Emergency lighting Panel not connected ahead of main service switch?

[batman2010]

My understanding of an emergency panel is that it has to be connected ahead of main service switch so in case of a loss in power due to a short circuit , the emergency lights will stay on.
I am looking at some design drawings and i see that they connected emergency lights through a circuit breaker in a regular panel and marked it as "locked in an ON position" , my question is what is the point of this? if you have a short circuit on the panel, the main breaker feeding the panel will trip and doesn't matter if my emergency lights circuit breaker is ON or Off anymore , because there will be no power to the panel! also according to NFPA 101 chapter 7:
7.9.2.2* The emergency lighting system shall be arranged to provide the required illumination automatically in the event of any interruption of normal lighting due to any of the following:

(1) Failure of a public utility or other outside electrical power supply.
(2) Opening of a circuit breaker or fuse.
(3) Manual act(s), including accidental opening of a switch controlling normal lighting facilities.

and i think this disqualify the existing design of emergency lighting system!

 

[waross]

Emergency lights are generally able to be supplied from an alternate source and will come on or stay on in the event of a failure of the normal supply. The failure of normal power causes the emergency panel to switch to the alternate supply and turn on the emergency lights if they are not already on.
If you connect ahead of the main breaker, then the emergency panel will not be activated in the event of a main breaker trip.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[mcgyvr]

Yep.. never seen an "emergency" light without a battery in it.

 

[DRWeig]

Agree with the others, the emergency lights will have batteries in them. The "locked ON" warning is to keep anyone from switching it off and allowing the batteries to go totally dead.

Best to you,

Goober Dave

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[FreddyNurk]

There are a number of ways to approach emergency lighting, and obviously standards change depending on location.

Most of the emergency lighting systems these days have integral batteries and a supply feed that not only charges the batteries, but monitors the supply for dropout. The single biggest issue with these is the battery, they don't last that long, they're generally all over the plant and hard to get to, and the batteries need to be both tested and replaced when they fail. Its often cheaper to change the whole unit out than it is to just replace the battery.

This then leads to the provision of either testing buttons on the side of each unit (which tell you if the lamp works, but not if it'll stay lit for the code required time) or an integral testing facility as part of the distribution board (which can be where you get the single feed for the entire emergency lighting system, as its easier to test all of them that way). It does nothing for a single lighting circuit within the building tripping as it won't energise unless the whole lot goes down (which is pretty much the same as what waross has indicated).

Code (standard) dependent, its possible to put in a central battery bank for emergency lighting circuits rather than individual batteries all around the place. This makes maintenance easier, but also means that its then just as susceptible to a short in the cabling as a normal lighting system. Other reasons for deviation from emergency lighting systems with integral backup batteries include the requirement for a run time longer than what the standard allows (say, you want 6 hours of operation for a battery backed light but emergency lighting only runs for 2 hours).

The standards relevant to my location have some of these requirements present (say, testing facility, and the minimum battery operation duration requirement) though I cannot say if the NFPA has these.

 

[EEJaime]

Batman2010,
As the others have stated, there are many ways to implement emergency lighting. Most common for commercial installations is the aforementioned "unitary" equipment where you have one battery for one fixture located throughout your plant. The central inverter type battery system has also been mentioned, and explained that while solving maintenance issues it still introduces a single point of failure that somewhat decreases system reliability. Cost is also a major factor. UPS or Emergency Lighting System Inverters cost. Some dearly. You also need real estate as some of these systems have hefty footprints. Systems are now available, both unitary equipment and central inverter equipment which are intelligent and will notify maintenance when a battery is going down, or a charger shorts, or a line experiences a fault. More costly, but in critical facilities we always include this capability.

More common in facilities such as Hospitals, large schools, government facilities, and such is the Standby Emergency generator that would supply Life Safety loads, (Egress lighting, exit signage, alarm and alerting systems), Critical loads,(for hospitals patient care, lab equipment, etc...), and Equipment loads, (heating, process equipment, elevators, etc...). The salient feature of all these systems is a secondary source of power that is or becomes available in the event of any failure on the normal system power supply. The only thing that we see regularly connected ahead of a facilities' main service disconnect is a Fire Pump. Those are a completely different animal with their own set of rules.

Good luck to you,

EEJaime