Article 285

Surge-Protective Devices (SPDs), 1000 Volts or Less

Part I. General

285.1 Scope. This article covers general requirements, instal‐ lation requirements, and connection requirements for surge- protective devices (SPDs) permanently installed on premises wiring systems of 1000 volts or less.

Informational Note: Surge arresters 1000 volts or less are also known as Type 1 SPDs.

  1. Uses Not Permitted. An SPD device shall not be instal‐ led in the following:
    1. Circuits over 1000 volts
    2. On ungrounded systems, impedance grounded systems, or corner grounded delta systems unless listed specifically for use on these systems
    3. Where the rating of the SPD is less than the maximum continuous phase-to-ground voltage at the power frequency available at the point of application
  2. Number Required. Where used at a point on a circuit, the SPD shall be connected to each ungrounded conductor.
  1. Listing. An SPD shall be a listed device.
  2. Short-Circuit Current Rating. The SPD shall be marked with a short-circuit current rating and shall not be installed at a


point on the system where the available fault current is in excess of that rating. This marking requirement shall not apply to receptacles.

Part II. Installation

  1. Location. SPDs shall be permitted to be located indoors or outdoors and shall be made inaccessible to unquali‐ fied persons, unless listed for installation in accessible loca‐ tions.
  2. Routing of Connections. The conductors used to connect the SPD to the line or bus and to ground shall not be any longer than necessary and shall avoid unnecessary bends.
  3. Type 4 and Other Component Type SPDs. Type 4 component assemblies and other component type SPDs shall only be installed by the equipment manufacturer.

Part III. Connecting SPDs

285.21 Connection. Where an SPD device is installed, it shall comply with 285.23 through 285.28.

  1. Type 1 SPDs. Type 1 SPDs shall be installed in accord‐ ance with 285.23(A) and (B).
    1. Installation. Type 1 SPDs shall be installed as follows:
      1. Type 1 SPDs shall be permitted to be connected to the supply side of the service disconnect as permitted in 230.82(4), or
      2. Type 1 SPDs shall be permitted to be connected as speci‐ fied in 285.24.
    2. At the Service. When installed at services, Type 1 SPDs shall be connected to one of the following:
    1. Grounded service conductor
    2. Grounding electrode conductor
    3. Grounding electrode for the service
    4. Equipment grounding terminal in the service equipment
  2. Type 2 SPDs. Type 2 SPDs shall be installed in accord‐ ance with 285.24(A) through (C).
    1. Service-Supplied Building or Structure. Type 2 SPDs shall be connected anywhere on the load side of a service disconnect overcurrent device required in 230.91, unless installed in accordance with 230.82(8).
    2. Feeder-Supplied Building or Structure. Type 2 SPDs shall be connected at the building or structure anywhere on the load side of the first overcurrent device at the building or structure.
    3. Separately Derived System. The SPD shall be connected on the load side of the first overcurrent device in a separately derived system.
  3. Type 3 SPDs. Type 3 SPDs shall be permitted to be installed on the load side of branch-circuit overcurrent protec‐ tion up to the equipment served. If included in the manufac‐ turer’s instructions, the Type 3 SPD connection shall be a minimum 10 m (30 ft) of conductor distance from the service or separately derived system disconnect.
  4. Conductor Size. Line and grounding conductors shall not be smaller than 14 AWG copper or 12 AWG aluminum.
  5. Connection Between Conductors. An SPD shall be permitted to be connected between any two conductors — ungrounded conductor(s), grounded conductor, equipment grounding conductor, or grounding electrode conductor. The grounded conductor and the equipment grounding conductor shall be interconnected only by the normal operation of the SPD during a surge.
  6. Grounding Electrode Conductor Connections and Enclosures. Except as indicated in this article, SPD grounding connections shall be made as specified in Article 250, Part III. Grounding electrode conductors installed in metal enclosures shall comply with 250.64(E).


Chapter 3 Wiring Methods and Materials