A typical trap primer is equipped with a vacuum breaker built into the unit, and are UPC/ASSE 1018 Listed. (See PPP PR 500, for example. Sorry, I can't get it to load as an attachment)This manufacturer states that these have been installed in thousands of locations in California.
I have been questioned on the legality of this installation by a local water purveyor, who states it violates 603.3.5. They want us to provide a complete air gap below the trap primer, in the wall. Please let me know whether you feel a listed trap primer installation is in compliance with the intent of the CPC for protection of the building’s potable water system.
The building is new, and is fully equipped with reduced-pressure backflow protection at the water entrance.