wire sizing at Higher voltages [RE-wrenches]

[Ray Walters]

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>  Hi Jay;

If your going 100 ft at a current of 15 amps, #10 will have a power loss of 
15x15x 200ft x 1.02Ohms/ 1000 ft = 54 watts.
a #6 wire will have a power loss of 15 x15x200 ft x .403 ohms/ 1000 ft 
=  18 watts. We just saved 54 -18= 36 watts.
At $6/ watt for PV, that was worth $216.00.  If #6 is 30 cents more per ft. 
that's $60 extra for 36 watts or $1.66/ watt .

a #4 wire will have a power loss of 11 watts, therefore we could save 
another $42 of power. So if #4 is less than 21 cents per ft more expensive 
than the #6, it might be worth it. At higher currents it becomes an easier 
choice.
On PV its power drop, not voltage drop.

Ray


>Hi Ray,
>
>I'm curious about just how far are you trying to run this wire? #4 using a
>SMA?
>
>And what voltage drop are you trying to get?
>
>thanks,
>jay
>
>Peltz Power
>
>----- Original Message -----
>From: "Ray Walters" <ray at solarray.com>
>To: <RE-wrenches at topica.com>
>Sent: Tuesday, April 20, 2004 5:05 PM
>Subject: Re: wire sizing at Higher voltages [RE-wrenches]
>
>
> >
> >
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> >
> > HI Joel, Ron, & all;
> >
> > Seems like the terminals should go up to a #4 Ga, if SMA's recommendation
> > is to size for less than 1%. The reason I asked in the first place is that
> > extra splices to land an oversized wire on small lugs cost extra money and
> > eats into our savings from over sizing in the first place.
> > Ron, I'm glad I'm not the only one sizing for power drop. I got into it
> > years ago when the cost of keeping to a 2% volt drop on 12 volt systems
>was
> > getting outrageous. (200 watt array on 2/0 cable??) I had to convince
> > myself before I could convince my customers that it was worth it.( It
> > wasn't) I have some arrays on non MPPT controllers and we're letting volt
> > drop go as high as 10%. It just wasn't cost effective, and without MPPT
>you
> > don't really see that extra power anyway.
> > Another funny thing that came out of the calculations I was doing: it
> > didn't matter how short the run was. If you could save 1 watt on a 5 ft
>run
> > by oversizing it, it was worth it. (Not of course if the lugs or conduit
> > can't take it)
> >
> > Sincerely,
> > Ray
> >
> >
> >
> > >Ray,
> > >Interesting discussion. From the SMA web site:
> > >  SMA America recommends sizing the PV wired to keep the voltage drop
> > >below 1%.
> > >  In
> > >any case, the DC terminals in the Sunny Boy Inverter will only accept up
>to
> > >10 AWG wire.
> > >Best regards,
> > >Joel Davidson
> >
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