Generators are commonly installed for buildings or structures requiring emergency systems, legally required standby systems or optional standby power systems. Some generators are located within the building or structure they supply; but, frequently, they are located outside.
Jim Dollard has an extensive background in codes and standards. If you have a query about the National Electrical Code (NEC), Jim will help you solve it. Questions can be sent to firstname.lastname@example.org. Answers are based on the 2014 NEC. Previous use of gray conductors