Many helicopters and fixed wing aircraft currently in operation have overvoltage protection relays to protect their aircraft systems from being damaged by high voltages from external GPUs. There are several fixed-wing aircraft and helicopters that have lower overvoltage protection relay settings set to 29–29.5V. The majority of general aviation or business aircraft have their overvoltage protection relays set to 30 to 31 volts, and these aircraft can tolerate a true 28V starting unit. Some GPUs can range from 28 to 31 volts, depending on the brand and their age. A 28 volt battery pack, such as the START PAC® 6028QC™, will actually read 30.5–31 volts when fully charged. One example of an aircraft where the voltage protection relay is set at an unusually low value, is the Eclipse 500 at 29 volts. At many airport facilities, the GPUs exceed this value.