Voltage drop calculation

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l3city

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Hi there!
When calculating voltage drop, is it required to consider the whole feeder/branch circuit length or is it permissible to consider half way the feeder/branch circuit length in the calculation?:smile:
 
I don't understand the question. Current will flow through the entire length, and voltage will be dropped along the entire length. I do know that the formulas are sometimes confusing, when it comes to length. You need to make sure you are using the "one way length" or the "round trip length," as is required by the formula you are using.
 
I think the op is asking if he needs to consider the feeder that supplies the panel that the branch circuit is fed as well as the length of the branch circuit. If this is correct then I would say you should consider the entire run.
 
l3city said:
Hi there!
When calculating voltage drop, is it required to consider the whole feeder/branch circuit length or is it permissible to consider half way the feeder/branch circuit length in the calculation?:smile:
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If you have branches and taps off of the cuircuit then you can calcualte the voltage drop for each segment separately.

Ex. 1200ft feeder has a 600A load at the source.
Has a 50A branch at 200', has a 200A tap at 500' and another 200A branch at 800'.

Frist 200' is sized to 600A,
next 300' is sized to 550A,
next 300' is sized to 350A and the last segment is sized to 150A.

Just remember that the total drop should not exceed 3/5 percent, depends on whether it is consdiered as a distribution system with branches or not. At each new point you have to start with not the full voltage but the reduced voltage that the previous segment caused.
 
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