The 3GPP Rel-16 5G System focuses on enabling support for Industrial Internet of Things (IIoT) for Industry 4.0. Building blocks of 5G supporting use cases and requirements from the manufacturing sector are extreme mobile broadband, massive machine-type communication, ultra-reliable critical machine communication, non-public networks, time sensitive communication, 5G LAN communication, precise positioning. While for all of them, security plays an important role, the focus of this paper is on the 3GPP Rel-16 architecture and security concept of 5GS Non-Public Networks.We conclude with insights on the challenges for using 5G in the Operational Technology Industry.