Which medium is commonly used for short-range simple control networks within a building?

• A. Ethernet
• B. Coaxial
• C. Two-wire
• D. Shielded

Answer: (C)

For short-range, simple building control networks, a two-wire bus is the practical choice because it provides a straightforward, inexpensive way to connect sensors and actuators over a limited area. Two conductors can carry the control signals and, if needed, low power to devices along the same run, which keeps installation simple and cost-effective. This setup is well-suited for basic on/off or low-speed communication typical of building controls.

Ethernet, while powerful for data networks, is more complex and overkill for simple control tasks, requiring more hardware, topology planning, and longer distances. Coaxial cable is bulkier and less flexible for modern indoor control layouts and isn’t the common go-to for simple building control networks today. Shielded describes a protective feature of a cable (reducing EMI) rather than a distinct medium; it can be applied to various media, but the fundamental medium used for this purpose is two-wire.