Based on UL 1449:2021 Ed.5 (Surge Protective Devices)
A: The 5th Edition defines six categories, based on installation location and component completeness：

  • Type 1 (Listed, field-installable): Permanently connected SPDs for installation between the service transformer and the line side of the main service overcurrent device, or anywhere downstream. Includes watt-hour meter socket types and Molded Case SPDs that do not require external overcurrent protection.

  • Type 2 (Listed, field-installable): Permanently connected SPDs for installation on the load side of the main service overcurrent device, including branch panels and Molded Case SPDs. May require external overcurrent protection per listing.

  • Type 3 (Listed, field-installable): Point-of-utilization SPDs. Typically cord-connected, direct plug-in, or receptacle types. Must be installed at least 10 meters (30 feet) from the service panel (conductor length exclusive of SPD leads).

  • Type 1, 2, 3 Component Assemblies (Recognized Component, NOT field-installable): These are Type 4 component assemblies with integral or external short circuit protection. They have passed safety failure tests but have conditions of acceptability (e.g., exposed terminals) requiring factory installation inside listed equipment.

  • Type 4 Component Assemblies (Recognized Component, NOT field-installable): An assembly of one or more Type 5 components with a disconnector (integral or external) or means to comply with limited current tests. Incomplete as an SPD; requires further evaluation.

  • Type 5 (Recognized Component, NOT field-installable): Discrete components (e.g., MOVs, GDTs) that may be mounted on a PCB or provided in an enclosure. The building blocks of SPDs; incomplete and require full evaluation.