In order for maintenance of SPD to be effective, components must be:

For effective maintenance of Surge Protective Devices (SPDs), it is essential that the components are accessible for periodic inspections. This accessibility allows maintenance personnel to regularly check the condition of the devices, test their functionality, and ensure that they are operating properly. Regular inspections are critical in identifying any wear, damage, or degradation that could impact the SPD's performance during a surge event.

When SPDs are accessible, it facilitates timely maintenance actions, such as replacing components or performing necessary repairs, which ultimately enhances the reliability of the lightning protection system. Ensuring the components can be easily reached very much supports ongoing safety protocols and efficiency in maintenance routines, allowing for quick response to any issues that may arise.

The other options, while they may have their own merits in different contexts, do not prioritize the key aspect of accessibility that aids in the effective and timely maintenance of SPDs.