Low Voltage Surge Protective Devices

A low-voltage surge protective device (SPD) limits transient voltages by diverting or limiting surge current.

SPDs are a cost-effective solution to prevent downtime, improve system and data reliability, and eliminate equipment damage caused by transient voltages and surges for power and signal lines. They are suitable for any facility or load 1,000 volts and below.

An SPD is typically installed in a power distribution panel, process control system, communications system, or other heavy-duty industrial systems to protect against electrical surges and voltage spikes, including those caused by lightning. Scaled-down versions of these devices are sometimes installed in residential service entrance electrical panels.

Per the National Electrical Code® (NEC) and American National Standards Institute (ANSI) / Underwriters Laboratories (UL) Standard 1449, SPDs are designated as:

  • Type 1: Permanently connected to protect insulation levels of the electrical system against external surges caused by lightning or utility capacitor bank switching
  • Type 2: Permanently connected to protect the sensitive electronics and microprocessor-based loads against residual lightning energy, motor-generated surges, and other internally generated surge events
  • Type 3: Point-of-utilization devices that include cord-connected, direct plug-in, and receptacle-type SPDs

NEMA members provide education and outreach activities for commercial, industrial, and residential users through the NEMA Surge Protection Institute.

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