By Mike Holt for EC&M Magazine
Part I. General
Authors 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 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 authors comment
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
(B) Special Occupancies. By special permission, additional
services are permitted for:
(C) Capacity Requirements. Additional services are permitted:
(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
230.3 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:
Authors 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.
Authors 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.
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
Authors 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.
Service-drop conductors must be located so that they are not
readily accessible, and they must comply with the following clearance requirements:
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.
(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.
Authors 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.
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
Part III. Underground Service Lateral Conductors
Authors 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
Question. What size service conductor is required for 184A continuous load if the terminals are rated for 75ºC? Figure 230-14 230-42A1.cdr
Answer: 4/0 AWG
Authors 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
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
The service disconnect must disconnect all service-entrance conductors from the building or structure premises wiring.
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.
Authors 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
Authors 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
Authors 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:
Authors 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
Authors 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 75°C) can be protected by an 800A overcurrent protection device. Figure 230-26 230-90Ax2.cdr
Authors Comment: Typically conductors are sized to the 75°C 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
Copyright © 2002 Mike Holt Enterprises,Inc.