OH MY GOD!!!! I just woke up, read the news on MSN about Rita, checked out this post and WOW!!! You east coasters have been very busy!!!
With half closed eyes and only one downed soda I'll try to answer some of these posts.
Tripp, I ran your info through Volts with nice results. I assumed a load of 75A as this is the max for #4 Al and #6 Cu conductors. I used the Earth(buried) raceway selection at 60ºF for the Al and PVC Schedule 80 at 105ºF for the Cu. I also assumed 208V, 3 phase.
Impedances computed at .02571... for Al and .05566... for Cu. Totaling at .08137... for the 127' total run. Using Vd = I * R and %Vd = Vd / V, I computed a 2.93 % Vd for the total run.
Gad, it's still to early for me and these numbers!
Joe, Volts automatically adjusts the ground conductors per 250.122 when increasing or decreasing conductors.
I'm sorry but I forgot the name of the gentleman using real and imagionary(j) numbers. I'm not going to double check your figures but I am very impressed!!! Volts does use similar formula for computing sin wave distruction in busbars.
And for the gentleman who stated that these types of formulae are okay to use in software...That's the point of using software in place of quick rule of thumb formula. I used to compute VD by hand using "IEEE Std 141 Exact Formule" and it drove me nuts, especially when a change was made and I had to redo everything again, and again.
And NEC only suggests and does not enforce VD. However, since ambient temperature is a major contributor to VD, the NEC included the temperature Correction Factors to adjust the conductor size accordingly.
I hope that I didn't leave much out, but I need another soda and some more wakeup time.
[This message has been edited by DiverDan (edited 09-24-2005).]
