Splitting emergency light power from generator art. 702 power

[Dark Sparky]

I have a facility requiring full-building power backup. It will take a 1200 amp service. Although I will have a full-capacity generator, I would like to avoid needing separate transfer switches (ATS's) for article 700 emergency power vs. article 702 loads. Thus the plan is to have the emergency lights have batteries, and the generator power the rest of the facility's loads (all article 702 loads) in an emergency.

In practice, what is the best way to efficiently "split off" the small amount of normal power for the battery-fed emergency lights? I would like to avoid this obvious approach due to cost: utility power feeds 1200 amp main distribution panel - which splits the power (~1200A to ATS normal power vs. ~100A to the emerg lighting panel) - because downstream of the ATS I would require yet another 1200A MDP - thus a total of (2) 1200A MDP's.

Am I missing an obvious and cost effective solution? (This was a difficult question to nail down a search for in the forums - I can't come up with a search string that narrows down on this question.) Thanks.

 

[d0nut]

Use a service rated, 1200A ATS ahead of your MDP. Then use inverters, integral batteries, emergency lighting units, or some other solution for your emergency egress lighting. You wouldn't need a separate panel for those loads unless you needed to meter them separately or something similar.

 

[Dark Sparky]

Use a service rated, 1200A ATS ahead of your MDP.

I think you mean: feed both the Gen and the Utility power directly to the ATS, then from the ATS feed a 1200A switchboard for the entire facility. I'd love to do that. But it would mean all loads including the (battery powered) emergency lights would be on the generator. I would then have article 700 loads (lights) on the gen, which by my understanding would mandate splitting them off to a second ATS, which I'm trying to avoid.

 

[Strathead]

I think you mean: feed both the Gen and the Utility power directly to the ATS, then from the ATS feed a 1200A switchboard for the entire facility. I'd love to do that. But it would mean all loads including the (battery powered) emergency lights would be on the generator. I would then have article 700 loads (lights) on the gen, which by my understanding would mandate splitting them off to a second ATS, which I'm trying to avoid.

No, you wouldn't. Technically you would have article 700 wiring only from the batteries to the lights. You didn't say what kind of a building you are in. If the AHJ or the building code requires what we really consider "Legally Required Emergency Lighting" meaning fed from an alternative lighting source, then your only option is to run separate transfer switches. Does that make sense? I get hung up on the language sometimes. Virtually all emergency lighting is "legally required". That is why I let my brain just think that every emergency light is technically its own little emergency system.

 

[Dark Sparky]

That's useful to know. This is a police station/courthouse. What does that do for the emergency lighting's classification? Will that mandate two separate transfer switches, or is there an alternate approach?

 

[Dark Sparky]

If two ATS's are needed, I'm particularly interested in an "efficient" incoming distribution for normal power. The generator can have 2 breakers - one to feed each ATS. But for normal power: I'd like to avoid having to have the utility power feed a normal switchboard, then use it to feed each ATS, and then still have another 1200A switchboard after the main/larger ATS.

 

[Strathead]

That's useful to know. This is a police station/courthouse. What does that do for the emergency lighting's classification? Will that mandate two separate transfer switches, or is there an alternate approach?

My guess would be that they will require a secondary powered legally required emergency system and as such require the second transfer switch. Remember it is more than that though. There are physical separation requirements between the transfer switches as well.

 

[hillbilly1]

If the building has a smaller generator, then you are stuck with the two transferswitch scenario, unless you keep the smaller system intact, in which the larger generator, which is an optional standby system, feeds the utility side of the old system. I have retrofitted many Blue box stores that used battery backups for emergency lighting. That system is left in place, and maintained to be compliant.

 

[don_resqcapt19]

That's useful to know. This is a police station/courthouse. What does that do for the emergency lighting's classification? Will that mandate two separate transfer switches, or is there an alternate approach?

Need to make sure they did not specify this building must comply with Article 708 as that would make huge changes.