Exit lighting

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easymoney

Member
If you have two lighting circuits in a building, How do you wire exit lights so they only turn on if both circuits go out?
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
If you have two lighting circuits in a building, How do you wire exit lights so they only turn on if both circuits go out?
You don't.

If the general lighting goes out for any reason in area "A", you need emergency lighting to come on for that area. What if you had a fire in the building? How do people find their way out in the dark? "Wait, let me kill the lighting in the other half of the building so the e-lights come on". I'm thinking probably not.
 

easymoney

Member
Maybe I did not post my question correctly.
If I have I have 2 light curcuits in a area, If i shut off or lose one I do not need the emergency lights to go on because I have the other circuit on. I only want the emergency lights to go on if i lose both circuits
 

dicklaxt

Senior Member
I don't know how the Code reads but electrically, if you put a relay in parallel with the load in a circuit,it will drop out the relay closing one of its contacts on denergization,do this in each normal lighting circuit and then put the relay contacts in series in the emergency circuit.

dick
 

raberding

Senior Member
Location
Dayton, OH
Occupation
Consulting Engineer
emerg ltg

emerg ltg

NEC 700.12 describes the Source of Power requirements...if using Unit Equip (battery packs), the circuit needs to be the SAME CIRCUIT as that feeding the NORMAL lighting in the area
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
Maybe I did not post my question correctly.
If I have I have 2 light curcuits in a area, If i shut off or lose one I do not need the emergency lights to go on because I have the other circuit on. I only want the emergency lights to go on if i lose both circuits
So the lighting is set up like this?

A B A B A B A B
B A B A B A B A
A B A B A B A B

And it's open plan, with no closed offices or areas not covered by both circuits? If the answer to any of these is "no", then I think you still need to have the e-lights go on in the area affected, even if some light bleeds over from adjacent lighting or exterior windows.
 
your gonna have to decide which circuit you want the exits on. you cannot wire them in the manner you describe. you may split them between the two lighting circuits but to have one circuit fail and the other still energized without activating your device is not gonna happen unless the device is on the failed circuit.
 

TNGuy81

Member
Location
Nashville TN
you got to have them on a circuit thats constantly hot 24/7 and dedicated. They will have a battery back up when the circuit/power is down that will light them up for ruffly an hour. Put them on with ur night lights is what i would do.
 
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