Interpretation #6595

The question does not state if this is a legally required system or not. It appears to state an emergency "system" is installed with completely separate wiring systems with no connection to each other and yet does not state if an automatic transfer switch is installed or if the generator will pick up any loads within the required 10 seconds. Other issues may also need to be addressed, including occupancy and load. An emergency power system is generally designed and supplied by both normal and generator power. In some cases, it is relay controlled to transfer power from a normal source to an emergency source using a transfer switch. If normal power is lost, a generator will feed the emergency system through the automatic transfer switch. The code does not generally intend to require three different sources of power. Additionally, a DEC statement that was issued by the State Fire Marshal a few years ago specifically allows this condition in a specific case. Further, if half the lights are on "normal" power and half are on "emergency," no one manual act could leave the path of egress in darkness, because the distributions are separate all the way to the source of supply. If the source of supply fails, the generator kicks in. While the question is based in the building volume, careful reading of the documentation indicates the NEC allows an alternate (second) power source from the utility if it is deemed reliable. If only the standard utility source is used, a battery backup system would be required. If a generator capable of picking up the load within 10 seconds and tested in accordance with the governing documents is used, the code allows that as it is not depending on the power company. The building code commentary provides reference to the utility and NEC requirements and the commentary does not disallow the generator.