I have an existing building with an existing generator that only supports an ATS serving an emergency panel w/ NEC 700 emergency fixtures. The generator is being replaced with a larger one to back up the entirety of the service. Rather than provide a generator with two output breakers would it be acceptable to remove the emergency lighting circuits from the existing emergency panel and run them through an appropriate UPS or inverter? I know that the UPS would always see normal power since the generator is backing up the normal source, is this problematic? Is there such a thing as a UPS that can interlock with a generator in a way that the UPS would remain on until the signal from the generator is removed. I'm just trying to find a workaround that could save us the cost of a generator with an additional load breaker, two disconnects, and one transformer.
Emergency Lighting Backup Source
- Thread starter ADub
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hillbilly1
Senior Member
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- North Georgia mountains
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- Owner/electrical contractor
You would also need a second transferswitch.
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- Lockport, IL
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A central inverter that can supply the egress lights for 90 minutes, and be on-line within 10 seconds of the loss of utility power, would be acceptable. In this case, the generator is not an emergency component. If the owner wants to keep the building operating, then a generator powering the entire building would provide that. But keep in mind that the purpose of the egress lights is to enable the occupants to safely leave the building.
If the new generator cannot be on-line in 10 seconds and keep power to the egress lights for at least 90 minutes, then you can't take credit for it as being the required emergency power source. But if it does have these two capabilities, and if you do all the maintenance and testing that an emergency generator would require, then a UPS is not needed. That might prove to be more expensive than a second generator breaker.
If the new generator cannot be on-line in 10 seconds and keep power to the egress lights for at least 90 minutes, then you can't take credit for it as being the required emergency power source. But if it does have these two capabilities, and if you do all the maintenance and testing that an emergency generator would require, then a UPS is not needed. That might prove to be more expensive than a second generator breaker.
hillbilly1
Senior Member
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- North Georgia mountains
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- Owner/electrical contractor
After re-reading the post. The second breaker would be the cheapest and easiest way to go. Doesn’t matter if the utility side of the existing switch is fed after the service transferswitch, but the new generator would still have to meet the criteria of article 700 as Charlie pointed out.
Strathead
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- Ocala, Florida, USA
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- Electrician/Estimator/Project Manager/Superintendent
I don't see this. Please explain.
hillbilly1
Senior Member
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- North Georgia mountains
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- Owner/electrical contractor
The article 700 loads require a separate transferswitch which is fed from the second generator breaker. You can use the existing switch, and it will be in series with the service rated switch.
Strathead
Senior Member
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- Ocala, Florida, USA
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- Electrician/Estimator/Project Manager/Superintendent
But, in the proposed scenario, the generator feeds the entire electrical system from a single breaker. Transfer switch one. The MSB has a breaker that feeds a UPS (where the article 700 emergency system now starts), which by nature transfers power to the batteries when it senses loss of power. Which feeds the article 700 emergency panel. No second transfer switch.
hillbilly1
Senior Member
- Location
- North Georgia mountains
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- Owner/electrical contractor
I’m just saying it would be much cheaper going with adding the second breaker (which they can easily do from the factory) and using what you have. Leave the existing transferswitch alone. You could even leave the existing generator if it is still in good condition, just more maintenance. If the new generator fails, the old one starts up and takes over, and you stay in compliance. Also the UPS would probably need to rated for article 700 loads.
I would typically agree with this but the problem with the second breaker is it’s not just a second breaker on the generator. The new genset is 480/277 and the existing service is 208/120. So just to feed the 700 loads I’ll need the second gen breaker, a primary fused disconnect, a 75kva tx, a secondary fused disconnect, and a new 700 ATS. I’m trying to find a way to save this customer what would be a pile of money while still keeping the engineer happy.
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This is exactly what I’m looking into. My only concern is that when the main system loses power both the generator and the UPS will change state, the generator will obviously run until normal power is restored but the UPS will sense “normal” power as soon as ATS 1 switches. The UPS can’t know if its normal source is the utility or the generator, but it would still be effective in a complete power loss scenario
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hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
Why do you need a 700 amp transferswitch for the article 700 loads? Unless the ups has internal conversion for 480 to 120/208, then you still will need the transformer.
I meant an ATS for the article 700 loads, not a 700 amp transfer switch. The article 700 lights are 120 volts, the generator is 480/277. Using the generator as the emergency source requires a transformer and disconnects and a lot more pipe and wire. A one-line is worth a thousand words here. Basically I just wanted to know if anyone has used a properly rated UPS for article 700 loads over an emergency genset.
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hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
Yes, it can be done, the generator does not make any difference. The inverter can have an off delay if the main lights are HID, and require a cooldown period before they re-start.
That’s what I was thinking. The building will have an optional standby system covering the entire service no matter what, and the engineer is entrenched in the opinion that the generator also needs to be the emergency source for the article 700 lights. I’m trying to propose a more economical option that would save tens of thousands of dollars.
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Strathead
Senior Member
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- Ocala, Florida, USA
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- Electrician/Estimator/Project Manager/Superintendent
Which would be perfectly legal.