Series vs. Parallel Surge Protection

When designing and installing power distribution systems, engineers and contractors must select surge protective devices (SPDs) to protect electrical equipment and systems from transient overvoltages. To do so, engineers and contractors must understand the differences between parallel-connected and series-connected SPDs, and where to best apply each type of device. The following narrative summarizes the design and function of parallel-connected and series-connected SPDs, and describes some common applications for each.

Proper application first requires an understanding of the purpose of each type of device and how they are connected to a power distribution system. In general, a parallel-connected device is installed on the load side of a service panel, typically to a dedicated circuit breaker. Alternatively, standalone series-connected filters are connected in-line near protected load equipment.