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An overview of the differences of Type I and Type II Surge Protection
Per the National Electrical CodeŽ (NEC) and ANSI/UL 1449, SPDs are designated as follows:
Type 1: Permanently connected, intended for installation between the secondary of the service transformer and the line side of the service disconnect overcurrent device (service equipment). Their main purpose is to protect insulation levels of the electrical system against external surges caused by lightning or utility capacitor
bank switching.
Type 2: Permanently connected, intended for installation on the load side of the service disconnect overcurrent device (service equipment), including brand panel locations. Their main purpose is 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 SPDs installed at a minimum conductor length of 10 meters (30 feet) from the electrical service panel to the point-of-utilization. Examples include cord connected, direct plug-in and receptacle type SPD
Reference: https://www.nemasurge.org/what-is-spd/
