changing conductor size in voltage drop

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i have a question - can i run 200ft of #6 from a panel to a box and change over to 100ft of#10 to a 10amp 120v load on a 20amp breaker - if i stay at 3% vd i need to keep the #10s. If this is incorrect please let me know the vd calc. I am a long time reader of this forum and a 1st time poster so go easy on me. thank you
 

infinity

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Yes, you can mix and match conductor sizes for VD compensation. It doesn't matter where in the run you use the larger conductors and the 3% is a good design issue but it's not mandatory.
 

RUWired

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thank you so i did the calc. right i did the 2 vd calc. and added the % together.
You need to review the # 10 awg at 100'(2.48 VD). I see using # 8 awg for the 100'(1.56 VD). Along with the # 6 awg (1.96 VD) + (1.56 VD) = 3.52 total VD.

Rick
 

infinity

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You need to review the # 10 awg at 100'(2.48 VD). I see using # 8 awg for the 100'(1.56 VD). Along with the # 6 awg (1.96 VD) + (1.56 VD) = 3.52 total VD.

Rick

Are these numbers volts or percentages? Would you find the voltage drop in volts for each section, add them together and then compare that to the applied voltage or am I off on a tangent somewhere?
 

RUWired

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Location
Pa.
Are these numbers volts or percentages? Would you find the voltage drop in volts for each section, add them together and then compare that to the applied voltage or am I off on a tangent somewhere?
(voltage dropped) I added each section for a combined total vd of 3.52 volts dropped. With the OP. i came up with a combined total of 4.44 which would be over the 3.6 VD recommended.

Rick
 
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kingpb

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Formula would be:

VD (volts) = 2*I[L1R1 + L2R2]/1000

= 2 *10 [200*0.49 + 100*1.2]/1000

= 4.36V

VD% = (4.36/120) * 100

= 3.6%

Using a #8 instead of a number #10 improves the VD to 2.9%.

Using a #8 for the whole distance is 3.9% drop, but it saves the j-box, etc.
Unless your starting a motor, I'd take the easier install and go with #8 the whole distance.
 

Dennis Alwon

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Depending on the type of load 4.4 volt drop may not mean much esp. since the voltage is generally higher than 120V to begin with. 3% is a recommendation not a code issue.
 
I have to keep the #10s there all ran &connected already & the max VD is 5% I just rather keep it close to 3% that's why I figured the #6s. Thanks for the replys.
 
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