ETC recommends ELTS2 cabinets be fed with a constant source of emergency power.
Imagine an ELTS2 fed with Normal power only. Normal power drops out, and the generator-fed Emergency power takes a few seconds to start up. How will the ELTS2 behave? Will it stay in Normal mode, or switch into Emergency mode?
- ELTS2 will lose power when Normal power drops out.
- The ELTS2 should boot on the application of Emergency power.
- It will detect the lack of Normal power, and switch into Emergency mode.
Having said that, most local codes have a time limit for lights to come back on in a power-loss situation (often 10 seconds or less). If the Emergency power startup and subsequent ELTS2 booting combined take longer than that limit, you could be held liable for a code violation. A constant Emergency power source is always preferable to an alternative.