malachi constant
Senior Member
- Location
- Minneapolis
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!
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!