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1. Senior Member
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## V.D.

Hi
I have a sub panel-A that is 60 feet away / run from source
and sub feed to another sub panel-B 20 feet away away/run

Question is ;
For calculating of V.D of panel-B , I should consider the feeder length 20 feet or 60+20=80 feet

??????
Thank you

2. gar
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180311-1212 EDT

Calculate voltage drop from source to panel A, separately calculate voltage drop from panel A to panel B. Add these two together. Your currents and conductor sizes are unlikely to be the same. Thus, the need for two different calculations. If the current and conductor sizes were the same from end to end, then you would just use total length.

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3. Originally Posted by gar
180311-1212 EDT

Calculate voltage drop from source to panel A, separately calculate voltage drop from panel A to panel B. Add these two together. Your currents and conductor sizes are unlikely to be the same. Thus, the need for two different calculations. If the current and conductor sizes were the same from end to end, then you would just use total length.

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Can't just add them arithmetically as a rule.

4. gar
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180311-1338 EDT

Besoeker:

True, but I doubt it would make any difference to Toros so I tried to be as simple as it might apply to his question.

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5. First segment of this will carry 100% of the load. Calculate VD for that segment based on total load of both panels.

Calculate second segment based on load of panel B, but remember you already had some drop at panel A, so if you have 120 volts at source, and calculate a 1 volt drop at panel A, and 2 volts drop on feed to panel B, that means you will have 119 volts at A and 117 volts at B.

VD calculations are typically based on nominal voltage though, it is possible you actually start out with maybe 123 volts from the source.

6. Originally Posted by gar
180311-1338 EDT

Besoeker:

True, but I doubt it would make any difference to Toros so I tried to be as simple as it might apply to his question.

.
Good point.

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