DetroitEE
Senior Member
- Location
- Detroit, MI
I was running the numbers on some of my feeders and the voltage drop calculator I usually use seemed to be giving me high numbers. I used another voltage drop calculator to verify my suspicion, and I was right, the voltage drop percentages were too high on the first one. I did a hand calc using the method described on this site, and it was consistant with the numbers to second one was giving me.
Here are my numbers:
208V 3 Phase
1 set of 500kcmil copper
250A load
75 degree conductors
steel conduit
200' run
From a hand calc:
VD = 1.73* 200' * 250A * 12.9 ohms (copper constant) * 1.12 (skin effect) / 500000 (500 kcmil area)
VD = 2.5 V
VD % = 2.5/208 = 1.2 %
Voltage drop calculator 1 is giving me 2.3% (which is wrong) and the second one is giving me 1.1%, which is very close.
This could be user error on my part, but it's not readily apparent to me. Please let me know if you guys see anything which would cause the first one to give me this number. I basically just want to know if the first calculator is programmed incorrectly, so that people will know not to rely one that particular one, and I would notify whoever made the calculator.
Here are my numbers:
208V 3 Phase
1 set of 500kcmil copper
250A load
75 degree conductors
steel conduit
200' run
From a hand calc:
VD = 1.73* 200' * 250A * 12.9 ohms (copper constant) * 1.12 (skin effect) / 500000 (500 kcmil area)
VD = 2.5 V
VD % = 2.5/208 = 1.2 %
Voltage drop calculator 1 is giving me 2.3% (which is wrong) and the second one is giving me 1.1%, which is very close.
This could be user error on my part, but it's not readily apparent to me. Please let me know if you guys see anything which would cause the first one to give me this number. I basically just want to know if the first calculator is programmed incorrectly, so that people will know not to rely one that particular one, and I would notify whoever made the calculator.