European designers work to this document from both directions, as a specification for the device they buy and as the source of the protection level they must achieve at each position in an installation. In practice the selection begins with the lightning risk assessment and the coordination rules for protective devices, which decide where a device is needed and what voltage protection level is acceptable there, and only then is a product chosen from those certified against this standard. The document supports that process by defining the characteristics that appear on a device datasheet and by prescribing the tests that establish them, including the behaviour of the disconnector that removes a failed device from service, which is the safety feature that distinguishes a compliant product from a component of unknown provenance. Certification is granted by recognised bodies across the member states, and the marking on the device records the parameters the standard requires.