According to the ANSI/UL 1449 5th Edition, the installation location differentiates Type 1 and Type 2 SPDs:
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Type 1 SPD: Designed for installation between the secondary of the service transformer and the line side of the service equipment overcurrent device. This includes the meter socket or the main breaker’s line side. They are intended to be installed without an external overcurrent protective device and have a very high capacity, capable of handling a portion of a direct lightning strike.
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Type 2 SPD: Designed for installation on the load side of the service equipment overcurrent device. This is the most common location, at the output of the main breaker in the main distribution panel or in sub-panels, protecting downstream branch circuits.
Selection Advice:
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Choose Type 1 if your application requires the highest level of safety and withstand capability, such as when replacing an old SPD in the meter socket or when concerned about direct lightning strikes on the service entrance.
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For the vast majority of new installations or retrofits, installing the SPD after the main breaker (Type 2) is the standard and most common practice.
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Many Prosurge series (e.g., PSP C, HPSP, PS, 20PSP, PSP B) are dual-certified as both Type 1 and Type 2, offering maximum installation flexibility.