1. Lightning Fundamentals · Page 2 of 6
Direct vs Indirect Strikes
Understand the difference between a direct hit and nearby induced surges.
Direct strike
A direct strike injects lightning current into a structure, lightning rod, mast, or incoming service. The energy can destroy poorly bonded systems and create extreme potential differences across the installation.
Indirect / nearby strike
Far more common for LV equipment damage is the nearby strike. Magnetic fields and earth potential rise induce high-voltage transients on cables even when the building itself is not hit.
Switching surges
Not all dangerous transients come from weather. Capacitor bank switching, fault clearing, and large motor starts also create steep-front overvoltages that SPDs must handle.
Protection implication
Type 1 SPDs address high-energy lightning current at the service entrance. Type 2 and Type 3 devices handle residual and induced surges closer to equipment.