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Intermatic Support

Where Should I Wire My HVAC Surge Protective Device on a Disconnect?

Applies To

Intermatic hardwired surge protective devices (SPDs) used in HVAC applications, including the AG3000 Surge Protective Device and the CD1-024R COMPRESSOR DEFENDER®.

Question / Problem

Where should I wire my HVAC surge protective device on a disconnect?

Safety Warning

Warning: Risk of fire or electric shock. Disconnect power at the circuit breaker(s) or disconnect switch(es) before installing or servicing. Installation and service must be performed by a qualified licensed technician or electrician in accordance with National and Local Electrical Code requirements.

Answer

Intermatic recommends wiring the SPD on the load side of the HVAC disconnect. This allows a service technician to replace the SPD without needing access to the breaker panel.

Both line-side and load-side installation are permitted. The wiring location does not affect the performance of the surge protective device as long as the installation follows the requirements for the specific SPD type:

  • Type 1 SPDs are permanently connected SPDs intended for installation between the secondary of the service transformer and the line side of the service equipment overcurrent device, as well as the load side. This includes watt-hour meter socket enclosures and molded case SPDs that are intended to be installed without an external overcurrent protective device. (ANSI/UL 1449). 
  • Type 2 SPDs are permanently connected SPD intended for installation on the load side of the service disconnect overcurrent device, including SPDs located at the branch panel and molded case SPDs. (ANSI/UL 1449).
     

Tips / Additional Notes

  • The AG3000 and CD1-024R (COMPRESSOR DEFENDER) are designed for HVAC equipment protection. The CD1-024R includes additional compressor protection features beyond surge suppression.
  • Intermatic SPD lead wires are tinned copper. Keep lead lengths as short as possible; longer leads reduce surge protection effectiveness.
  • SPDs protect against transient voltage surges caused by utility switching, motor cycling and similar electrical events. They do not provide protection from direct lightning strikes.