Emergency & Stand-by Gen Question

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GamecockEE

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Looking at a situation where it is desirable to utilize a single generator for both Article 700 & 701 loads. Been reading previous posts on this issue and they have been very informative as well.
My copy of NFPA 110, and reading of article 700,701,& 702 seems to indicate that the generator could utilize a single main breaker(part of the Gen unit) that would feed two stand-alone feeder breakers (one for article 700 loads, the other for article 701 & possibly 702 type loads). Of course, these feeder breakers would supply individual ATS. Is there anything wrong with this typology, or does the generator absolutely have to have two mains, one for Emergency, the other for Legally required 7 optional Stand by. Thanks for the education!
 
Re: Emergency & Stand-by Gen Question

I'm working in a building at this time that has a single 1.5 MW genset providing both types of loads. It feeds it's own MDP board with a main and five breakers. Each one of these breakers then feeds a separate xfer switch.
 
Re: Emergency & Stand-by Gen Question

Good analogy, Paul. I see both situations as being essentially equivalent, and both situations as being equally acceptable.
 
Re: Emergency & Stand-by Gen Question

Paul, Is this MDP board supplying just Emergency (article 700 type loads) or do they contain legally required and/or optional stand-by as well?
How are you going about meeting the requirements of 700.5(B), which calls for "automatic selective load pick-up & load shedding". Or are you using the 2005 version which allows for pick up of all loads where there is sufficient generator capacity? Sorry for all the questions,just trying to learn.
 
Re: Emergency & Stand-by Gen Question

700.5(B):
"where selective load pickup and load shedding is provided as needed to ensure....."

It looks to me like load shedding is only required is the total connected load is larger than the generator. If the generator is capable of supplying all connected loads, why would load shedding be needed?

Anyhow, you can specify an automatic transfer switch with load shedding. I think it senses the generator voltage or frequency, and drops out if one or the other drops.

I have never had to use 2 levels of load shedding (ie. drop the optional loads, then drop the legally required loads). But there might be adjustable setpoints for how much the voltage or frequency drops before a transfer switch drops the load.

Steve
 
Re: Emergency & Stand-by Gen Question

Originally posted by GamecockEE:
Paul, Is this MDP board supplying just Emergency (article 700 type loads) or do they contain legally required and/or optional stand-by as well?
How are you going about meeting the requirements of 700.5(B), which calls for "automatic selective load pick-up & load shedding". Or are you using the 2005 version which allows for pick up of all loads where there is sufficient generator capacity? Sorry for all the questions,just trying to learn.
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HVAC controls sense when the load is being ran off of generator power or utility power and adjust accordingly. Although, I do believe that this particular genset is sized larger than the calculated load so no load shedding occurs.

This setup was installed back in 93-94, which I was a part of. It had a 100kw genset at that time, which picked up the required 700 load and a UPS system for their IT room. That genset fed two xfer switches for the two different loads. We added the MDP back then, which picks up both 700 and 701 loads, plus three more xfer switches. Then we picked up numerous existing panels so they'd be on the generator system. We also added a second, and much larger, 500 kva UPS system.
 
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