Full Back-Up Generator and Emergency Loads

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msilva94

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Location
PA, USA
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Electrical Engineer
Hello all,

I’m working on a site where the client wants the entire 800A Main Distribution Panelboard (MDP) backed up by a single generator.
They also want to avoid using battery backups for emergency lighting. I'm figuring to place the lighting on a new 100A Panel 'EM', but not sure how to provide normal power to it.

Per code, emergency lighting must be powered from a source separate from normal lighting.
Here was my brief thought:
  • 800A MDP powers:
    • Circuit 1 – 400A Panel 'A'
    • Circuit 2 – 400A Panel 'B'
    • Circuit 3 – 100A Panel 'EM'
  • 800A ATS feeds the MDP (normal loads backed up by generator)
  • 100A ATS feeds Panel 'EM' (emergency lighting backed up by generator)
The issue is that if Panel 'EM' is fed from the MDP, this creates a loop.
I’m struggling to figure out a simple solution without introducing more equipment.

Thanks in advance.
 
I don't know how to do emergency lighting without a battery pack. Either at the light(s) or some type of inverter system.

If this is normal lights that they want backed up by the generator then you are okay. That isn't considered emergency lighting. The lighting required for egress during an outage, fire or similar event are considered emergency lights. Like the exit signs.
 
Elect117 said:
I don't know how to do emergency lighting without a battery pack. Either at the light(s) or some type of inverter system.

If this is normal lights that they want backed up by the generator then you are okay. That isn't considered emergency lighting. The lighting required for egress during an outage, fire or similar event are considered emergency lights. Like the exit signs.
Click to expand...
If the fixtures are battery inverter driven, it’s not too big of a deal. It appears the transferswitch for the emergency lights is separate from the other loads which is required, but the generator will have to start, and that transferswitch transfers in under 10 seconds to qualify. If not, then the battery backup must be maintained. If the emergency lighting is battery powered heads, such as bug eyes, new wiring will be required to existing fixtures to provide illumination requirements.
 
Keep inn mind that if you use the generator as an emergency supply to e lights, that wiring must be seperate from other wiring. Suggest a review of Art 700. It’s much simpler to use battery e lights.
 
qcroanoke said:
Is this a legally required emergency system?
And as Tom said battery emergency lights would make life much easier...
Click to expand...
This is a really good point, many people call normal back-up generators, "emergency back-up" when they are not legally required.
 
don_resqcapt19 said:
You run circuits from an Article 700 Emergency System. Have done it a few times per project specs.
Click to expand...

I guess I am a little confused. Lets say we have a lighting panel feeding all of the lights with egress / EM lights on certain branch circuit(s). I thought those lights would require a battery system at the light or a panel that is feed by an inverter + battery from a feeder. Then the lights come off that.

I didn't think there was a way to feed it off gas generator because the loss of power for however many seconds was a problem. But I guess not. 700.12 give you up to 10 seconds. I just thought battery in the light or on an inverter battery system was the normal.
 
msilva94 said:
The issue is that if Panel 'EM' is fed from the MDP, this creates a loop.
I’m struggling to figure out a simple solution without introducing more equipment.
Click to expand...
If you really want to have emergency lighting, you will have to apply Article 700. The normal power for the 100 amp EM panel would have to come from the line side of the 800 amp MDP.
 
You can feed the normal source of the 100A EM-ATS from the MDP. That ATS can be configured to inhibit re-transfer to normal source until utility power is restored. That way you don't see additional interruptions if using open-transition switches.
 
mauk said:
You can feed the normal source of the 100A EM-ATS from the MDP. That ATS can be configured to inhibit re-transfer to normal source until utility power is restored. That way you don't see additional interruptions if using open-transition switches.
Click to expand...
Thank you for this response. This would be solely controlled and configured within the ATS itself? I'm curious, and maybe this is a question geared to a generator vendor, but how can the ATS be configured to inhibit re-transfer to MDP while the generator is supplying both the Feed Panel (MDP) and the Emergency Panel? Does this require any additional equipment or just an ATS called out appropriately?
 
msilva94 said:
Thank you for this response. This would be solely controlled and configured within the ATS itself? I'm curious, and maybe this is a question geared to a generator vendor, but how can the ATS be configured to inhibit re-transfer to MDP while the generator is supplying both the Feed Panel (MDP) and the Emergency Panel? Does this require any additional equipment or just an ATS called out appropriately?
Click to expand...
You need to review life safety codes and generator codes as well if you are setting up an emergency system. For example the emergency transfer switch needs to be in a different room or space. The article 700 "Legally Required" has caused me confusion in the past. It can actually be applied two different ways in this context. The codes require the emergency lighting etc. to be on a secondary power source. But really I look at it like, in a normal building emergency lights are required and they need to be on in a power outage. In most cases, nothing says I can't power them individually from batteries, but IF I WANT to power them from a generator then the system that powers them is the legally required secondary power and then it falls under article 700 plus the other building codes I cited. You don't mention it, but the generator needs both an 800 A and a 100A breaker I would also say it may need load shedding on all of some of the 800A load.
 
msilva94 said:
Hello all,

I’m working on a site where the client wants the entire 800A Main Distribution Panelboard (MDP) backed up by a single generator.
They also want to avoid using battery backups for emergency lighting. I'm figuring to place the lighting on a new 100A Panel 'EM', but not sure how to provide normal power to it.

Per code, emergency lighting must be powered from a source separate from normal lighting.
Here was my brief thought:
  • 800A MDPpowers:
    • Circuit 1 – 400A Panel 'A'
    • Circuit 2 – 400A Panel 'B'
    • Circuit 3 – 100A Panel 'EM'
  • 800A ATS feeds the MDP (normal loads backed up by generator)
  • 100A ATS feeds Panel 'EM' (emergency lighting backed up by generator)
The issue is that if Panel 'EM' is fed from the MDP, this creates a loop.
I’m struggling to figure out a simple solution without introducing more equipment.

Thanks in advance.
Click to expand...
Remove
Circuit 3 – 100A Panel 'EM' in 800A MDP
Connect normal power 100ATS througjh separate independent circuit tapping line terminals 800A ATS
 
Strathead said:
You need to review life safety codes and generator codes as well if you are setting up an emergency system. For example the emergency transfer switch needs to be in a different room or space. The article 700 "Legally Required" has caused me confusion in the past. It can actually be applied two different ways in this context. The codes require the emergency lighting etc. to be on a secondary power source. But really I look at it like, in a normal building emergency lights are required and they need to be on in a power outage. In most cases, nothing says I can't power them individually from batteries, but IF I WANT to power them from a generator then the system that powers them is the legally required secondary power and then it falls under article 700 plus the other building codes I cited. You don't mention it, but the generator needs both an 800 A and a 100A breaker I would also say it may need load shedding on all of some of the 800A load.
Click to expand...
Normally, I would have a set up like this

1600A MDP (Utility power)
800A Critical Panel (Equipment, etc) -> Normal Power from 1600A MDP
300A Life Safety Panel -> Normal Power from 1600A MDP

750kVA Generator
100% Rated 300A Circuit Breaker 1 -> 300A ATS -> 300A Life Safety Panel
This CB is to be first to be energized per life safety (10 second start up).
80% Rated 800A Circuit Breaker 2 -> 800A ATS -> 800A Critical Panel
This CB is to be energized next (30 second start up).

In this example, Life Safety and Critical are both Normal Powered off of the MDP, and Backed up by the GenSet.


However, in my case, the entire MDP is going to be backed up by the GenSet.

As I understand the code, life safety does not need to be in a different location from normal, as long as the room is 2-hr rated at a minimum. However, back-up power and normal power cannot come from the same source. This is the part I'm confused on, because it almost loops.

Right now it's

800A MDP (Utility Powered w/ Service Entrance Rated ATS for GenSet connection)
100A Life Safety Panel (Normal Power from 800A MDP, ATS for GenSet Connection).
Within 10 seconds the life safety panel turns on.
Within 30 seconds after, the MDP is then completely energized.

Is this still the same source even though it's running off GenSet? Is there an issue with the Life Safety ATS once the MDP is energized? The previous comment said that the Life Safety ATS can be configured to not re-initiate normal off of the MDP, but then I'm not sure how it'll re-initiate when normal power does return.
 
msilva94 said:
Thank you for this response. This would be solely controlled and configured within the ATS itself? I'm curious, and maybe this is a question geared to a generator vendor, but how can the ATS be configured to inhibit re-transfer to MDP while the generator is supplying both the Feed Panel (MDP) and the Emergency Panel? Does this require any additional equipment or just an ATS called out appropriately?
Click to expand...
This may vary somewhat by manufacturer, but on a recent project the 'inhibit re-transfer' inputs on the EM-ATS controller were connected to 'emergency position' aux contacts on the Main-ATS.
 
Strathead said:
You need to review life safety codes and generator codes as well if you are setting up an emergency system. For example the emergency transfer switch needs to be in a different room or space. The article 700 "Legally Required" has caused me confusion in the past. It can actually be applied two different ways in this context. The codes require the emergency lighting etc. to be on a secondary power source. But really I look at it like, in a normal building emergency lights are required and they need to be on in a power outage. In most cases, nothing says I can't power them individually from batteries, but IF I WANT to power them from a generator then the system that powers them is the legally required secondary power and then it falls under article 700 plus the other building codes I cited. You don't mention it, but the generator needs both an 800 A and a 100A breaker I would also say it may need load shedding on all of some of the 800A load.
Click to expand...
I noticed they do that in New York, but most other places the transferswitch is next to the other transferswitches in the main electrical room.
 
Deltaforce said:
Remove
Circuit 3 – 100A Panel 'EM' in 800A MDP
Connect normal power 100ATS througjh separate independent circuit tapping line terminals 800A ATS
Click to expand...
Oh, interesting. I didn't even think about tapping off the 800A ATS. I've never done that before.
Would it literally come off the same terminal in the ATS? I'll have to research this a bit.

Edit: should this require a tap can next to the ATS (to follow the NEC 240.21 Tap rules)?
I'm thinking (in the most robust drafting text can provide, pretend the extended periods aren't there...)
800ATS Normal---------
...............................................|
...................................---------------------
................................|............................................|
...............800A MDP(Normal)........... 100A Life(Normal)
 
Last edited:
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