Triplex calculations

[johnson]

I'm nunclear on triplex load calculations.
For example Table 310.7 shows 1/0 aluminum at 75 degrees C to have an ampacity of 180 amps.
Industry charts show a value of 200 amps.
Table 9 shows resistance of 0.20 or 0.21 ohms but all values in this table are based on 3 conductors in conduit. Table 8 shows circular mil of 105,600.

Fully loaded (by NEC) this wire will only care rated current for 100 feet before getting over 3% voltage drop. When 80% loaded it still can only go 125 feet.

Is this right? Somehow it seems like it should be further. Where are resistance values located for aerial conductors? Surely the utilities aren't using these values. Any comments?

 

[bbeste]

Re: Triplex calculations

Well lets give it try. On 1/0 acsr (Code name Raven) it is rated for 235 amps in free air.Keep in mind this is bare wire . Looking at the chart in the book it appears to me that the triplex version of this is 180 amps(That would be 2 coated hot legs and one bare neautral. The way I figure voltage drop is Voltage drop = amps X Legenth X 2(ac voltage has to travel there and back)X Resistance per 1000'divided by 1000. Resistance per 1000' on 1/0 aluminum is .1612.
RxLx2x(R per 1000')/ 1000= voltage drop.

Hope I did not confuse you to bad.
Barry