Surge Protection Devices (SPD) in a DC Distribution Panel are a core resilience measure for protecting rectifier outputs, battery strings, photovoltaic DC buses, telecom loads, PLC power supplies, and sensitive instrumentation against transient overvoltages from. Surge Protection Devices (SPD) in a DC Distribution Panel are a core resilience measure for protecting rectifier outputs, battery strings, photovoltaic DC buses, telecom loads, PLC power supplies, and sensitive instrumentation against transient overvoltages from. Industrial surge protection explained — what causes surges, how SPDs work, the types and classes, and protecting PLCs, I/O, and signal lines from transients. 12 lessons, 8 dialects, no install — runs in your browser. What Are Surges and Transients? What Is an SPD and How Does It Work? Industrial. Siemens industrial surge protection devices help safeguard your electrical infrastructure from damaging surges and voltage spikes. Depending on the application and protection. Surge Protection Devices (SPD) selection, integration, and best practices for DC Distribution Panel assemblies compliant with IEC 61439. In addition, there are about 25 million lightning strikes in the US each year that cause between $650M to $1B in losses according to the Insurance Information.