NEC 445.12 includes the overcurrent protection requirements for generators. Conductor protection is located in 445.13 (B) and that protective device may or may not be the same as the generator protection. The overcurrent protective device for constant-voltage generators is only required to provide overload protection. Keeping in mind that generators are not required to be listed (which eliminates dependence on the product standard) how would a designer, installer, AHJ or owner know the overcurrent device selected would provide adequate overload protection? For transformers, 450.3 provides maximum ratings or settings of the overcurrent device to ensure equipment protection.