ECN Forum Forums Code Related Discussion NEC & other Code issues Aluminum Busbar Calculations

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!

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

Try NEC 366.7 (A)

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).]

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

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!

Heat rises?

Just a guess...

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

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.