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Section 5.2.5

NLSI Recommendations for Surge Protection Devices

By Richard Kithil, President & CEO, NLSI

  1. The Problem. According to recent NEETRAC (1) and other testing, many surge protection devices (SPD) have failed to perform according to ANSI, IEEE, UL, IEC or other required specifications. How can the concerned applications user be assured that this equipment will perform satisfactorily under abnormal power quality conditions?
  2. We provide this generalized reference guideline for selecting appropriate power and data/signal devices.

  3. How SPDs work. If a transient suddenly is imposed upon an electrical system, there are several methods of defense responsiveness: protection by open circuit or protection by short circuit. Voltage breakdown devices (gas discharge tubes and spark gaps), voltage limiting devices (metal oxide varistors or avalanche diodes), bandwidth suppressors (various filters, inductors and capacitors), and isolation devices (opto-isolators and fibre-optics) are the principle technologies employed. Each type of SPD has various advantages and disadvantages.

Hybrid SPDs incorporating some combinations of the above technologies are more costly but more beneficial in handing different transient waveform components. Purchasing SPDs based solely upon cost is a (costly) mistake.

  1. General Requirements. Per IEEE, SPDs shall be installed at designated Cat. C main panels, at appropriate Cat. B secondary feeder panels, and at Cat A plug-in outlets as necessary. All power, data and signal lines entering or leaving the structure should be considered carefully for surge protection. (See IEEE 1100, below, for more details.)
  2. SPDs must limit peak let-through voltages to below equipment vulnerability levels. Three way protection of Phase to Neutral, Phase to Ground, and Neutral to Ground must be standard. SPDs should have diagnostic signaling audible and visual is preferred to indicate status condition. If internal modules within the SPD are subject to degradation and/or failure, they should be replaceable. Manufacturers must provide clear, detailed installation instructions (short leads and twisted cables are essential to reduce impedance and magnetic effects).

    SPDs shall not interfere or restrict normal power quality. They shall not corrupt incoming power; shall not interrupt the power supply during operation; shall not have excessive current leakage to ground.

  3. Conformance to Quality and Testing Standards. In order to distinguish reputable from not-so-reputable products, we suggest selection of the SPD be based upon:
    • Conformance to UL 1449 Second Edition Testing. An optional part of UL 1449SE is called Adjunct Endurance Testing. Performance characteristics are rated according to three Grades - Classes - Modes.

      • GRADES = Type of applied surge: Grade A 6000V and 3000A (this is called for by IEEE 62.41); Grade B 4000V and 2000A; Grade C 2000V and 1000A.
      • CLASSES = Type of let-through-voltage: Class I = 330V; Class II = 400V; Class III = 500V.
      • MODES = Mode 1 does not contaminate ground; Mode 2 does contaminate ground.
    • Conformance to all relevant IEEE and IEC Standards.
    • Conformance to the Federal Commercial Description (CID). This is similar to the UL1449SE Adjunct Endurance Testing. Federal purchasing agents can request the CID of an SPD and be assured of known, tested and guaranteed performance results.
    • Manufacturer compliance with ISO 9000/9001 Quality Control procedures.

References and Further Reading

  1. NEETRAC National Electric Energy Testing, Research, and Applications Center, Atlanta GA. WWW:
  2. Standler, R.B., Protection of Electronic Circuits from Overvoltages, John Wiley, NY, 1989.
  3. IEEE Std. 1100-1999, Powering and Grounding Sensitive Electronic Equipment, IEEE, NY, 1995.

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