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cu free air amps vs cu enclosed


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coolen 
Copper - Posts: 121
Copper spacespace
Joined: October 27, 2008
Location: Nova Scotia, Canada
Posted: August 19, 2010 at 8:24 PM / IP Logged  

I was looking at this chart: http://wiki.xtronics.com/index.php/Wire-Gauge_Ampacity#Load_Carrying_Capacities_or_Ampacities, and noticed the difference between the "CU free air amps", and the "CU enclosed amps".  I'm more  curious about the 8awg wire as I have intentions in running it to power a fuse block.

Does it mean when it refers to free air, that the wire is used as a primary power by itself, and enclosed means when it is part of a "run of wires", or as multipule conductors in a conduit,  for example a 8/2 .

From the information that I have gathered on this site, I should be safe to use a 8awg power wire to power a  block up to 100 amps. Is this correct?

Thanks

oldspark 
Gold - Posts: 4,913
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: August 20, 2010 at 4:05 AM / IP Logged  
I'll bow to others with better experience....
As I read it, for 100A you want 6AWG free-air or 2AWG enclosed.
Else 2 x 8AWG (for only 92A enclosed).
"Enclosed" is vague, but in this case I interpret it as a single conductor with non-circulating air. But that shouldn't be much different to bundled etc - the point being "no conduction of convection" of heat.
That's at 20°C and generous - stranded and annealed will have lower capacities.
i am an idiot 
Platinum - Posts: 13,666
Platinum spaceThis member consistently provides reliable informationspace
Joined: September 21, 2006
Location: Louisiana, United States
Posted: August 20, 2010 at 7:14 AM / IP Logged  
You must use insulated wire in your car.  This chart is useless for this application.  Copper will dissapate more heat if it is not insulated.  You should not use uninsulated wire in your car.
oldspark 
Gold - Posts: 4,913
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: August 20, 2010 at 8:33 AM / IP Logged  
Interesting. Whilst I agree with you (d'oh!!), I interpret that table as being insulated Cu (just suspended in "free air").
But IMO it is another example of underspecification which is generally dangerous.
However I caution everyone to the top disclaimer... "It is not permissible to be read by anyone who has ever met a lawyer. Use is confined to Engineers with more than 370 course hours of electronic engineering for theoretical studies."
(Though I think they forgot the negation in "...anyone who has Never met a lawyer...."

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