What is the permitted maximum size of cast iron fittings where pressure is at 300 psi?

The correct choice regarding the permitted maximum size of cast iron fittings where pressure is at 300 psi is 2 inches. This specification is outlined in the NFPA 13 standards, which detail the types of materials and their limitations based on pressure ratings.

Cast iron fittings, due to their material properties, have defined pressure limits that ensure their safe and effective use in sprinkler systems. At higher pressures, the risks of failure increase, thus necessitating restrictions on the size of fittings depending on the pressure they will be subjected to.

When the pressure reaches 300 psi, it is essential to use fittings that can safely manage the stress without failure. The standard establishes a maximum of 2 inches for cast iron fittings under these conditions, balancing the need for structural integrity and safety with operational requirements.

This standard helps to prevent potential hazards that might arise from using incorrectly sized fittings under excessive pressure, ensuring the overall reliability and effectiveness of the sprinkler system in fire protection scenarios.