Big Wire? [RE-wrenches]

Joel Davidson joeldavidson at earthlink.net
Thu Apr 15 19:01:23 PDT 2004


 

===========================================================
$6.95 .com Domain Name Sale! 
Limited Time! ICANN Accredited GoDaddy! 
http://click.topica.com/caab8Lhbz8Qcsbz9JC9a/ GoDaddy
===========================================================

Hello Ray,
PV costs are down, but wire is still cheaper than voltage drop. Even a small
percentage of energy lost over the life of a PV system can add up whereas
wire is a one-time cost. As a percentage of system cost, wire is not a place
to economize. Also, old copper wires are recycled. Sometimes, sad to say,
new copper wire is stolen and recycled.
Best regards,
Joel Davidson

----- Original Message ----- 
From: "Ray Walters" <ray at solarray.com>
To: <RE-wrenches at topica.com>
Sent: Wednesday, April 14, 2004 1:55 PM
Subject: Big Wire? [RE-wrenches]




===========================================================
Your opinion counts! We're conducting a survey for a
computer service/repair company. When you complete our
survey, you will also be entered into a drawing for one of
ten $100 prizes. Just click
http://click.topica.com/caab8K4bz8Qcsbc0WJAa/ Val Rad
===========================================================
Hey All;

I have been studying for the NABCEP exam, and for voltage drop
calculations, they dictate using Table 8 of the NEC book, with the classic
2% loss. I found the NEC table to be overly conservative and it doesn't
take into account what total % ampacity you are running the wire at, or
temperature. For PV array to load center wire sizing, I use a formula that
uses circular mils and has  a lower resistance factor if the wire is being
run at less than 50% of its ampacity. This formula seems to correspond well
with actual field measurements also.  What are my fellow Wrenches using
these days?

Next, instead of converting voltage drop to a percentage, I multiply it by
the current to get total watts lost. I multiply the watts being burned as
heat by the cost of an installed PV watt (say $6.00). This gives me an
actual dollar figure of what the volt drop is costing us. Basically, I
compare 2 to 3 likely wire sizes and costs, and pick the wire that is the
most cost effective ( of course I back check it for ampacity  against the
NEC book). Many times blindly sizing for a 2% volt drop just doesn't make
sense. PV costs are down, while copper prices are rising fast. Why spend an
additional $300 for larger cable when you may be only netting another 20
watts of power ($120 value)? Besides being more cost effective, this sizing
method reduces our use of  copper, which anyone who has seen a copper strip
mine knows is a good thing.
Any comments or criticisms on this method?  Try the calcs yourself next
time, you'll be amazed how quickly the point of diminishing returns
approaches. Use retail installed costs for both the PV and the wire and
conduit. Remember that bigger wire takes longer to pull and connect.  By
the way this method assumes an MPPT controller, with a regular controller
your power savings from over sizing wire are even less.


Ray Walters

===========================================================
$6.95 .com Domain Name Sale!
Limited Time! ICANN Accredited GoDaddy!
http://click.topica.com/caab7pQbz8Qcsbc0WJAf/ GoDaddy
===========================================================

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

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

List rules & etiquette: www.mrsharkey.com/wrenches/etiquete.htm

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

Hosted by Home Power magazine

Moderator: michael.welch at homepower.com

===========================================================
$6.95 .com Domain Name Sale! 
Limited Time! ICANN Accredited GoDaddy! 
http://click.topica.com/caab7pQbz8Qcsbz9JC9f/ GoDaddy
===========================================================

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

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

List rules & etiquette: www.mrsharkey.com/wrenches/etiquete.htm

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

Hosted by Home Power magazine

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

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
--^----------------------------------------------------------------








More information about the RE-wrenches mailing list