SPD · Surge protective device
A surge-diverting device coordinated in stages from service entrance to equipment, keeping lightning and switching transients off sensitive electronics.
Current numbers
UL 1449 5th Ed.current North American SPD product standard (UL 1449 Ed. 5, 2021; ANSI-approved revision 2025-10-21); NEC requires listed SPDs
10/350 µsType 1 / Class I SPD test waveform (direct-lightning current); Type 2 / Class II uses 8/20 µs