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

[Walt Ratterman]

Hello all,

Actually, I used the formula, and re-wrote all of the VD tables to correct
for a HIGHER temperature, because it is rare that the conductors will be at
room temperature, at least where I work.  True, portions of our DC homeruns
are often underground, but often not, and then there are all of the cables
on the panels that are at quite elevated temperatures.  This correction has
usually, but not always, increased my wire sizes 1 AWG or MM wire size above
what is often recommended in the tables.

Walt
SunEnergy Power International

-----Original Message-----
From: Tom DeBates [mailto:habitek83 at yahoo.com] 
Sent: Thursday, May 01, 2008 6:41 AM
To: RE-wrenches at topica.com
Subject: RE: [RE Marketing] 400 ft DC voltage drop [RE-wrenches]


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
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~`~


- - - -
Hosted by Home Power magazine

To send a message: RE-wrenches at topica.com

Archive of previous messages: http://lists.topica.com/lists/RE-wrenches/read

List rules & how to change your email address:
www.mrsharkey.com/wrenches/etiquette.php

Check out participant bios: www.mrsharkey.com/wrenches/

Moderator: michael.welch at homepower.com



__________ Information from ESET NOD32 Antivirus, version of virus signature
database 3068 (20080501) __________

The message was checked by ESET NOD32 Antivirus.

http://www.eset.com


- - - -
Hosted by Home Power magazine

To send a message: RE-wrenches at topica.com

Archive of previous messages: http://lists.topica.com/lists/RE-wrenches/read

List rules & how to change your email address: www.mrsharkey.com/wrenches/etiquette.php

Check out participant bios: www.mrsharkey.com/wrenches/

Moderator: michael.welch at homepower.com
--^----------------------------------------------------------------
This email was sent to: michael.welch at re-wrenches.org

EASY UNSUBSCRIBE click here: http://topica.com/u/?bz8Qcs.bz9JC9.bWljaGFl
Or send an email to: RE-wrenches-unsubscribe at topica.com

For Topica's complete suite of email marketing solutions visit:
http://www.topica.com/?p=TEXFOOTER
--^----------------------------------------------------------------