definitions of electrical equipment, includes wiring systems (a cable and parts which secure and enclose it)I seriously doubt that the 'dead end' termination of an unused cable in a JB qualifies as that (per Part 2 definitions).
So I would say it does qualify
Yes 513.1 requires it!Whatever, I still contend that the common-sense view should prevail. Can you think of any (electrical) reason why the end of an usused cable needs to be accessible?