Surge Arresters, Over 1000 Volts
Part I. General
280.1 Scope. This article covers general requirements, instal‐ lation requirements, and connection requirements for surge arresters installed on premises wiring systems over 1000 volts.
- Number Required. Where used at a point on a circuit, asurge arrester shall be connected to each ungrounded conduc‐ tor. A single installation of such surge arresters shall be permit‐ ted to protect a number of interconnected circuits, if no circuit is exposed to surges while disconnected from the surge arrest‐ ers.
- Surge Arrester Selection. The surge arresters shall comply with 280.4(A) and (B).
- Rating. The rating of a surge arrester shall be equal to or greater than the maximum continuous operating voltage avail‐ able at the point of application.
- Solidly Grounded Systems. The maximum continuous operating voltage shall be the phase-to-ground voltage of the system.
- Impedance or Ungrounded System. The maximum continuous operating voltage shall be the phase-to-phase volt‐ age of the system.
- Silicon Carbide Types. The rating of a silicon carbide-type surge arrester shall be not less than 125 percent of the rating specified in 280.4(A).Informational Note No. 1: For further information on surge arresters, see IEEE C62.11-2012, Standard for Metal-Oxide Surge Arresters for Alternating-Current Power Circuits (>1 kV); and IEEE C62.22-2009, Guide for the Application of Metal-Oxide Surge Arresters for Alternating-Current Systems.Informational Note 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,280.11 ARTICLE 285 — SURGE-PROTECTIVE DEVICES (SPDS), 1000 VOLTS OR LESS
and other causes. See the manufacturer’s application rules for selection of the specific arrester to be used at a particular loca‐ tion.
Part II. Installation
- Location. Surge arresters shall be permitted to be located indoors or outdoors. Surge arresters shall be made inaccessible to unqualified persons, unless listed for installation in accessible locations.N
- Uses Not Permitted. A surge arrester shall not be installed where the rating of the surge arrester is less than the maximum continuous phase-to-ground voltage at the power frequency available at the point of application.
Part III. Connecting Surge Arresters280.21 Connection. The arrester shall be connected to one of the following:
- Grounded service conductor
- Grounding electrode conductor
- Grounding electrode for the service
- Equipment grounding terminal in the service equipment
- Surge-Arrester Conductors. The conductor between the surge arrester and the line and the surge arrester and the grounding connection shall not be smaller than 6 AWG copper or aluminum.
- Interconnections. The surge arrester protecting a transformer that supplies a secondary distribution system shall be interconnected as specified in 280.24(A), (B), or (C).
- Metal Interconnections. A metal interconnection shall be made to the secondary grounded circuit conductor or the secondary circuit grounding electrode conductor, if, in addi‐ tion to the direct grounding connection at the surge arrester, the following occurs:
- Additional Grounding Connection. The grounded conductor of the secondary has elsewhere a grounding connec‐ tion to a continuous metal underground water piping system. In urban water-pipe areas where there are at least four water- pipe connections on the neutral conductor and not fewer than four such connections in each mile of neutral conductor, the metal interconnection shall be permitted to be made to the secondary neutral conductor with omission of the direct grounding connection at the surge arrester.
- Multigrounded Neutral System Connection. The groun‐ ded conductor of the secondary system is a part of a multi‐ grounded neutral system or static wire of which the primary neutral conductor or static wire has at least four grounding connections in each 1.6 km (1 mile) of line in addition to a grounding connection at each service.
- Through Spark Gap or Device. Where the surge arrester grounding electrode conductor is not connected as in 280.24(A), or where the secondary is not grounded as in 280.24(A) but is otherwise grounded as in 250.52, an intercon‐nection shall be made through a spark gap or listed device as required by 280.24(B)(1) or (B)(2).
- Ungrounded or Unigrounded Primary System. For ungrounded or unigrounded primary systems, the spark gap or listed device shall have a 60-Hz 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 that is not less than6.0 m (20 ft) distant from the surge-arrester grounding elec‐ trode.
- Multigrounded Neutral Primary System. For multigroun‐ ded neutral primary systems, the spark gap or listed device shall have a 60-Hz breakdown of not more than 3 kV, and there shall be at least one other ground on the grounded conductor of the secondary that is not less than 6.0 m (20 ft) distant from the surge-arrester grounding electrode.
- By Special Permission. An interconnection of the surge- arrester ground and the secondary neutral conductor, other than as provided in 280.24(A) or (B), shall be permitted to be made only by special permission.
280.25 Grounding Electrode Conductor Connections and Enclosures. Except as indicated in this article, surge-arrester grounding electrode conductor connections shall be made as specified in Article 250, Parts III and X. Grounding electrode conductors installed in metal enclosures shall comply with 250.64(E).