IEC 60364-5-53 deals with general requirements for isolation, switching and control and with the requirements for selection and erection of the devices provided to fulfil such functions. Clause 534 contains provisions for the application of voltage limitation in order to obtain insulation coordination in the cases described in HD 60364-4-44, EN 60664-1, EN 62305-1, EN 62305-4 and CLC/TS 61643-12. Clause 534 focuses mainly on the requirements for the selection and erection of SPDs for protection against transient overvoltages where required by IEC 60364-4-44:2007, Clause 443, the EN 62305 series, or as otherwise specified. Clause 534 does not take into account: - surge protective components which may be incorporated in the appliances connected to the installation; - portable SPDs NOTE – Further information can be found in CLC/TS 61643-12. Clause 534 applies to a.c. power circuits. As far as it is applicable, the requirements of this clause may be followed for d.c. power circuits.