dwelling floor is a minimum and not a waiver of the load rule. Where the disconnecting means consists of more than one switch or circuit breaker permitted by 230.71, the combined ratings shall not be less than the rating required by 230.79 (230.80), and only the equipment listed in 230.82 may be connected on the supply side of the service disconnect. Each ungrounded service conductor shall have overload protection by an overcurrent protective device having a rating or setting not higher than the ampacity of the conductor (230.90).

1.6 Grounding and Bonding at the Service

Article 230 repeatedly hands off to Article 250: 230.23(C), 230.31(C), and 230.42(C) each require the grounded conductor to be not smaller than the minimum size required by 250.24(D). 250.24(A) requires a premises wiring system supplied by a grounded ac service to have a grounding electrode conductor connected to the grounded service conductor at each service. 250.24(B) states the load-side rule: a grounded conductor shall not be connected to normally non-current-carrying metal parts of equipment, to equipment grounding conductor(s), or be reconnected to ground on the load side of the service disconnecting means except as otherwise permitted in Article 250. 250.24(C) requires an unspliced main bonding jumper to connect the equipment grounding conductor(s) and the service-disconnect enclosure to the grounded conductor within the enclosure, in accordance with 250.28.

250.24(D) controls the grounded conductor: if an ac system of 1000 volts or less is grounded at any point, the grounded conductor(s) shall be routed with the ungrounded conductors to each service disconnecting means and connected to each disconnecting means grounded conductor terminal or bus, with a main bonding jumper connecting it to each enclosure. Under 250.24(D)(1) it shall not be smaller than Table 250.102(C)(1) in a single raceway or cable, and under 250.24(D)(2) where ungrounded service-entrance conductors are paralleled in two or more raceways or cables the grounded conductors shall be installed in each raceway or cable and connected in parallel, sized from that table but never smaller than 1/0 AWG. 250.24(E) requires the grounding electrode conductor to be sized in accordance with 250.66.

250.28 governs the main bonding jumper: it may be a wire, bus, screw, or similar suitable conductor of copper, aluminum, copper-clad aluminum, or another corrosion-resistant material (250.28(A)), and it shall be sized per 250.28(D)(1) through 250.28(D)(3). Under 250.28(D)(1) it shall not be smaller than Table 250.102(C)(1), and under 250.28(D)(2), where a service consists of more than a single enclosure as permitted in 230.71(B), the main bonding jumper for each enclosure is sized on the largest ungrounded service conductor serving that enclosure. The copper rows of Table 250.102(C)(1) are:

Note 1: if the circular mil area of ungrounded supply conductors connected in parallel exceeds 1100 kcmil copper or 1750 kcmil aluminum, the grounded conductor or bonding jumper shall have an area not less than 12 1/2 percent of the area of the largest ungrounded supply conductor or equivalent area for parallel supply conductors; Note 2: it need not be larger than the largest ungrounded conductor. A 1200-kcmil copper ungrounded service conductor falls in the over 1100 row, so Note 1 governs and 3/0 AWG copper satisfies it, while a 600-kcmil copper conductor is in the over 350 through 600 row and takes 1/0 copper.

Table 250.66 sizes the grounding electrode conductor on the largest ungrounded service conductor, using the largest sum of the areas of the corresponding conductors of each set where multiple sets connect directly to the supply. Equipment grounding conductors follow a third table and rule: Table 250.122 sizes them by the rating or setting of the overcurrent protective device ahead of the equipment — 6 AWG copper at 200 amperes, 8 AWG at 100 amperes, 4 AWG at 300 amperes, and 3/0 AWG at 1200 amperes.

1.7 Worked Method: Rating, Main Bonding Jumper, Grounding Electrode Conductor

Work in code order, because the code order fixes the arithmetic order. First classify the occupancy and find the floor in 230.79(A) through 230.79(D): 15 amperes, 30 amperes, 100 amperes for a one-family dwelling, 60 amperes for all other installations. Second, take the larger of the calculated load and the floor and round up to the next standard rating in 240.6(A): loads of 185 and 340 amperes give 200 and 350 amperes, and a dwelling load of 95 amperes gives 100 amperes. Third, carry that rating into 230.42(B), where the ungrounded service-entrance conductors may not have an ampacity below the rating selected from 230.79(A) through 230.79(D).

Then size the conductors and jumpers. The grounding electrode conductor comes from Table 250.66 on the largest ungrounded service conductor, using the largest sum of areas of corresponding conductors when multiple sets connect to the supply. The grounded conductor and main bonding jumper come from Table 250.102(C)(1) under 250.28(D)(1) and 250.24(D)(1): a single 1200-kcmil copper conductor takes 3/0 AWG copper under Note 1, while a 600-kcmil copper conductor takes 1/0 copper. For a parallel set such as two 350-kcmil copper conductors per phase, the table is applied to the equivalent area rather than to one conductor, and the grounded conductors go in each raceway or cable and are never smaller than 1/0 AWG under 250.24(D)(2).

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Summary

Article 230 is a chain of decisions. The service is singular — one service per building unless 230.4(A) through 230.4(D) applies, with identification under 230.4(E) — and service conductors stay out of building interiors under 230.5 except where 230.6 considers them outside: concrete or brick of 50 mm (2 in.), the Article 450 Part III vault, 450 mm (18 in.) of earth, or RMC or IMC through an eave but not a wall to meet 230.24. Raceways entering a building are sealed per 300.7(G) and 300.9(A) under 230.8, and only the conductors allowed by 230.7 may share the service raceway. Overhead clearances come from 230.9 and 230.24 — the 2.6 m (8 ft 6 in.) roof clearance with its 900 mm (3 ft) and 450 mm (18 in.) exceptions, and grade clearances from 3.0 m (10 ft) to 7.5 m (24 1/2 ft) — with the point of attachment never below 3.0 m (10 ft) above finished ground under 230.26 and mast strength and attachment under 230.28. Grounding and bonding close the chain: an unspliced main bonding jumper sized from Table 250.102(C)(1) under 250.28, the grounded conductor brought to the service equipment under 250.24(D), the grounding electrode conductor from Table 250.66, and equipment grounding conductors from Table 250.122.