1. Lightning Fundamentals · Page 3 of 6
Lightning Current Waveforms
10/350 µs and 8/20 µs waveshapes and what they mean for SPD ratings.
Standard test waves
Standards use standardized impulse shapes so products can be compared. Two shapes dominate LV SPD discussion:
- 10/350 µs: used to represent partial lightning current for Class I / Type 1 testing (Iimp)
- 8/20 µs: used for induced / residual surge current testing (In, Imax) for Type 2 devices
Reading a datasheet
When you see Iimp on a Type 1 SPD, think "can divert a portion of lightning impulse current." When you see In / Imax on a Type 2 SPD, think "repeated surge withstand for secondary protection."
Rise time matters
Faster fronts create higher inductive voltage drops on long leads. That is why installation geometry is as important as the SPD rating itself.