How do the requirements in clause 5.4.11, which requires external circuits to be separated from earth in 'normal' pluggable equipment type A, apply to the shield of an external cable? Can the shield be connected to earth?
Per the IEC TR 62368-2 entry for 5.4.11, the original intent of these requirements was to prevent communication system workers outside the building from being injured if there was a fault inside the building between mains and earth and the equipment had an external circuit extending from it to an communications network outside the building. If communications workers were working on communications circuits outside the building they could be injured if adequate safeguards were not in place. Therefore, per 5.4.11 and Table 13 (of IEC 62368-1:2018), the requirement only applies to Table 13 ID No. 1.
In considering the requirement clause 5.4.11 of IEC 62368-1:2018, we need to remember that, an external circuit is a circuit external to (outside) the equipment, but not all external circuits extend outside the building.
Per your question, it is not clear if the subject circuit is an (a) an external circuit extending outside the building, thus obviously covered by Table 13 ID No. 1 (e.g., telecommunication circuit), or (b) an external circuit installed wholly within the same building structure (e.g., PoE).
If (a), and the installation instructions / instructional safeguards require that the shield is to be connected to protective earth at the equipment and outside the building, the shield would be part of the protective earthing scheme. However, if the shield is connected to protective earth through the equipment, the equipment shall meet either the 4 dashed paragraph in 18.104.22.168.
If (a), and the installation instructions do not require the shield to be connected to protective earth, then the shield should be considered similarly to the other external circuits extending outside the building.
If (b), and the external circuit is “installed wholly within the same building structure” (see first condition to Table 13), then the cable is not a true ID No. 1, and the current view is that 5.4.11 requirements are not applicable. (There is no indication in IEC TR 62368-2 that the intent of IEC TC108 was to extend the application of 5.4.11 to PoE and other external circuits wholly inside the building that may utilize paired / twisted pair conductors.)
IEC TC108 considers this area of the standard and the relationship of 22.214.171.124.2.4 / Table 13 with “IEC TR 62102, Electrical safety - Classification of interfaces for equipment to be connected to information and communications technology networks,” as an area in 62368-1 needing more work. Therefore, an Ad Hoc Group is working on proposals that may greatly affect IEC TR 62102 and Table 13, which should provide some additional clarity to this requirement in the future.