ITU-T K.21 PDF

This Recommendation specifies resistibility requirements and test procedures for telecommunication equipment that is attached to or installed within a customers' premises. The requirements of this Recommendation assume that earthing and bonding is in accordance with [ITU-T K.66].

The types of equipment covered by this Recommendation include all types of telecommunication equipment, e.g., modems, telephones, routers, implementations of digital subscriber lines and personal computers. NOTE – Associated equipment containing ports with a low surge impedance to earth connected by short cables, e.g., printers using universal serial bus (USB) cables, may be susceptible to damage due to circulating earth currents. Refer to [ITU-T K.66] and [b-ITU-T K.85] for methods of protection.

This Recommendation applies to both external and internal ports. [ITU-T K.44], covering basic test methods and test circuits, is an integral part of this Recommendation. This Recommendation should be read in conjunction with [ITU-T K.11] and [ITU-T K.39].