Article 230 - Services

By Mike Holt for EC&M Magazine

Part I. General

Author’s Comment: Understanding where the service begins and where it ends is critical in the proper application of many Code rules. To understand how to apply these rules, we need to review the following definitions from Article 100.

Service point - The point of connection between the facilities of the serving utility and the premises wiring.

Service conductors - The conductors from the service point to the service disconnecting means (service equipment, not meter). Service conductors would include service-entrance conductors for both overhead (service drop) and underground (service lateral).

Service equipment - The necessary equipment, usually consisting of circuit breakers or switches and fuses and their accessories, connected to the load end of service conductors to a building or other structure, or an otherwise designated area, and intended to constitute the main control and cutoff of the supply. Service equipment does not include the metering equipment, such as the meter and/or meter enclosures [230.66].

After reviewing these three definitions, you should understand that service conductors originate at the serving utility (service point) and terminate on the line side of the service disconnecting means (service equipment). Conductors and equipment on the load side of service equipment are considered feeder conductors

End of author’s comment

230.1 Scope

Article 230 covers the installation requirements for service conductors and equipment.

230.2 Number of Services. A building or structure can be served by only one service (service drop or service-lateral), except as permitted by (A) through (D). Figure 230-2 230-02 01.cdr
(A) Special Conditions.
(1) Fire pumps
(2) Emergency power
(3) Legally required standby power
(4) Optional standby power
(5) Parallel power production systems.

(B) Special Occupancies. By special permission, additional services are permitted for:
(1) Multiple-occupancy buildings where there is no available space for supply equipment accessible to all occupants, or
(2) A building or other structure so large that two or more supplies are necessary.

(C) Capacity Requirements. Additional services are permitted:
(1) Where the capacity requirements are in excess of 2,000A at a supply voltage of 600V or less.
(2) Where the load requirements of a single-phase installation exceed the utility’s normal capacity.
(3) By special permission.

(D) Different Characteristics. An additional service is permitted for different voltages, frequencies, or phases, or for different uses, such as for different electricity rate schedules.

(E) Identification of Multiple Services. Where a building or structure is supplied by more than one service, or a combination of branch circuits, feeders, and services, a permanent plaque or directory must be installed at each service, feeder, or branch circuit disconnect location denoting all other services, feeders, and branch circuits supplying that building or structure and the area served by each. Figure 230-3 230-02E.cdr

230.3 Pass Through a Building or Structure

Service conductors cannot pass through the interior of another building or other structure.

230.6 Conductors Considered Outside a Building. Conductors are considered outside a building when they are installed:
(1) Under not less than 2 in. of concrete beneath a building or structure.
(2) Within a building or structure in a raceway that is encased in no less than 2 in. thick of concrete or brick.
(3) Installed in a vault that meets the construction requirements of Article 450, Part III.
(4) In conduit under not less than 18 in. of earth beneath a building or structure.

Author’s Comment: Service conductors must not be installed inside a building [230-70(A)(1)], but if the raceway is below a building, the service conductors are considered outside the building. Figure 230-4 230-06(1).cdr

230.7 Service Conductors Separate From Other Conductors

Service conductors must not be installed in the same raceway or cable with feeder or branch circuit conductors.

Author’s Comment: This rule does not prohibit the mixing of service, feeder, and branch-circuit conductors in the same “service equipment enclosure”. Figure 230-5 230-07 01.cdr

WARNING: Overcurrent protection for the feeder conductors could be bypassed if we mixed service conductors with other conductors in the same raceway and a fault occurred between the service and feeder conductors.

Author’s Comment: This requirement may be the root of the misconception that “line” and “load” conductors are not permitted in the same raceway. It is true that service conductors are not permitted in the same raceway with feeder or branch-circuit conductors, but line and load conductors of feeders and branch circuits can be in the same raceway, cable, or enclosure. Figure 230-6 230-07 02.cdr

230.9 Clearance From Building Openings

(A) Clearance From Windows. Overhead service conductors must maintain a clearance of 3 ft from windows that are designed to be opened, doors, porches, balconies, ladders, stairs, fire escapes, or similar locations. Figure 230-7 230-09A.cdr

Exception: Overhead conductors run above a window are not required to maintain the 3 ft distance.

(B) Vertical Clearance. Overhead service conductors must maintain a vertical clearance of not less than 10 ft above platforms, projections or surfaces from which they might be reached [230.24(B)]. This vertical clearance must be maintained for 3 ft measured horizontally from the platform, projections or surfaces from which they might be reached.

(C) Below Opening. Service conductors cannot be installed under an opening through which materials might pass, and they must not be installed where they will obstruct entrance to building openings. For example, the upper opening in a barn loft is often used to move hay in or out of the loft storage area. Figure 230-8 230-09C.cdr

230.10 Vegetation as Support

Vegetation such as trees cannot be used for the support of overhead service conductors. Figure 230-9 230-10 cc230-01.cdr

Part II. Overhead Service-Drop Conductors

Author’s Comment: Overhead service-drop conductors installed by the electric utility must be in accordance with the National Electric Safety Code (NESC), not the NEC [90.2(B)(5)], but overhead service conductors not under the exclusive control of the electric utility must be installed in accordance with the NEC.

230.24 Clearances

Service-drop conductors must be located so that they are not readily accessible, and they must comply with the following clearance requirements:
(A) Above Roofs. Overhead service conductors must maintain a minimum clearance of 8 ft above the surface of a roof for a minimum distance of 3 ft in all directions from the edge of the roof.

Exception No. 2: Where the voltage does not exceed 300V between conductors, overhead conductor clearances from the roof can be reduced from 8 ft to 3 ft, if the slope of the roof exceeds 4 in. in 12 in.

Exception No. 3: If the voltage between conductors does not exceed 300V, the conductor clearance over the roof overhang can be reduced from 8 ft to 1.5 ft, if no more than 6 ft of overhead conductors pass over no more than 4 ft of roof overhang, and the conductors terminate at a through-the-roof raceway or approved support. Figure 230-10 230-24Ax3.cdr

Exception No. 4: The 3 ft vertical clearance that extends from the roof does not apply when the point of attachment is on the side of the building below the roof.

(B) Clearances. Overhead conductor spans for system not over 600V must maintain the following clearances: Figure 230-11 230-24B.cdr

(1) 10 ft at the electric service entrance to buildings, at the lowest point of the drip loop of the building electric entrance, above finished grade, sidewalks, or platform or projection from which they might be accessible to pedestrians, where the voltage is not in excess of 150V to ground.
(2) 12 ft above residential property and driveways, and those commercial areas not subject to truck traffic, where the voltage does not exceed 300V to ground.
(3) 15 ft above those areas listed in the 12 ft classification, where the voltage exceeds 300V to ground.
(4) 18 ft over public streets, alleys, roads, parking areas subject to truck traffic, driveways on other than residential property, and other areas traversed by vehicles such as cultivated, grazing, forest, and orchard. Department of Transportation (DOT) type right of ways in rural areas are many times used by slow-moving and tall farming machinery to avoid impeding traffic flow.

(D) Swimming Pools. Service conductors above pools, diving structures, observation stands, towers, or platforms must comply with 680.8.

230.26 Point of Attachment

The point of attachment for service-drop conductors must not be less than 10 ft above the finish grade and must be located so that the minimum service conductor clearance required by 230.24(B) can be maintained.

CAUTION: Conductors might need to have the point of attachment raised higher so that the overhead conductor will comply with the clearances required by 230.24. Figure 230-12 230-26.cdr

230.28 Service Masts Used as Supports

The service mast must have adequate mechanical strength, or braces or guy wires must support it, to withstand the strain caused by the service-drop conductors as determined by the AHJ.

Author’s Comment: Some local building codes require a minimum 2 in. rigid metal conduit to be used for the service mast. In addition, many electric utilities contain specific requirements for the service mast.

Only electric utility service-drop conductors can be attached to a service mast, and then only with listed devices.

Author’s Comment: Sections 810.12 and 820.10(C) specify that aerial cables for radio, TV, or CATV cannot be attached to the electric service mast, and 810.12 prohibits antennas from being attached to the service mast. In addition 800.52(E) and 830.58(D) prohibits communications cables from being attached to raceways, including a service mast for power conductors. Figure 230-13 230-28.cdr

Part III. Underground Service Lateral Conductors

Author’s Comment: Underground service-lateral conductors installed by the electric utility must be in accordance with the National Electric Safety Code (NESC), not the NEC [90.2(B)(5)], but underground conductors not under the exclusive control of the electric utility must be installed in accordance with the NEC.

Part IV. Service-Entrance Conductors

230.40 Number of Service-Entrance Conductor Sets. Each service drop or lateral must supply only one set of service-entrance conductors.

Exception No. 1: Buildings with more than one occupancy can have one set of service-entrance conductors for each service of different characteristics [230.2(D)] run to each occupancy.

Exception No. 2: One set of service-entrance conductors can supply two to six service disconnecting means as permitted in 230.71(A).

Exception No. 3: A single-family dwelling unit with a separate structure can have one set of service- entrance conductors run to each structure from a single service drop or lateral.

230.42 Size and Rating
(A) Load Calculations. Service-entrance conductors must have sufficient ampacity for the loads to be served in accordance with Article 220.
(1) Continuous Loads. Service conductors that supply continuous loads must be sized no less than 125 percent of the continuous loads, plus 100 percent of the noncontinuous loads. The conductor is selected based on the conductor ampacities as listed in Table 310.16, before any ampacity adjustment in accordance with the terminal rating [110.14(C)].

Question. What size service conductor is required for 184A continuous load if the terminals are rated for 75C? Figure 230-14 230-42A1.cdr

Answer: 4/0 AWG
Step 1. Size the conductors at 125 percent of the load [215.2(A)(1)].
184A load x 1.25 = 230A, 4/0 AWG THHN is rated 230A at 75C, Table 310.16

Author’s Comment: Feeder protection devices must be sized no smaller than 125 percent of the continuous load 184A load x 1.25 = 230A, next size up 250A [230.42(A)(1) and 240.6(A)].

(C) Grounded (neutral) Conductor Size. The grounded (neutral) service conductor must be sized to carry the maximum unbalanced load in accordance with 220.22 and must not be sized smaller than required by 250.24(B).

230.43 Wiring Methods.

Service conductors must be installed in one of the following wiring methods:
(1) Open wiring on insulators
(3) Rigid metal conduit, RMC
(4) Intermediate metal conduit, IMC
(5) Electrical metallic tubing, EMT
(6) Electrical nonmetallic tubing, ENT
(7) Service-entrance cables, SE or USE
(8) Wireway
(9) Busway
(11) Rigid nonmetallic conduit, RNC
(13) Type MC cable
(15) Flexible metal conduit or liquidtight flexible metal conduit not over 6 ft long
(16) Liquidtight flexible nonmetallic conduit

Part V. Service Equipment - General

230.66 Identified as Suitable for Service Equipment

The service disconnecting means must be identified as suitable for use as service equipment. This means that the disconnect must be supplied with a main bonding jumper [250.28] so that a neutral-to-case connection can be made as required in 250.24(B). Figure 230-17 230-66.cdr.

Individual meter cans are not considered service equipment.

Part VI. Service Equipment - Disconnecting Means

230.70 General

The service disconnect must disconnect all service-entrance conductors from the building or structure premises wiring.

(A) Location.
(1) Readily Accessible. The service disconnect must be at a readily accessible location either outside the building or structure, or inside nearest the point of entry of the service conductors.

WARNING: Service conductors do not have short circuit or ground fault protection, so they must be limited in length when installed inside a building. Some local jurisdictions have a specific requirement as to the maximum length permitted within a building. Figure 230-18 230-70A.cdr.

Author’s Comment: If the service disconnect is outdoors, the NEC does not require it to be located on the building or structure. Check with the AHJ on how far the disconnecting means can be from the building.

(2) Bathrooms. The service disconnecting means cannot be installed in a bathroom. Figure 230-19 230-70A2.cdr

(3) Remote Control of Service Disconnect. Where a remote-control device is used to actuate the service disconnecting means, the service disconnecting means must be at a readily accessible location either outside the building or structure, or nearest the point of entry of the service conductors as required by 230.70(A)(1). Figure 230-20 230-70A3 cc230-03.cdr

Author’s Comment: The construction of the disconnecting means must be in accordance with 230.76, and a pushbutton that activates the electromagnetic coil of a shunt-trip circuit breaker will not meet this requirement. See 230.71(A) and 230.76.

(B) Disconnect Identification. Each service disconnect must be permanently marked to identify it as part of the service disconnecting means. See 110.22, which requires all disconnecting means to be legibly marked to indicate their purpose. In addition, the marking must be of sufficient durability to withstand the environment involved. Figure 230-21 230-70B.cdr

Author’s Comment: When a building or structure has two or more services, a plaque is required at each service location to show the location of the other service. See 230.2(E).

(C) Suitable for the Conditions. Service disconnecting means must be suitable for the prevailing conditions.

230.71 Number of Disconnects

(A) Maximum. There must be no more than six disconnects for each service permitted by 230.2, or each set of service-entrance conductors permitted by 230.40, Ex. 1, 3, 4 or 5.

CAUTION: The rule is six disconnects for each service, not each building. If the building can have two services, then there can be a total of twelve disconnects: two groups of six. Figure 230-22 230-71A 01.cdr.

The service disconnecting means can consist of up to six switches or six circuit breakers mounted in a single enclosure, in a group of separate enclosures, or in or on a switchboard. Figure 230-23 230-71A 02.cdr.

A remote-control device with a shunt-trip push button used to open the service disconnecting means is not considered a service disconnecting means. See 230.70(A)(3) and 230.76.

230.72 Grouping of Disconnects

(A) Two to Six Disconnects. The disconnecting means for each service must be grouped.

(B) Fire Pump and Stand-by Power Service. To minimize the possibility of accidental interruption of power, the disconnecting means for fire pumps or standby power services, as permitted in 230.2(A)(1), must be located remotely away from the two to six disconnects for normal service.

(C) Access to Occupants. In a multiple-occupancy building, each occupant must have access to his or her disconnecting means.

Exception: In multiple-occupancy buildings where electrical maintenance is provided by continuous building management, the service disconnecting means can be accessible only to building management personnel.

230.82 Equipment on the Supply Side.

Electrical equipment must not be connected to the supply side of the service disconnect enclosure, except:
(2) Meters rated not in excess of 600V.
(4) Tap conductors for legal and optional standby power systems, fire pump equipment, fire and sprinkler alarms, and load (energy) management devices

Author’s Comment: Where acceptable to the AHJ, connections ahead of and not within the same cabinet, enclosure, or vertical switchboard section of the service disconnecting means can supply legally required standby power [701.11(E)], but emergency standby power cannot be connected ahead of service equipment. Figure 230-25 230-82(4).cdr

(5) Solar photovoltaic systems, fuel-cell systems, or interconnected electric power production sources.

Part VII. Service Equipment Overcurrent Protection

Author’s Comment: The NEC does not require that service conductors be provided with short-circuit or ground-fault protective equipment.

230.90 Overload Protection Required. Each ungrounded service conductor must have overload protection at the point where the service conductors terminate. See 240.21(D).

(A) Overcurrent Protection Size. The rating of the protection device must not be greater than the ampacity of the conductors.

Exception No. 2: Where the ampacity of the conductors does not correspond with the standard rating of overcurrent protection devices as listed in 240.6(A), the next higher protection device can be used, if it does not exceed 800A in accordance with 240.4(B).

For example, two sets of 500 kcmil THHN conductors (each rated 380A at 75C) can be protected by an 800A overcurrent protection device. Figure 230-26 230-90Ax2.cdr

Author’s Comment: Typically conductors are sized to the 75C ampacity listed in Table 310.16. See 110.14(C) for more information.

Exception No. 3: The sum of the ratings of two to six circuit service disconnecting means can exceed the ampacity of the service conductors, provided the calculated load in accordance with Article 220 does not exceed the ampacity of the service conductors. Figure 230-27 230-90Ax3.cdr

Exception No. 5: Overload protection for single-phase, 3-wire, 120/240V dwelling service conductors can be in accordance with the requirements of 310.15(B)(6). Figure 230-28 230-90Ax5.cdr

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