This Recommendation: o provides recommendations for bonding and earthing of telecommunication equipment in residential and commercial customer premises; o refers to [ITU-T K.21] for equipment resistibility requirements; o recommends earthing and bonding requirements to coordinate with the resistibility requirements of [ITU-T K.21] and the safety requirements of [IEC 60950-1] and [IEC 62368].; o recommends the installation practices for bonding of all services and the installation of SPDs; o illustrates problems associated with earthing and bonding and provides solutions for these earthing and bonding problems. These include: 1) methods to improve the earthing and bonding; 2) methods of providing additional protection external to the equipment; 3) special resistibility and safety requirements; o recommends responsibilities for protection at customer premises; o refers to [IEC 62305-3] for protection against direct lightning. This revision of K.66 includes an update of the references and a revision of section 6.3 to include more information on preventing equipment damage. Appendix IV, containing information on Special resistibility requirements has been deleted. The reader is directed to [ITU-T K.44].