[RE Marketing] 400 ft DC voltage drop [RE-wrenches]

[Ray Walters]

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My spread sheet sizer uses the NEC formulas and uses their temp.  
corrections as well. You can input both ambient and conductor temps.
Contact me off list if you want a copy.

ray at solarray.com


On May 1, 2008, at 7:41 AM, Tom DeBates wrote:

>
> good day Wrenches,
>   I have used NEC Chapter 9, Table 8 for DC conductor resistance and
> have noticed that the data is for conductors @ 75C. Since most of  
> these
> "runs" would be below grade, wouldn't the conductor temp be lower  
> (~20C
> ?) I see that Note #2 has a correction factor, but I've always been  
> too
> lazy to try it. Has anyone done this and, if so, has it made much of a
> difference?
> thanks,
> Tom
> Jeff Clearwater, Village Power Design wrote:
>>
>> Hi Steve,
>>
>> William' approach is exactly it.  We use to do 1% at Vmp but as
>> copper prices increased we did a more careful analysis of the peak vs
>> average issue and now use 1.5%  But as he says make sure that's from
>> panel to inverter, not just from combiner to disconnect.  I do take a
>> look at Vmin (the inverter's MPPT min) for the worst case scenario
>> but that usually doesn't go over 2% if Vmp is at 1.5% or better.
>>
>> That said if the run is short or the pull easy I tend to bump up a
>> size to maximize those precious PV watts which usually puts me back
>> in the 1% range at Vmp - but if the run is long and the cost starts
>> going up - William's perspective is what we use.
>>
>> Hope that helps!
>>
>> Jeff Clearwater
>> Village Power Design
>>
>>
>>> Steve:
>>>
>>> I'd say E because high temp Emp will occur at lower output amperage.
>>> I doubt the difference between D or E will be significant and Voc
>>> does not count.
>>>
>>> Consider this concept:  Rated current occurs rarely, if ever.
>>> Assume, though, it occurs at noon.  The rest of the day presents
>>> varying degrees of lesser current.  What is the area under the
>>> curve?  My research indicates it is 50% of the peak amperage.
>>>
>>> What does this mean?  It means that if you design a PV feeder for 2%
>>> voltage drop at peak output, it will average 1% over the day.  Or,
>>> design criteria for PV feeders is only half as important as we think
>>> it is.  (Don't forget to quantify cumulative loses throughout all
>>> feeders and components, however.)
>>>
>>> William Miller
>>>
>>>
>>> At 10:18 PM 4/30/2008, you wrote:
>>>> I have a 400 foot run on an output circuit to combiner, 23.5 amps.
>>>> Should the DC VOLTAGE that is used as the system voltage to  
>>>> calculate
>>>> voltage drop be:
>>>> A) Voc at low temperature
>>>> B) Voc at high temperature
>>>> C) Nameplate Voc
>>>> D) Vmp at high Temperature
>>>> E) Nameplate Vmp
>>>>
>>>
>>
>>
>> -- 
>> ~~~~~~~~~~~~~
>> Jeff Clearwater
>> Village Power Design
>> Sustainable Energy & Water Solutions for Home & Village
>> http://www.villagepower.com
>> gosolar at villagepower.com
>> NABCEP (tm) Certified Solar PV Installer
>>
>> Voice: 413-259-3776
>> Fax: 413-825-0703
>> 65 Schoolhouse Rd
>> Amherst, MA 01002
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~`~
>
>
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R. Walters
Solarray.com
NABCEP # 04170442	




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