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#83064 - 01/07/03 02:31 PM Aluminum Busbar Calculations  
gregoryf  Offline
Member
Joined: Aug 2002
Posts: 19
Ketchikan AK USA
I am hoping someone can help me determine the maximum allowable current carrying capacity for Aluminum Busbar. I need to install some busbar.
I have 1/4" X 4" and 3/8" X 4" to choose from.
What is the ampacity of each? Would you please tell me how to figure this out and cite reference, if possible?
Thank you all so much!
I really like this board!


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#83065 - 01/07/03 03:12 PM Re: Aluminum Busbar Calculations  
Redsy  Offline
Member
Joined: Mar 2001
Posts: 2,056
Bucks County PA
Did a search and came up with this, but it is for copper.
Try an internet search. http://www.stormcopper.com/design/Ampacity-Quick-Chart.htm


#83066 - 01/07/03 04:49 PM Re: Aluminum Busbar Calculations  
cubby964  Offline
Member
Joined: Oct 2002
Posts: 67
USA
Try NEC 366.7 (A)


#83067 - 01/07/03 07:01 PM Re: Aluminum Busbar Calculations  
Bjarney  Offline
Moderator
Joined: Apr 2002
Posts: 2,527
West-Southern Inner-Northeast ...
Gregory, a conservative rule of thumb for Aluminum is 700 amperes/in². Based on that, ~700/1150A. {Suggest Belleville washers while you're at it.}

Copper—1000 amperes/in²

See 99NEC 374-6(a).




[This message has been edited by Bjarney (edited 01-07-2003).]


#83068 - 01/07/03 07:04 PM Re: Aluminum Busbar Calculations  
JBD  Offline
Member
Joined: Jul 2001
Posts: 599
WI, USA
There are several factors to consider.

What temperature rise above what ambient?
What is the conductivity of the conductor (an old book shows two types of aluminum EC - 61%IACS and EC-T61 - 57%IACS)?
What is the orientation of the bars, flatwise or on edge?
Are bars mounted above each other (stacked)?

For example:
30 deg C rise over 40C ambient, still but unconfined air
EC-T61 aluminum
Edgewise orientation, bars spaced at least one thickness apart.
AC 60hz current

3/8 x 4 = 1170A
1/4 x 4 = 960A


#83069 - 01/07/03 07:49 PM Re: Aluminum Busbar Calculations  
gregoryf  Offline
Member
Joined: Aug 2002
Posts: 19
Ketchikan AK USA
Thank you all for your replies.

JBD,
I was wondering where you found the info to calculate the ampacity? Why does it matter which way they are stacked?

Thank you!


#83070 - 01/07/03 11:42 PM Re: Aluminum Busbar Calculations  
sparky66wv  Offline
Member
Joined: Nov 2000
Posts: 2,236
West Virginia
Heat rises?

Just a guess...

[Linked Image]


-Virgil
Residential/Commercial Inspector
5 Star Inspections
Member IAEI

#83071 - 01/08/03 10:57 AM Re: Aluminum Busbar Calculations  
JBD  Offline
Member
Joined: Jul 2001
Posts: 599
WI, USA
Yes, orientation affects heat transfer.

I got my basuic info from an old (1964) reference from Anderson Electric.

For current aluminum bussing information try: http://www.alcoa.com/afl_tele/en/pdf/catalog/catalogs/BusCondCatalog.pdf


#83072 - 01/08/03 06:18 PM Re: Aluminum Busbar Calculations  
WARREN1  Offline
Member
Joined: May 2001
Posts: 176
Greenville, SC, USA
It sure is nice to have an old Anderson Reference book. Mine is a '64 version also, and I use it many times to get information not readily available. I wish they would reprint it, or publish it on the web.



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