I am going to a electrical tech school. We are now working on calculating wire sizes and such. I want to make sure that I am doing this correctly so I am going to post some sample problems and my answers so you all can check my work. I apprieciate any tips.
1) 25 #12AWG copper cunductors type THHN, in conduit. The ambient temp is 95*F What is the ampacity of each conductor?
A:the chart lists #12 copper THHN @30
the correction factor is 0.96 for 95*
so 30(0.96)=28.8A
then 50% correction for 25 in conduit
so 0.96(0.50)=14.4A
2) a single phase load is 2800' from the source and draws a current of 86A, and operates at 480V. Maximum voltage drop must not exceed 3%. What size of Aluminum conductor should be used?
A: 480V(3%)=14.4V
R=14.4V/86A
R=0.167
CM=(K)L/R
CM=(17)2800/0.167
CM=285,030
the closest size is 300Kcmil
3) A 3 phase motor operates on a 480V and is located 1800' from the source. Current is at 235A. Using copper voltage drop not to exceed 6%
A: 480V(0.06)=28.8V
L= 1800(1.732)=3118
CM=10.4(3118)/0.123
CM= 263,636
all 3 shall be 300Kcmil
Sorry if these formulas are unclear.
Thanks for any help
MW
