According to NEC Section 358.28(B), what should not be threaded?

The correct choice emphasizes that Electrical Metallic Tubing (EMT) should not be threaded according to the National Electrical Code (NEC) Section 358.28(B). EMT is designed for making stub-ups, providing electrical protection, and facilitating circuit installations. The reasoning behind this regulation is that threading EMT can compromise the integrity of the tubing, in terms of both its structure and electrical continuity, which is crucial for safety and performance.

Moreover, threading EMT is also not practical because it is typically used in applications where fittings are designed to connect without the need for threading. The use of compression or set-screw type fittings is common, helping to ensure a reliable connection without the risks associated with threading.

The other types of conduits, such as rigid nonmetallic conduit (RNC), rigid metal conduit (RMC), and flexible conduit, can be threaded according to their respective specifications and intended uses. Each of these types of conduit has different requirements and design features that accommodate threading, thereby allowing for versatility in electrical installations.