malachi constant
Senior Member
- Location
- Minneapolis
I was curious about generator sizing and ran across this excellent thread: http://forums.mikeholt.com/showthread.php?t=111906
I hadn't realized the NEC had changed to require the generator to be sized to Article 220.
But sizing the generator to Art 220 does not necessarily mean the generator is adequately sized, correct? You could have some monster loads that if not sequenced could theoretically all start at the same time, causing inrush currents that are inappropriate for a genset sized straight to Art 220.
I typically plug the calculated building loads into a generator sizing program, and when I see the unbelievably large set it suggests I start sequencing and using what I assume are reasonable diversity factors to bring it down (i.e. if all lights are on occ sensors then they won't all be on at same time; plug loads won't be 100% of what code calculates, etc).
My point is you can use a generator sizing program and if poor assumptions are used it could oversize the genset by a very large factor. And if you follow 702.5 and only use 220 to size it, you could significantly undersize the genset if you have large loads you aren't sequencing.
Am I correct? Just trying to bounce this off folks more knowledgable than myself. Thanks!
I hadn't realized the NEC had changed to require the generator to be sized to Article 220.
But sizing the generator to Art 220 does not necessarily mean the generator is adequately sized, correct? You could have some monster loads that if not sequenced could theoretically all start at the same time, causing inrush currents that are inappropriate for a genset sized straight to Art 220.
I typically plug the calculated building loads into a generator sizing program, and when I see the unbelievably large set it suggests I start sequencing and using what I assume are reasonable diversity factors to bring it down (i.e. if all lights are on occ sensors then they won't all be on at same time; plug loads won't be 100% of what code calculates, etc).
My point is you can use a generator sizing program and if poor assumptions are used it could oversize the genset by a very large factor. And if you follow 702.5 and only use 220 to size it, you could significantly undersize the genset if you have large loads you aren't sequencing.
Am I correct? Just trying to bounce this off folks more knowledgable than myself. Thanks!