I have read other threads concerning this question but It still wasn't made clear to me.

Say you have a load connected in parallel 50 feet from the source. The code recommends not more than a 3% voltage drop in a branch CIRCUIT, that is to say out and back, so in calculating the R portion of VD=IR you would use 100 feet. 50 feet out to the load and 50 feet back to the breaker.

__My question is__, Why does the voltage drop on the line RETURNING from the load matter? wouldn't you only be concerned with the voltage SUPPLYING the load?

I have theories as to why the Out and Back length is used as opposed to the one way length.

It might have something to do with the rules for "E" in a parallel circuit; the voltage across one load is equal to the total voltage of the circuit. But even knowing that I'm not sure how that works.

I'm coming at it from the perspective of the load, if it gets enough voltage coming to it, it will work properly. How would the voltage lost after it went across the load matter?

**Also,**? would you still have to double the one way distance for a series circuit?

I'm unclear as to what you mean by parallel versus series in your questions.

For the following circuit: hot to black wire, black wire 50 feet, load, white wire 50 feet, white to neutral, you really have 3 resistances in series: the black wire, the load, and the white wire. It is reasonable to assume the same resistance for the black wire and the white wire (assuming they are the same size and same length), so you double the voltage drop of one to make the calculation simpler.

The voltage drop in the black wire (E = I*R) and the voltage drop in the white wire are added together to determine the voltage drop to the load VDblack + VDwhite = VDtotal (which is the same as doubling one value). The voltage at the load is Voriginal - VDtotal.

If you were to measure the voltage difference between the beginning of the black wire and its end, then measure the same for the white wire beginning to end, you would see that they are the same. In the same way if you measure the voltage across the line at the beginning of the black and white wires and compare that reading with the voltage between the black and white wires at the load, you would see the difference was 2*VD in one wire.

There is nothing magic about the white wire.

If you don't already have an "Uglies" electrical handbook, I recommend you get one. It should be available at one or more of the electrical wholesalers in you area, or you can order one from Amazon. It is chocked full of useful information and the first section will help you with calculations like this.

If you will explain your parallel versus series circuits, I'll address them.