Voltage drop calculator

ggunn
ggunn Solar Expert Posts: 1,973 ✭✭✭
in Advanced Solar Electric Technical Forum #1
At this site http://www.nooutage.com/vdrop.htm there is a voltage drop calculator, but what I am seeing there is confusing me.

For a three phase 480VAC run of 470 feet and a current of 163A, it tells me that for a double run of 4/0 Cu in steel conduit, I get a 1% Vd, but for a single run I can't get down to 1% even with the maximum conductor size of 750. Does this make sense? From Table 9, 4/0 Cu has a resistance of 0.207 ohms/1000'. To get to half that resistance I only have to go to 500.

Am I missing something?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Voltage drop calculator

    Try a different calculator: http://www.powerstream.com/Wire_Size.htm

    750mil on those specs has a V-drop of 0.39% according to them.
    You can get below 3% with 1/0.

    I've no idea why the difference. Looks like the calc you used is out of whack.
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #3
    Re: Voltage drop calculator
    Cariboocoot wrote: »
    Try a different calculator: http://www.powerstream.com/Wire_Size.htm

    750mil on those specs has a V-drop of 0.39% according to them.
    You can get below 3% with 1/0.

    I've no idea why the difference. Looks like the calc you used is out of whack.
    To confuse things even further, this one http://www.electriciancalculators.com/calculators/vdpfcalculator_initial.html says I need to go to 400 to get to around 1%, while the one you reference says I can get there with 300. If any two of them agreed I'd know what to do.
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #4
    Re: Voltage drop calculator
    ggunn wrote: »
    To confuse things even further, this one http://www.electriciancalculators.com/calculators/vdpfcalculator_initial.html says I need to go to 400 to get to around 1%, while the one you reference says I can get there with 300. If any two of them agreed I'd know what to do.
    It's going to be expensive no matter what, and I want to get it right.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Re: Voltage drop calculator

    If any two of them agreed it'd probably be a sign of the Apocalypse. :p

    The difference may be in conduit (400) or not in conduit (300) as the heat dissipation plays a major role.
    They all tend to have disclaimers about checking with locale AHJ to make sure the plan meets code. Good idea. I'd suggest submitting it with 400 spec'd in conduit.

    Yeah, it's going to be très expensive!
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,658 admin
    #6
    Re: Voltage drop calculator

    Different calculators will make different assumptions with temperature of copper wire. Hot wire, higher resistance.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • YehoshuaAgapao
    YehoshuaAgapao Solar Expert Posts: 280 ✭✭
    #7
    Re: Voltage drop calculator

    I like http://www.electriciancalculators.com/ , especially the VB app, though at higher temperatures you are stuck with a javascript version as the VB version starts going in steps of 10 and rounds everything pessimistic (the code book keeps going in steps of 5).

    http://www.electriciancalculators.com/ sticks to the code book as much is possible. Where it deviates, it rounds pessimistically (bigger wire)
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #8
    Re: Voltage drop calculator

    Or, if you have not installed the conduit yet, go up 2 sizes, and use aluminum wire, much easier to pull, (but don't forget the anti-ox goop) .
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