main panel size with 100A subpanels?
- Thread starter julesm
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panel
panel
smart*** answer would be by Art 220
seriously, you would need to look at specific loads plus the requirements of 220.3.
Assuming you are looking at a 480v3phase panel (with 3 phase breakers), the 100 amp breakers to the 75 kva might be a bit on the low end, but if the transformers are loaded, a 100 amp load per transformer would be a "good" number.
As far a the other two panels, you, agan would need to look at the actaul load. If you are trying to cover from the end user's standpoint, I guess figure 100 amps for each load, although the transformers might exceed that a bit.
panel
smart*** answer would be by Art 220
seriously, you would need to look at specific loads plus the requirements of 220.3.
Assuming you are looking at a 480v3phase panel (with 3 phase breakers), the 100 amp breakers to the 75 kva might be a bit on the low end, but if the transformers are loaded, a 100 amp load per transformer would be a "good" number.
As far a the other two panels, you, agan would need to look at the actaul load. If you are trying to cover from the end user's standpoint, I guess figure 100 amps for each load, although the transformers might exceed that a bit.
Last edited:
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- Semi-retired engineer
why do you even need a main with only four breakers?
I was trying to simplify the question and therefore wasn't clear...
Art 220 is a big help, of course.
My confusion I think is that the initial loads are small, so I don't want to terribly undersize my service.
So with, as in my simple example, let's assume each 100A panel and transformer has a connected, let's say continuous, load of 30A.
30 x 1.25 = 37.5A
37.5A x 4 = 150A.
So I could use a 150A service to comply with 220. But that leaves no room for future growth. So maybe I'll do a 300A panel.
My question ultimately is, when future growth is unknown, how do you decide?
Thanks,
JM
Art 220 is a big help, of course.
My confusion I think is that the initial loads are small, so I don't want to terribly undersize my service.
So with, as in my simple example, let's assume each 100A panel and transformer has a connected, let's say continuous, load of 30A.
30 x 1.25 = 37.5A
37.5A x 4 = 150A.
So I could use a 150A service to comply with 220. But that leaves no room for future growth. So maybe I'll do a 300A panel.
My question ultimately is, when future growth is unknown, how do you decide?
Thanks,
JM
GilbeSpark
Senior Member
- Location
- NC
Is this a product you're providing for a customer? If so, ask them what they want.
Is this something for a company you work for? If so then plan for the future. A few extra dollars now can save the company more down the road, plus the hassle of having to upgrade later on.
Is this something for a company you work for? If so then plan for the future. A few extra dollars now can save the company more down the road, plus the hassle of having to upgrade later on.
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