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Aluminum Busbar Calculations #83064
01/07/03 01:31 PM
01/07/03 01:31 PM
gregoryf  Offline OP
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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Re: Aluminum Busbar Calculations #83065
01/07/03 02:12 PM
01/07/03 02:12 PM
Redsy  Offline
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.

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

Re: Aluminum Busbar Calculations #83067
01/07/03 06:01 PM
01/07/03 06:01 PM
Bjarney  Offline
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).]

Re: Aluminum Busbar Calculations #83068
01/07/03 06:04 PM
01/07/03 06:04 PM
JBD  Offline
Joined: Jul 2001
Posts: 599
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

Re: Aluminum Busbar Calculations #83069
01/07/03 06:49 PM
01/07/03 06:49 PM
gregoryf  Offline OP
Joined: Aug 2002
Posts: 19
Ketchikan AK USA
Thank you all for your replies.

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

Thank you!

Re: Aluminum Busbar Calculations #83070
01/07/03 10:42 PM
01/07/03 10:42 PM
sparky66wv  Offline
Joined: Nov 2000
Posts: 2,236
West Virginia
Heat rises?

Just a guess...

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Re: Aluminum Busbar Calculations #83071
01/08/03 09:57 AM
01/08/03 09:57 AM
JBD  Offline
Joined: Jul 2001
Posts: 599
Yes, orientation affects heat transfer.

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

For current aluminum bussing information try:

Re: Aluminum Busbar Calculations #83072
01/08/03 05:18 PM
01/08/03 05:18 PM
WARREN1  Offline
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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