2, Exception No. 3.

Grounding conductors not an integral part of a cable assembly shall not be smaller than No. 6 copper or No. 4 aluminum. ARTICLE 280 - SURGE ARRESTERS A. General 280-1. Scope. This article covers general requirements, installation requirements, and connection requirements for surge arresters installed on premises wiring systems. 280-2. Definition. A surge arrester is a protective device for limiting surge voltages by discharging or bypassing surge current, and it also prevents continued flow of follow current while remaining capable of repeating these functions. 280-3. Number Required. Where used at a point on a circuit, a surge arrester shall be connected to each ungrounded conductor. A single installation of such surge arresters shall be permitted to protect a number of 70-140 NATIONAL ELECTRICAL CODE interconnected circuits provided that no circuit is exposed to surges while disconnected from the surge arresters. 280-4. Surge Arrester Selection. (a) On Circuits of Less than 1000 Volts. The rating of the surge arrester shall be equal to or greater than the maximum continuous phase-to-ground power frequency voltage available at the point of application. (b) On Circuits of 1 kV and Over-Silicon Carbide Types. The rating of a silicon carbide-type surge arrester shall be not less than 125 percent of the maximum continuous phase-to-ground voltage available at the point of application. (FPN No. 1): For further information on surge arresters, see Guide for the Application of Gapped Silicon-Carbide Surge Arresters for Alternating-Current Systems, C62.2-1988, and Standard for Metal Oxide Surge Arresters for Alternating- Current Power Circuits, ANSI/IEEE C62.11-1986. (FPN No. 2): The selection of a properly rated metal oxide arrester is based on considerations of maximum continuous operating voltage and the magnitude and duration of overvoltages at the arrester location as affected by phase-to-ground faults, system grounding techniques, switching surges, and other causes. See manufacturer's application rules for selection of the specific arrester to be used at a particular location. B. Installation 280-11. Location. Surge arresters shall be permitted to be located indoors or outdoors and shall be made inaccessible to unqualified persons. Exception: Surge arresters listed for installation in accessible locations. 280-12. Routing of Surge Arrester Connections. The conductor used to connect the surge arrester to line or bus and to ground shall not be any longer than necessary and shall avoid unnecessary bends. C. Connecting Surge Arresters 280-21. Installed at Services of Less than 1000 Volts. Line and ground connecting conductors shall not be smaller than No. 14 copper or No. 12 aluminum. The arrester grounding conductor shall be connected to one of the following: (1) the grounded service conductor; (2) the grounding electrode conductor; (3) the grounding electrode for the service; or (4) the equipment grounding terminal in the service equipment. 280-22. Installed on the Load Side Services of Less than 1000 Volts. Line and ground connecting conductors shall not be smaller than No. 14 copper or No. 12 aluminum. A surge arrester shall be permitted to be connected between any two conductors (ungrounded conductor(s), grounded conductor, grounding conductor). The grounded conductor and the grounding conductor shall be interconnected only by the normal operation of the surge arrester during a surge. ARTICLE 280 - SURGE ARRESTERS 70-141 280-23. Circuits of 1 kV and Over-Surge-Arrester Conductors. The conductor between the surge arrester and the line and surge arrester and the grounding connection shall not be smaller than No. 6 copper or aluminum. 280-24. Circuits of 1 kV and Over-Interconnections. The grounding conductor of a surge arrester protecting a transformer that supplies a secondary distribution system shall be interconnected as specified in (a), (b), or (c) below. (a) Metallic Interconnections. A metallic interconnection shall be made to the secondary grounded circuit conductor or the secondary circuit grounding conductor provided that, in addition to the direct grounding connection at the surge arrester: (1) The grounded conductor of the secondary has elsewhere a grounding connection to a continuous metal underground water piping system. However, in urban water-pipe areas where there are at least four waterpipe connections on the neutral and not fewer than four such connections in each mile of neutral, the metallic interconnection shall be permitted to be made to the secondary neutral with omission of the direct grounding connection at the surge arrester. (2) The grounded conductor of the secondary system is a part of a multiground neutral system of which the primary neutral has at least four ground connections in each mile of line in addition to a ground at each service. (b) Through Spark Gap or Device. Where the surge arrester grounding conductor is not connected as in (a) above or where the secondary is not grounded as in (a) above but is otherwise grounded as in Sections 250-81 and 250-83, an interconnection shall be made through a spark gap or listed device as follows: (1) For ungrounded or unigrounded primary systems, the spark gap or listed device shall have a 60-hertz breakdown voltage of at least twice the primary circuit voltage but not necessarily more than 10 kV, and there shall be at least one other ground on the grounded conductor of the secondary not less than 20 feet (6.1 m) distant from the surge arrester grounding electrode. (2) For multigrounded neutral primary systems, the spark gap or listed device shall have a 60-hertz breakdown or not more than 3 kV, and there shall be at least one other ground on the grounded conductor of the secondary not less than 20 feet (6.1 m) distant from the surge arrester grounding electrode. (c) By Special Permission. An interconnection of the surge arrester ground and the secondary neutral, other than as provided in (a) or (b) above, shall be permitted to be made only by special permission. 280-25. Grounding. Except as indicated in this article, surge arrester grounding connections shall be made as specified in Article 250. Grounding conductors shall not be run in metal enclosures unless bonded to both ends of such enclosure. 70-143 Chapter 3. Wiring Methods and Materials