Siemens SIPROTEC 5 V7.80 Operation page 66

Handling of Plug-In Modules
4.1 Installation, Removal, Replacement
NOTE
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If you have not cabled the optical fiber plug-in modules, then seal the terminals with protective covers. This
prevents soiling of the terminals.
66 SIPROTEC 5, Operation, Manual
C53000-G5040-C003-9, Edition 06.2018