Figuring voltage drop on this....

[chevyx92]

Do I have this voltage drop calculation correct? Got a little confused here. Situation: We are running a 50A 240V ckt here. Distance from panel to pole #1 is 125' from pole #1 to pole #2 is 260'. Each pole has (4) 1000W MH HID lights contactor controlled. Ballast says 4.5A. If VD= 2KLI/CM (K=12.9-CU) here's what I come up with. VD= 2X12.9X125'X36/16510(#8THHN) = 7.03V That's still under the 3% of 240V. Good so far? Then from pole#1 to pole#2 I get VD= 2X12.9X260'X18/26240(#6 THHN) = 4.6V. Do I have this right or should I have done this calc different? When I first did this I figured the full 385' at 36A but I realized that the distance from the panel to pole#1 has the 36A.

 

[Dennis Alwon]

Do I have this voltage drop calculation correct? Got a little confused here. Situation: We are running a 50A 240V ckt here. Distance from panel to pole #1 is 125' from pole #1 to pole #2 is 260'. Each pole has (4) 1000W MH HID lights contactor controlled. Ballast says 4.5A. If VD= 2KLI/CM (K=12.9-CU) here's what I come up with. VD= 2X12.9X125'X36/16510(#8THHN) = 7.03V That's still under the 3% of 240V. Good so far? Then from pole#1 to pole#2 I get VD= 2X12.9X260'X18/26240(#6 THHN) = 4.6V. Do I have this right or should I have done this calc different? When I first did this I figured the full 385' at 36A but I realized that the distance from the panel to pole#1 has the 36A.

I thnink you got it, at least for single phase. Here's an online vd calculator
http://www.elec-toolbox.com/calculators/voltdrop.htm

 

[RUWired]

Chevyx92, You need to take the total vd allowed (7.2) over the entire run and split it between the segments.With your method, you will have a total vd of 11.63.
Rick

 

[chevyx92]

Chevyx92, You need to take the total vd allowed (7.2) over the entire run and split it between the segments.With your method, you will have a total vd of 11.63.
Rick

I see what you're saying. So then if I use #3 THHN for the 125' run and #6 on the 260' run I would have a TOTAL voltage drop of 6.81v and that's what I need. I thought I got confused on something there. Thanks.