This part of IEC 61400 specifies essential design requirements to ensure the structural integrity of wind turbines. Its purpose is to provide an appropriate level of protection against damage from all hazards during the planned lifetime. This standard is concerned with all subsystems of wind turbines such as control and protection mechanisms, internal electrical systems, mechanical systems and support structures. This standard applies to wind turbines of all sizes. For small wind turbines IEC 61400-2 may be applied. IEC 61400-3-1 provides additional requirements to offshore wind turbine installations. This standard should be used together with the appropriate IEC and ISO standards mentioned in Clause 2.