[RE-wrenches] DC conductor line loss numbers

[William Miller]

I have worked out the area under the daily bell curve. A 2% loss at max current equals 1% loss average. Maybe this logic could allow some flexibility. 

William



> On Jul 25, 2015, at 5:52 AM, Jerry Shafer <jerrysgarage01 at gmail.com> wrote:
> 
> Wrenches
> I have 3 engineering firms and one in-house engineer that only use 1% because in the NEC it is stated as a suggestion and not a requirement but they take this as a must not exceed instead, 
> I cant change CC as it will be remotely monitored via the Outback connection, the Engineers refuse to make any changes to the 1% and still stamp the drawings. This is what I have found in my research it came from Mike Holt
>  
> Contrary to common belief, the NEC generally doesn't require you to size conductors to accommodate voltage drop. It merely suggests in the Fine Print Notes to 210.19(A), 215.2(A)(4), 230.31(C), and 310.15(A)(1) that you adjust for voltage drop when sizing conductors. It's important for you to remember that Fine Print Notes are recommendations, not requirements [90.5(C)].
> 
> The NEC recommends that the maximum combined voltage drop for both the feeder and branch circuit shouldn't exceed 5%, and the maximum on the feeder or branch circuit shouldn't exceed 3%. This recommendation is a performance issue, not a safety issue.
> 
> Jerry
> 
> 
>> On Wed, Jul 22, 2015 at 11:28 AM, Starlight Solar Power Systems <larry at starlightsolar.com> wrote:
>> Jerry,
>> 
>> A long distance wire run is practical now days using a high voltage controller. Have a look at Schneider and Morningstar 600Vdc controllers. Not sure what you mean "by nothing can be changed but wire size” but you will have to rewire the strings into series and protect the wire run.
>> 
>> Larry Crutcher
>> Starlight Solar Power Systems
>> 
>> 
>> 
>> On Jul 22, 2015, at 10:37 AM, Jerry Shafer <jerrysgarage01 at gmail.com> wrote:
>> 
>> Wrenches
>> Some time back there was discussion on the conductor size and efficiency rating requirement for long DC runs.
>> What I am looking at is this, 400 feet of MCM 400 to keep the line loss at or below 1% per NEC code for an off grid application, cost vs return is not acceptable. 2/0 is less than 2.5% and the cost is far less. Specs are 4 strings of 3, 250 watt modules feeding one Outback FM 80 charge controller. There are lots of things I can do like SMA instread, or 200 VDC charge controller but nothing can be changed except the wire gauge. Does anyone recall a thread with this topic.
>> 
>> thoughts ??
>> Jerry
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