A Type 1/Class I device should be fitted at the incoming supply of any building fitted with a steel frame or Lightning Protection System (Faraday Cage), where power is supplied by overhead cables or where the building is in a remote area.
The Type 1 SPD protects electrical installations against the catastrophic effects of a direct lightning strike. Where a Type 1 SPD is fitted at the incoming supply, Type 2 protection 'downstream' may be required to protect distribution boards and sensitive electrical equipment from damage caused by let-through voltage.
Type 1 SPD is characterized by a 10/350 µs current wave.