NFPA 13, 2016 Edition, Section 7.1.2.1 Unless the requirements of 7.1.2.2 are met, a wet pipe system shall be provided with a listed relief valve not less than 1⁄2 in. (15 mm) in size and set to operate at 175 psi (12 bar) or 10 psi (0.7 bar) in excess of the maximum system pressure, whichever is greater.