Corridor Emergency Egress Lighting via GTD20

[Electric-Light]

I would have two issues with your use of the GTD device to connect all lights in a corridor.

1. That doesn't provide the 2 required separate lighting systems - a normal system, and an emergency system. At least that's what I remember the code requiring. By putting all the lights on the emergency you have eliminated any "normal" system.
2. Only necessary, required egress lights can go on the emergency system. You can't just put all the lights on the emergency system. That gives a higher chance a ballast will short, or something will go wrong that will trip a branch breaker and shut off all the emergency lighting in one area.

Now, if you pick every 3rd light and put it on the GTD, I would be good with that.

Yeah that makes sense. If all the lights in the area were on the same branch, a short in one of the fixtures would black out the area. If it is in the emergency string, they obviously can't work.

 

[birtclp]

Are you saying that a short circuit qualifies as a "failure of any individual lighting element" per 700.16?

 

[steve66]

Are you saying that a short circuit qualifies as a "failure of any individual lighting element" per 700.16?

No, not 700.16. But read both 700.15 and 700.17.

 

[birtclp]

No issues with 700.15 IMO. IBC specifies minimum requirements for emergency egress lighting, but there are no limits on maximum levels. Lighting the path of egress to 25 FC instead of 1 FC is permitted.

I read 700.17(2) as permitting the design. Of course how I read it does not matter so much as how the AHJ reads it, so if he is agreeing with you then maybe I am wrong.

I guess my next question would be, if this design is not permitted then why is 2017 NEC adding 700.25 permitting BCELTSs?

 

[north star]

# ~ #


birtclp,

What is the benefit to wiring \ activating all of the egress
lighting versus say 50% of the fixtures ?.......Would the 50%
provide sufficient lighting to egress the space ?


# ~ #

 

[steve66]

No issues with 700.15 IMO. IBC specifies minimum requirements for emergency egress lighting, but there are no limits on maximum levels. Lighting the path of egress to 25 FC instead of 1 FC is permitted.

I read 700.17(2) as permitting the design. Of course how I read it does not matter so much as how the AHJ reads it, so if he is agreeing with you then maybe I am wrong.

I guess my next question would be, if this design is not permitted then why is 2017 NEC adding 700.25 permitting BCELTSs?

I disagree on 700.15. The code is basically saying someone needs to design the egress lighting to have enough to meet the 1FC, but simply placing every light on the emergency circuit is not an option. Especially in an area like a corridor. (I don't think anyone worries about this stuff for a small room or alcove that only has one light.)

700.17 is a tough read for sure. But I took a little more time to read it again, and I read the handbook commentary. I think the basic requirement is that there must be two separate branch circuits present. The handbook talks about "failure of a single branch circuit" and explains that should not leave an area in darkness. I believe your GTD device is supplied from 2 separate branch circuits, and therefore it does meet the requirement of 700.17(1).

700.17(2) would be the more standard installation, where there is normal lighting from a normal branch circuit, and emergency lighting from an emergency branch circuit.

In summary, I still don't think putting all the lights on the GTD complies due to 700.15. Just enough lights on the GTD to get your 1 FC average, and then I think it would be good.

 

[birtclp]

I disagree on 700.15. The code is basically saying someone needs to design the egress lighting to have enough to meet the 1FC, but simply placing every light on the emergency circuit is not an option. Especially in an area like a corridor. (I don't think anyone worries about this stuff for a small room or alcove that only has one light.)

700.17 is a tough read for sure. But I took a little more time to read it again, and I read the handbook commentary. I think the basic requirement is that there must be two separate branch circuits present. The handbook talks about "failure of a single branch circuit" and explains that should not leave an area in darkness. I believe your GTD device is supplied from 2 separate branch circuits, and therefore it does meet the requirement of 700.17(1).

700.17(2) would be the more standard installation, where there is normal lighting from a normal branch circuit, and emergency lighting from an emergency branch circuit.

In summary, I still don't think putting all the lights on the GTD complies due to 700.15. Just enough lights on the GTD to get your 1 FC average, and then I think it would be good.

In my design the corridor lighting is specified as required for emergency use (egress lighting in corridor). The applicable code places a limit on the minimum light level and the uniformity, not the maximum level. To my knowledge applicable code does not limit the number or percentage of fixtures used to provide the required emergency egress lighting. From my perspective whether to place 10%, 50%, or 100% of the light fixtures on the emergency circuit is a design decision.

As for the reason - in this case the Owner requested this, plus there is some savings in only having to run a single conduit down the corridor (from the GTD20 to the light fixtures is an emergency branch circuit).

 

[dkidd]

There is a good article at http://iaeimagazine.org/magazine/2017/02/28/new-rules-and-new-tools-for-emergency-lighting-control/

 

[sterry]

I think that about sums it up. I know from experience that the whole issue of the proper use of load load control relays as permitted in the 2014 NEC is wildly misunderstood in the field by many.
Help me understand something though... while the need for a load control relay in this day and age is obvious, what is the real advantage to using a BCELTS as allowed in 700.25 in the 2017 NEC? You have to wire back to the emergency panel anyway, so why not just power the lights from there in the first place? What am I missing here?

One useful scenario for BCELTS is when the emergency circuit is part of a large dimmer or relay panel utilized for control when normal power is present. If the number of emergency circuits in such a panel is small, it can be more efficient to transfer them out of the panel upon failure of normal power. The alternative would be to use a dimmer or relay panel listed for emergency per 700.23. However, many engineers are uncomfortable feeding such a panel with a reduced size emergency feed and relying on load shedding when normal power fails. Getting the emergency circuits out of the panel upon failure of normal power solves that problem.