Electrical Services — Part 1

Feb 1, 2009 12:00 PM, By Mike Holt, NEC Consultant

Understanding the requirements for the conductors supplying your service, including an in-depth look at Article 230

If you look at Fig. 230.1 in the NEC, you'll see that Art. 230 divides neatly into three general “blocks” of coverage. The first includes general requirements, overhead service drop conductors, and underground lateral conductors. These are covered by Art. 230 Parts I, II, and III, respectively.

Fig. 1. Per 230.7, mixing of service, feeder, and branch circuit conductors in the same service equipment enclosure is permitted.

The second and third blocks of Art. 230 provide requirements for service-entrance conductors and service equipment. We will address those in Part 2 of this article.

Number of services

Service drop conductors and underground lateral conductors are the conductors coming from the service point to the service entrance conductors or, sometimes, directly to the service equipment itself [see Art. 100 definitions starting with service and ending with service point].

Fig. 2. Overhead conductors must maintain a clearance of 3 ft from windows that open, doors, porches, balconies, ladders, stairs, fire escapes, or similar locations.

Utility-owned conductors before the service point are outside of the scope of the NEC [90.2(B)(5)]. Therefore, they have no definitions or requirements.

A building or structure can be served by only one service drop or service lateral [230.2]. The exceptions are:

Special conditions

Fire pumps
Emergency systems
Legally required standby systems
Optional standby systems
Parallel power production systems
Systems designed for connection to multiple sources of supply for the purpose of enhanced reliability
Keep them separate

For special occupancies, and with written consent from the Authority Having Jurisdiction (AHJ) [Art. 100 Special Permission]
Fig. 3. For 120/208V or 120/240V circuits, conductor clearance can be 18 in., if no more than 6 ft of conductors pass over no more than 4 ft of roof.

Multiple-occupancy buildings where there's no available space for supply equipment accessible to all occupants

Clearances

Capacity requirements

A building or other structure so large that two or more supplies are necessary
Where the capacity requirements exceed 2,000A, or where the load requirements of a single-phase installation exceed the utility's capacity
Service-drop conductor sizing

By written consent of the AHJ [Art. 100 Special Permission]

You can also have additional services for different voltages, frequencies, or phases — or for different uses, such as for different electricity rate schedules.

Fig. 4. The rules in 800.133(B) and 830.133(B) prohibit communications and broadband cables from being attached to raceways, including a service mast.

Where a structure is supplied by more than one service — or a combination of feeders and services — you must install a permanent plaque or directory at each service or building disconnect location to denote all other services and feeders supplying that structure (and the area served by each).

If you want a separate service for emergency or legally required systems [700.12(D) and 701.11(D)], you must get AHJ approval for it.

If you are using a separate service for a fire pump, emergency system, or standby power system, the disconnect must be located remotely away from the normal power disconnect [230.72(B)]. The reason for this requirement is to minimize the possibility of accidental interruption.

Service conductors must not pass through the interior of another structure [230.3]. Nor can you install them in the same raceway or cable with feeder or branch-circuit conductors [230.7].

This rule doesn't prohibit the mixing of service, feeder, and branch-circuit conductors in the same service equipment enclosure (Fig. 1 on page 24).

Overhead service conductors installed in a cable, or as individual open conductors, must be at least 3 ft from doors, porches, balconies, ladders, stairs, fire escapes, or similar locations [230.9(A)]. They must also be at least 3 ft from windows that open. If they run above a window, you don't have to maintain the 3 ft distance to that window (Fig. 2 on page 24).

Maintain a vertical clearance of at least 10 ft above platforms, projections, or surfaces from which people might reach an overhead conductor [230.9(B) and 230.24(B)]. This vertical clearance must be maintained for 3 ft, measured horizontally from the platform, projections, or surfaces from which people might reach them, except:

If the slope of the roof exceeds 4 in. of vertical rise for every 12 in. of horizontal run, 120/208V or 120/240V conductor clearances can be reduced to 3 ft over the roof [240.24(B) Ex 2].
If no more than 6 ft of conductors pass over no more than 4 ft of roof, 120/208V or 120/240V conductor clearances over the roof overhang can be reduced to 18 in. [240.24(B) Ex 3] (Fig. 3).

Don't install service conductors under an opening through which materials might pass, nor where they will obstruct entrance to building openings [230.9(C)]. Finally, don't use vegetation as support [230.10].

Service-drop conductors must have adequate mechanical strength, and they must have sufficient ampacity to carry the load as calculated in Art. 220 [230.23].

Ungrounded service-drop conductors can't be smaller than 8 AWG copper or 6 AWG aluminum, except in limited-load installations, where they can be as small as 12 AWG [230.23(B)].

Continue on Page 2

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Electrical Services — Part 2

Looking at Fig. 230.1 in the NEC, we can see that the second and third major areas of Art. 230 provide requirements for service entrance conductors (Part...

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