DC Powered Exit Sign

[ron]

Does anyone know of a DC powered exit sign. Maybe 24V? A client of mine has a really reliable 24V DC plant (Telephone Company) and wants to feed the exit signs from their plant rather than have separate backup batteries located at each sign.
Would you think that this non-power limited DC branch circuit would require conductors in raceway or cable only per 725?

 

[hurk27]

I don't know what code says about this, but I have always understood that the isolated back up power the batteries supply at each unit, provide a more dependable power source, as they will still light even if one or more exit signs were involved in the fire, if a common power source was to be used, all the exit signs would stop working if any of the exit sign or supply conductors was involved in the fire.

similar as to the reason a central fire alarm cant over ride the requirements of having battery back up smoke detectors.

but again I'm not sure about this.

I should add that years ago we used to install a DC power system to power all the exit and emergency light, but I haven't done one of those in many years

 

[hurk27]

Look at it this way, the whole reason for battery back up is because of the common electric supply that can be taken out in a fire, so what good would it do if you also made the battery back up a common supply that can also be taken out, by a fire?

Even if it is not required by code I would lean toward the isolated battery back up

 

[ron]

Wayne,
I would guess that the central nature of the supply is not an issue. I could put in a central emergency lighting inverter or a Article 700/701 gen to take care of emergency lighting issues, and it would be okay.

 

[don_resqcapt19]

Ron,
I don't really see how Article 725 would apply.

725.1 Scope.
This article covers remote-control, signaling, and power-limited circuits that are not an integral part of a device or appliance.

I don't see the circuit as any of the things that are within the scope of Article 725. A Chapter 3 wiring method will be required.

 

[don_resqcapt19]

Look at it this way, the whole reason for battery back up is because of the common electric supply that can be taken out in a fire, so what good would it do if you also made the battery back up a common supply that can also be taken out, by a fire?

Even if it is not required by code I would lean toward the isolated battery back up

I think the real reason for the local battery back-ups is because they are a cheap way to meet the emergency lighting rules.

 

[ron]

Don, I see you point regarding the scope of 725.

Now to try an find a sign that is DC powered. I don't think an AHJ will allow me to take a battery powered sign, throw away the batteries and hot wire the terminals, as it isn't listed that way.

 

[satcom]

Look at it this way, the whole reason for battery back up is because of the common electric supply that can be taken out in a fire, so what good would it do if you also made the battery back up a common supply that can also be taken out, by a fire?

Even if it is not required by code I would lean toward the isolated battery back up

Phone plants do have fires
http://www.google.com/search?hl=en&q=ny+telephone+exchanse+fire&aq=f&oq=&aqi=

I remember a situation where the phone company refused to have a monitored fire alarm system, because that thought one of there operators would respond to a local signal at the plant, the operator never responded and the plant burnt to the ground, leaving a wide area without phone service, so cheap out on safety and your reward may be a big loss.

Enjoy reading thru the links of electrical fires in phone plants.

 

[hurk27]

I think the real reason for the local battery back-ups is because they are a cheap way to meet the emergency lighting rules.

This was my thinking of the only way to meet this requirement in 700.12

Equipment shall be designed and located to minimize the hazards that might cause complete failure due to flooding, fires, icing, and vandalism.

any system with a common back up feed would be subject to failure if any part of the system that was to get involved with the fire. It would be almost imposable to design a common source supplied system, that could not be taken out by the fire. but with the backup supply at each unit or a area of units, each would work independently of each other and would keep functioning. and for the fact they would be powered by the local lighting circuit even a breaker failure of the lighting circuit would still provide for the EMG lights to come on.

Again this is only my opinion, of what makes sense to me.

 

[hurk27]

Don, I see you point regarding the scope of 725.

Now to try an find a sign that is DC powered. I don't think an AHJ will allow me to take a battery powered sign, throw away the batteries and hot wire the terminals, as it isn't listed that way.

I think a problem will be the testing of each unit, done in most cases by a fire inspector of commercial buildings, here they come around every 6 months or so.

also most exit sign will have 6 or 12 volt lamps, so finding a 24 volt model will be tough.

Another problem is with the advent of going to LED system which last much longer then the incandescent lamps, they will be replacing the lamps more often. for the cost of LED exit signs today, I cant see the benefit of going through all of this trouble to avoid local batteries. we get LED exit signs for $17.00-$19.00 and sometimes even lower. never had a problem with them.

 

[don_resqcapt19]

This was my thinking of the only way to meet this requirement in 700.12


any system with a common back up feed would be subject to failure if any part of the system that was to get involved with the fire. It would be almost imposable to design a common source supplied system, that could not be taken out by the fire. but with the backup supply at each unit or a area of units, each would work independently of each other and would keep functioning. and for the fact they would be powered by the local lighting circuit even a breaker failure of the lighting circuit would still provide for the EMG lights to come on.

Again this is only my opinion, of what makes sense to me.

Wayne,
I see your point, but there are central emergency lighting systems on the market.

 

[GUNNING]

First if the place burns up nobody is going to call anyone.
Second, there are dc extension lights you can purchase and 101 says you dont need a self illuminated exit light but an exit sign that is illuminated, point one of the little lights on the sign.
Anyone know if NEC covers DC? Im thinking the phone company might have its own set of codes for this. They are experts at DC.