Surge protection for use in low-voltage supplies. The SPD II series is tested according to UL 1449 ed. 3 (file E354261) as type 4 for use in type 2 applications. These arresters are used in mains voltages up to 550 V L-PEN, installed according to the mains system specifications and are able to discharge a rated current of up to 50 kA (8/20 µs) per path. The SPD II has a compact, modular structure and a standard module width of 17.8 mm; it allows rapid and simple exchange of the arrester. This spare arrester allows re-activation of the SPD II 550 V protection after failure.