NEC Table 300.19(A)

[erickench]

If one were to look at the above table you would see something very odd. As the wire sizes get smaller the distances become larger in the same proportion for both copper and aluminum. Here's what I mean:

Size of Wire
2/0 AWG through 4/0 AWG Aluminum 180 ft Copper 80 ft
Over 4/0 AWG through 350 kcmil Aluminum 135 ft Copper 60 ft

80/60=1.3333 135X1.333=180 therefore 80/60=180/135=4/3

But for wires sizes 6 AWG through 1/0 AWG the aluminum distances are 200. It does not increase in proportion. If we were to follow the example above:

Size of Wire
6 AWG through 1/0 AWG Aluminum( ) Copper 100 ft
2/0 AWG through 4/0 AWG Aluminum 180 ft Copper 80 ft

100/80=1.25, 1.25X180=225 feet
This should be the correct distance for Aluminum 6 AWG through 1/0 AWG.

Also, the figure 200 feet for Aluminum 6 AWG through 1/0 AWG is larger than
the figure 100 feet for Aluminum 18 AWG through 8 AWG. How could this be?
The distance for Copper 6 AWG through 1/0 AWG is the same as Copper 18 AWG through 1/0 AWG, i.e. 100 feet. So the aluminum figures should also be the same. Now this for all you engineers out there.:grin: