# voltage drop



## elec 1 (Dec 31, 2010)

I know how to do voltage drop calc. for a single load at one location. My question is how to figure wire size for a circuit with multiple loads at several different lengths. I'm guessing I break it down into several calcs. ie. lets say the homerun is 200 feet and the total load is 20 amps so i would calc. then its 200 feet to next load and the load at that point is 18 amps so I would calc. for 18 amps at 400 feet and so on. Am I right?


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## BBQ (Nov 16, 2010)

Yeah you have to figure it 'point to point'.

You have to decide how much VD per run you can live with.

In other words if you could live with 5% drop at the furthest point and there was 5 points you could give up 1% per point. If you had ten points only 0.5% each 

It will never be that easy but I think it gives you the idea.


And of course reduce your load in the calculation as you go.


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## elec 1 (Dec 31, 2010)

Okay so just to be clear if I have 5 legs at100 feet each and 4 amps at each, the first calc would be 20 amps at 100 feet, the second would be 16 amps at 100 feet which is that leg or would it be at 200 feet which is total length at that point.


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## uconduit (Jun 6, 2012)

you're just gonna have to make 5 calculations, 1 for each load


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## BBQ (Nov 16, 2010)

elec 1 said:


> Okay so just to be clear if I have 5 legs at100 feet each and 4 amps at each, the first calc would be 20 amps at 100 feet, the second would be 16 amps at 100 feet which is that leg or would it be at 200 feet which is total length at that point.


100' 

You basically start over at each point using the reduced load and the reduced voltage.


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## RePhase277 (Feb 5, 2008)

I always start with th total load and circuit length to the first point, because often the lingets part of a circuit is the home run. You can get an idea by this voltage drop whether or not figuring the rest of the "elements" is worth doing. The load is continuously decreasing after the first drop.


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## Bbsound (Dec 16, 2011)

Perform what is called a load center calculation, then use that data to calculate voltage drop.


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