The units have overcurrent protection on them. a 15KW has a 70 Amp breaker on it. The Guardian brand can have a 12 circuit pre packaged transfer switch with it, or you can get a whole panel transfer, in 100 or 200 amp configurations. They have started making them with main breakers in them, and are service rated. So, it depends on connected load, what the customer wants to run with the generator, and what kind they want(Brand, liquid or air cooled). Big price difference between the to, also the 15KW turns at 1800 istead of 3600, so noise can be a factor to the customer. the guardian line is very user friendly, but have had so cold starting issues. Onan is also a good quality brand, but very pricey.