Virginia Fuel Gas CodeĀ section 616.1 sends the installer to NFPA 37.
NFPA 37 chapter 5 section 5.1.3 requires Approved mettalic flexible connectors shall be approved for protection against damage caused by settlement, vibration, expansion, contraction, or corrosion.Definition of approved (Acceptable to the authority having jurisdiction).
May want to check the CSST MFG specs, Wardflex requires an outdoor flexible connector on pad mounted appliances. Although not specifically mentioning generators, these appliances don’t vibrate close to a combustible engine.
Also, Wardflex states clearly, there product is not to be used as a connector for movable appliances.
Thank you,
Bob Orr
Building Official
Culpeper County