Skip to main content

Search

Intermatic Support

What Is the Difference Between a Type 1 and Type 2 Surge Protective Device?

Applies To

All Intermatic surge protective devices (SPDs).

Question / Problem

What is the difference between a Type 1 and a Type 2 surge protective device?

Answer

The type designation refers to where the SPD is permitted to be installed relative to the main service overcurrent protective device (main breaker), as defined by UL 1449 and the National Electrical Code (NEC):

  • Type 1 SPDs are permitted on either the line side (before) or the load side (after) the main service overcurrent protective device. A Type 1 SPD does not require a separate breaker ahead of it.
  • Type 2 SPDs are permitted on the load side (after) the main service overcurrent protective device only. When a Type 2 SPD is connected at a panel, it requires an independent breaker dedicated to the SPD circuit.

In practice, a Type 1 SPD can be installed on either the line side or the load side of the main service overcurrent protective device, so it can be used in any location where a Type 2 SPD would be used. A Type 2 SPD must always be installed on the load side of the main service overcurrent protective device.

Many Intermatic SPDs are dual-rated as both Type 1 and Type 2. Always confirm the type rating for your specific model before installation.

Tips / Additional Notes

  • The UL certification and type rating for each Intermatic SPD is listed on the technical data sheet and on the product label.