Voltage Drop Across a Distance

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Solar Noob

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Electrical Engineering (in training)
I am having trouble finding how to calculate the voltage drop across a distance. I have seen a ton of different formulas, but for the most part I am not sure where to start. The equation I found that seems the best is VD = 2 * I * L (in feet) * (R (ohms/1000ft)/1000). I was having trouble finding the resistance, and there are a ton of tables online that use different resistance values.

The main question I have is what is the best way to calculate voltage drop based off of NEC standards, and where do I find the information to perform the calculations on my own?
 
Solar Noob said:
I am having trouble finding how to calculate the voltage drop across a distance. I have seen a ton of different formulas, but for the most part I am not sure where to start. The equation I found that seems the best is VD = 2 * I * L (in feet) * (R (ohms/1000ft)/1000). I was having trouble finding the resistance, and there are a ton of tables online that use different resistance values.

The main question I have is what is the best way to calculate voltage drop based off of NEC standards, and where do I find the information to perform the calculations on my own?
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For single phase. VD = 2 * L * R * I / 1,000 You can get the resistance of uncoated copper from chapter nine table 8.
 
For NEC use, grab table 8 of chapter 9 of the NEC, and use the 'DC resistance' of the conductor in question as an acceptable approximation.

The table gives R in ohms per 1000 feet of conductor. So you need to use a length unit of 1000 feet to get the numbers to work right.

Using your selected equation, imagine you have a 5A load flowing on 12ga circuit that is 150 feet from source to load:
VD = 2 * 5A * 150(ft) / 1000 * 1.93Ohm/1000(ft) = 2.9V

-Jon
 
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