Question

According to NFPA 99, what is the maximum allowable voltage drop from the emergency generator to the life safety branch transfer switch?

Accepted Answer

According to NFPA 99, Health Care Facilities Code, the maximum allowable voltage drop from the emergency generator to the life safety branch transfer switch under full load conditions is 5%. The life safety branch is a critical subset of the essential electrical system that powers equipment necessary for life safety, such as emergency lighting, fire alarm systems, and egress routes. A transfer switch automatically switches the load from the normal power source to the emergency generator when normal power is lost. The 5% voltage drop limit ensures that equipment connected to the life safety branch receives sufficient voltage to operate reliably during an emergency. Exceeding this voltage drop can cause equipment malfunctions, reduced performance, or even failure. This limit applies to the combined voltage drop in the feeder and branch circuit conductors from the generator output terminals to the transfer switch input terminals. The NEC (National Electrical Code) also has requirements, but in healthcare NFPA 99 is the governing standard.

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According to NFPA 99, what is the maximum allowable voltage drop from the emergency generator to the life safety branch transfer switch?

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