According to NFPA 13-2010, what is the largest screwed union allowed?

The largest screwed union allowed, as per NFPA 13-2010, is indeed 2 inches. This standard outlines specific requirements for the design and installation of sprinkler systems, including the type and size of fittings that can be used.

Screwed unions are typically used in sprinkler systems to provide a means of connection that allows for disassembly without damage to the pipes. Having a standardized maximum size for these unions ensures compatibility with various system components and maintains the integrity of the sprinkler network. Allowing a maximum size of 2 inches helps minimize potential leakage points and aids in maintaining the system's overall reliability and performance.

Using unions larger than this limit, such as 3 inches or 4 inches, is not permitted under this section of the NFPA code, as larger screws may lead to complications during installation or maintenance, like misalignment or undue stress on the system. Therefore, adhering to the 2-inch maximum aligns with safety and operational guidelines in fire protection system installations.