Each direct-buried single conductor cable shall be located ______ in the trench to the other single conductor cables in the same parallel set of conductors, including equipment grounding conductors.

In the context of direct-buried single conductor cables, the requirement for them to be located "in close proximity" to one another and to equipment grounding conductors is important for several reasons. Maintaining a close proximity aids in reducing inductive coupling and helps ensure that the conductors are able to function effectively as a cohesive system without significant interference.

When conductors are grouped closely together, it can facilitate proper voltage distribution and help mitigate the effects of electromagnetic interference, which may arise when conductors are spaced too far apart. Proper spacing is also crucial for reasons of safety and operational reliability, especially when considering factors like physical protection from environmental elements and mechanical damage.

In contrast, options like perpendicular orientation or bundling together don't align with the best practices and standards for installations that involve direct-buried conductors. Additionally, spacing too far apart (spaced apart) could hinder performance and safety, making it less effective for installations where conductors must operate efficiently and safely in close proximity. Therefore, specifying that cables be located in close proximity accurately reflects the standards that prioritize effective performance and safety in wiring methods.