Provides a range of tests which may be required for protective coverings consisting of extruded oversheaths when the coverings, in addition to protecting underlying metallic layers against corrosion, are required to fulfil special functions, for the following types a) and b), such as: a) insulated sheath systems: i) where special bonding is employed to reduce sheath losses, resulting in a sheath voltage under full load conditions, ii) where the cable sheath can be isolated from earth to permit a voltage to be applied to the oversheath to check the integrity of the covering. b) uninsulated sheath system: i) protection against corrosion of the underlying metal layer where preservation of the metal layer is of particular importance and/or the combination of the particular metal and the cable environment would give rise to a serious risk of corrosion. These tests are only appropriate to particular conditions and use, and do not have to be implemented for normal conditions and use. Guidance on their implementation will be provided in the relevant cable specification.