Outdoor Overhead Requirements

New Article 399 in the 2011 National Electrical Code (NEC) covers requirements for outdoor overhead conductors rated over 600 volts (V) that are used for the installation of feeders or branch circuits located on the load side of the service point. Articles 399 and 225 are worth a discussion of their permitted use.

The 2008 NEC does not provide requirements for installing outside overhead conductors rated over 600V. Article 399 was accepted in an effort to provide and improve the requirements where feeders and branch circuits over 600V are routed outside and overhead. The NEC has always had jurisdiction and regulation of the conductors and equipment installed on the load side of a service point. Such conductors may be:

1. Switched at the service point where power is derived without installing overcurrent protection and providing service equipment at that point of delivery
2. Feeders from substations or other service points that are used to distribute power to multibuildings or structures as permitted in 225.30 and 225.32
3. Outside overhead branch-circuits from service equipment that is designed and installed to supply power to industrial equipment that is too large to be supplied by systems of 600V or less

The 2008 NEC does not provide requirements for installing outside overhead conductors. Therefore, designers had to seek guidance from other standards and apply those requirements.

The National Electrical Safety Code (NESC) is most often referred to for the requirements pertaining to such systems. Of course, the NESC is used by utilities on the supply side of the service point and really should not be used on the load side of the service point. The NEC has always been used on the load side of the service point, and Article 399 is an effort to improve the requirements for feeders and branch circuits that are supplied by overhead conductors rated over 600V on the load side of the service point. Article 100 of the 2011 NEC defines service point.

The new Section 399.30 contains performance--based requirements for supporting, spacing and installation of overhead conductors; their support structures; and insulators on cross arms used for installation of such systems.

Since the requirements in Section 399.30 are performance--based, the informational note for 399.10 refers users to the NESC to obtain design and installation requirements. However, designing engineers may use their own requirements if they do not conflict with another standard. Note that 399.30 requires that only a licensed professional engineer can design these systems, and they must provide appropriate documentation.

Disconnecting means—225.52(C) and (D)
Two new subdivisions have been accepted to 225.52 that govern the disconnecting means for systems over 600V. Subdivision (C) covers the means of locking out a disconnecting means. Basically, it must be provided with a means to lock it out in the open position without the use of a special locking device. The locking means must remain when the lock has been removed. See the exception for disconnects with or enclosing fused cutouts. Subdivision D states that all disconnects must be clearly marked to indicate whether they are in the open or closed position. The up position of the disconnect handle must indicate “on.” Down must indicate “off.”

Disconnecting means—225.52(E) and (F)
New subdivision E requires a uniform position for these disconnects. Disconnect handles that are operated in the up position (vertically) must indicate “on,” and when in the down position, they must indicate “off.” Subdivision F requires feeders or branch circuits supplying or passing through a building or structure to be identified with a permanent plaque or directory denoting all other sources of power.

Inspection and tests—225.56
Subdivision E requires pre-energization and operating tests for systems over 600V when these systems are first installed. Every component, such as protective, switching and control circuitry, must be adjusted by the provisions that are recommended by the manufacturer of the protective device study and properly tested by an appropriate operational test. The results of the test report must be available to the authority having jurisdiction.

For the first time, new section 225.70 contains requirements covering the installation of substations located on the load side of the service point. Requirements for the installation of feeders and branch circuits also are covered.For example, feeders can be routed per Article 399 from substations and supply power to buildings or structures.
In conclusion, engineers and contractors must review this new article as well as the other sections outlined to ensure that these systems over 600V are installed properly.


STALLCUP is the CEO of Grayboy Inc., which develops and authors publications for the electrical industry and specializes in classroom training on the National Electrical Code and other standards, including those from OSHA. Contact him at 817.581.2206.

About the Author

James G. Stallcup

Code Contributor
James G. Stallcup is the CEO of Grayboy Inc., which develops and authors publications for the electrical industry and specializes in classroom training on the NEC and OSHA, as well as other standards. Contact him at 817.581.2206.

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