White Paper

Powering Safety Systems - Significant Power 'Headroom' Is Good Practice

Source: Emerson
EPM

One of the most common sources of Fire and Gas detection system failure is power supply interruption and disturbance. Power supply specifications of an instrument refer to the voltage that must appear at the instrument power terminals, not the power supply rated output. There are many factors that impact voltage reaching the fire or gas detector, any one of which may cause an unwanted shutdown or damage to the instrument.

The most fundamental factor to consider is wire resistance between the power supply and the device but there many other factors.