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#83064 - 01/07/03 10:31 AM Aluminum Busbar Calculations
gregoryf Offline
Member

Registered: 08/23/02
Posts: 19
Loc: 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 11:12 AM Re: Aluminum Busbar Calculations
Redsy Offline
Member

Registered: 03/28/01
Posts: 2138
Loc: 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

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#83066 - 01/07/03 12:49 PM Re: Aluminum Busbar Calculations
cubby964 Offline
Member

Registered: 10/18/02
Posts: 69
Loc: USA
Try NEC 366.7 (A)

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#83067 - 01/07/03 03:01 PM Re: Aluminum Busbar Calculations
Bjarney Offline
Moderator

Registered: 04/10/02
Posts: 2561
Loc: 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).]

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#83068 - 01/07/03 03:04 PM Re: Aluminum Busbar Calculations
JBD Offline
Member

Registered: 07/12/01
Posts: 599
Loc: 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

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#83069 - 01/07/03 03:49 PM Re: Aluminum Busbar Calculations
gregoryf Offline
Member

Registered: 08/23/02
Posts: 19
Loc: 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!

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#83070 - 01/07/03 07:42 PM Re: Aluminum Busbar Calculations
sparky66wv Offline
Member

Registered: 11/17/00
Posts: 2342
Loc: West Virginia
Heat rises?

Just a guess...

_________________________
-Virgil
Residential/Commercial Inspector
5 Star Inspections
Member IAEI

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#83071 - 01/08/03 06:57 AM Re: Aluminum Busbar Calculations
JBD Offline
Member

Registered: 07/12/01
Posts: 599
Loc: 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

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#83072 - 01/08/03 02:18 PM Re: Aluminum Busbar Calculations
WARREN1 Offline
Member

Registered: 05/09/01
Posts: 184
Loc: 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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