area of aluminum conductors

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malachi constant

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NEC Chapter 9, Table 5 lists approximate areas of varying conductors. For instance, XHHW #250 is 0.3904 in^2. This table does not distinguish between aluminum and copper conductors.

I have an Excel spreadsheet feeder schedule put together ten years ago by an engineer much smarter than I. It contains wire area tables for both CU and AL - and they are different. The CU tables match the NEC tables value for value. The AL tables contain smaller values - for instance XHHW #250 AL is 0.3421 in^2. I have not been able to verify where these values came from. Anyone know if AL is slightly smaller than CU - are these are valid? This guy was sharp as a tack, I would be very surprised if he was wrong.

So you don't have to guess why I'm asking... One of our engineers missed a ground wire from a generator - sized it as a separately derived service. The conduit is in the ground, but the (aluminum) feeders aren't yet pulled. If I add up the standard Chapter 9 Table 5 values, and compare them to the applicable Table 4 "Over 2 Wires 40%" column, it just barely doesn't fit. If I use the "smarter engineer than me" values for aluminum wires, it does fit. I would really like for his numbers to be valid. There are multiple parallel feeders running about 100'.

If this doesn't work what are your thoughts on these other options?: (1) Add a parallel feeder, (2) use copper instead of aluminum, or (3) use compact aluminum conductors. Each of these would work - I think (1) and (2) are roughly the same cost (~$15K!), but can't find any cost data on compact conductors. Nor do I know anything about them, other than they would fit.

Any thoughts are appreciated. Thanks!
 
Take a look at Table 5(A). It appears his AL measurements are for compact aluminum conductors.
He might still hold his "sharp as a tack" title :D
 
maybe he measured them for what he was actually using.

are you required to use the values in the table or can you use what they really are?
 
There are several different styles of stranded wires which all have different actual cross sectional areas even though they share a nominal size.

Normal construction uses several small round conductors in a general overlay wrap. This is the one most people think of when they imagine stranded circuit wire. There is a notable amount of air gaps betweeen the individual strands.

There is a related construction that uses smaller individual conductors and yet results in an overall larger bundle. This is usually found in the really flexible conductors like 'welding cable'.

Aluminum has the ability to deform a little more than copper does, so the standard overlay construction can be squeezed, thereby making the gaps between the stranding much smaller which reduces the overall conductor diameter, while the amount of metal remains pretty much the same (in some cases these are comparable to their copper equivalent).

Finally, it is very easy to extrude the small aluminum strands into non round shapes (think of pie shaped wedges) while they are being made. These formed conductors can then be wound together with almost no air gap around them, resulting in a very compact conductor (in some cases these could be smaller than their copper equivalent).
 
NEC Chapter 9, Table 5 cross section includes insulation, too. UL 1581 also, does not separate any conductor of copper aluminum and copper-clad aluminum and UL 44 does not provide different insulation for copper or aluminum conductors. I think the difference is produced only due to how the conductor was stranded: concentric round, compressed or compacted- as augie47 already said.:slaphead:
 
Almost all aluminum conductor that I have used for several years is compact conductors. Some URD cables are not, but even many of the most popular sizes of those seem to be compact conductor as well. All XHHW I ever recall using for a very long time has always been compact conductors.
 
kwired said:
Almost all aluminum conductor that I have used for several years is compact conductors. Some URD cables are not, but even many of the most popular sizes of those seem to be compact conductor as well. All XHHW I ever recall using for a very long time has always been compact conductors.
Click to expand...

i don't know if they even make "uncompacted" aluminum conductors any more.

hypress dies and lugs are different for each....

*rest of comment deleted to avoid appearing stupid.*:dunce:
 
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Fulthrotl said:
i don't know if they even make "uncompacted" aluminum conductors any more.

hypress dies and lugs are different for each....

*rest of comment deleted to avoid appearing stupid.*:dunce:
Click to expand...
Sure delete what I was about to make you look like a fool about, I hit "reply to post" and then something different came up then what I was reading before:)
 
thanks all!

thanks all!

The contractor sent me information on the cables he is using. They are indeed compact. The ground fits. The older smarter engineer is correct again (thank goodness)!!
 
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