[RE-wrenches] DC conductor line loss numbers

[Glenn Burt]

You would want to confirm hot temp PV circuit values with chosen Vdrop to ensure the irrelevant value doesn't drop you out of the inverters' operational limit, however.

Sincerely,
Glenn Burt
Sent from my 'smart' phone so please excuse grammar and typos.

-----Original Message-----
From: "Chris Mason" <cometenergysystems at gmail.com>
Sent: ‎7/‎25/‎2015 15:20
To: "RE-wrenches" <re-wrenches at lists.re-wrenches.org>
Subject: Re: [RE-wrenches] DC conductor line loss numbers

It should be noted that the NEC recommendations for feeder circuits are to
do with acceptable voltages at the load, i.e., you do not want your 208V
equipment running on 200V. PV circuits are not feeder circuits, voltage
drop is irrelevant. Power loss may be relevant, but only in terms of
economic value. If it is preferable to add more PV and lose 10% of the
power, as long as there are no issues of heat and potential fire, why
shouldn't you be able to make that decision? As PV gets cheaper, replacing
cables costing $10,000 to save $10 a year does not make sense. The NEC
rules on voltage drop were never designed for PV source circuits.

On Fri, Jul 24, 2015 at 11:52 PM, 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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-- 
Chris Mason
NABCEP Certified Solar PV Installer™
Solar Design Engineer
Generac Generators Industrial technician

www.cometsolar.com <http://www.cometenergysystems.com>
264.235.5670
869.662.5670
Skype: netconcepts


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