Generac Standby 6438 Manuel De L'utilisateur page 8

+ If this generator is used to power electrical load circuits normally powered by a utility power source, it is required
by code to install a transfer switch. The transfer switch must effectively isolate the electrical system from the utility
distribution system when the generator is operating (NEC 702). Failure to isolate an electrical system by such
means will result in damage to the generator and also may result in injury or death to utility power workers due to
backfeed of electrical energy.
4 Automatic Standby Generator Owner's Manual