Exit sign logic

[Dex232]

Hello, I am looking for some help on understanding exit signs with emergency lighting on an emergency circuit. I am familiar with how battery powered exit signs with emergency lights function with no emergency circuit, they just run on battery power once main power is lost. But if I wanted to run an exit sign with emergency lights attached to main power and an emergency circuit so that the emergency lights turn on when main power is off but keep the emergency lights on when backup power is supplied is there a name for that behavior? I have heard the term "hot leg sensing" but could not find an exit sign that used this term to describe it.

Can any exit sign itself have this behavior or does it require outside logic with a relay?

I was looking to use Lithonia's LHQM series exit signs.

 

[d0nut]

That particular combo exit sign/emergency light has a battery in it. It isn't made to be fed from an emergency source like you are trying to do. If you have an emergency source, use the building lighting as your emergency lighting through a UL 924 or 1008 relay. There isn't a reason to use combo units or emergency unit equipment if you have an emergency source.

 

[Dex232]

That particular combo exit sign/emergency light has a battery in it. It isn't made to be fed from an emergency source like you are trying to do. If you have an emergency source, use the building lighting as your emergency lighting through a UL 924 or 1008 relay. There isn't a reason to use combo units or emergency unit equipment if you have an emergency source.

Thank you for the clarification.

 

[garbo]

Was never 100% sure on Exit & emergency lights. Back in the 1970's Philly had maybe a 40 page amendment to the NEC. Stated that only 12 volt WET cell batteries were only allowed to power them but every new fast food restaurant had the cheapest 6 volt types. At a large rich hospital that I retired from they only had battery back up short life Bodine battery pack ballast that were only in OR'S & five 13,200 volt switchgear rooms. Between having dual services with automatic tie breakers and 7 large generators supplying emergency power thru got away with not having to use battery backup exit lights. Now with LED'D batteries are tiny in these units . They put the cheapest 6 volt emergency lite packs in two generator rooms and they never lasted more then 3 years.