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A Good Electrician
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Hey Guys. Firstly, I understand that there are a LOT of heat, voltage, Megger, distance, etc tests that go into properly building distribution boards, gear and such. However, I'm desperate for some sort of "quick reference" or resource that can help me find the Allowable ampacity of Bus Bar.
I have a situation were a Sub was hired to retrofit (2) pieces of gear for an 800 Amp Distribution board into (1) piece because of code issues with distance and clear working space. And now I'm doing the install, testing, and energizing of said gear. Now, I've meet with the guys who built it and they are a good outfit and in general "good" guys. However, I've never been one to be comfortable with the "just put it in" approach.
Does anyone know of a good resource that explains a bit about properly sizing busbar? Thank you in advance for any and all help, advice or direction.

Ben
"If you want to go fast, go alone. If you want to go far, go together."
 

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Hey Guys. Firstly, I understand that there are a LOT of heat, voltage, Megger, distance, etc tests that go into properly building distribution boards, gear and such. However, I'm desperate for some sort of "quick reference" or resource that can help me find the Allowable ampacity of Bus Bar.
I have a situation were a Sub was hired to retrofit (2) pieces of gear for an 800 Amp Distribution board into (1) piece because of code issues with distance and clear working space. And now I'm doing the install, testing, and energizing of said gear. Now, I've meet with the guys who built it and they are a good outfit and in general "good" guys. However, I've never been one to be comfortable with the "just put it in" approach.
Does anyone know of a good resource that explains a bit about properly sizing busbar? Thank you in advance for any and all help, advice or direction.

Ben
"If you want to go fast, go alone. If you want to go far, go together."
This is not at all simplistic, there is a lot that goes into it. But I use these charts as a cross check.

http://www.stormcopper.com/design/Ampacity-Quick-Chart.htm

But to give you an idea of how different it can be, we use 1/8 x 3" bus for 600A. According to this chart, even at only a 30C rise, they show 1/8 x 3 bus as being 700A. So I know from this comparison that my guys are being conservative, and I like that.
 

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If the busbar was installed in an auxiliary gutter, then the following NEC rule would apply.
366.23 Ampacity of Conductors
(A) Sheet Metallic Auxiliary Gutters. Where the number of current-carrying conductors contained in the sheet metallic auxiliary gutter is 30 or less, the adjustment factors specified in 310.15(B)(3)(a) shall not apply. The current carried continuously in bare copper bars in sheet metallic auxiliary gutters shall not exceed 1.55 amperes/mm2 (1000 amperes/in.2) of cross section of the conductor. For aluminum bars, the current carried continuously shall not exceed 1.09 amperes/mm2 (700 amperes/in.2) of cross section of the conductor.
 

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Ampacity is the easy part, but if you changed the fault current you have bus bracing to worry about, that is more complicated.
 
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