Re: [RE-wrenches] fewer wires, mo bettah?

Mon, 20 Sep 2010 17:50:15 -0700

We have done this successfully with a SB6000 and four strings totaling 6.4 and 6.8 kW.

Allan Sindelar
Allan@positiveenergysolar.com
NABCEP Certified Photovoltaic Installer
EE98J Journeyman Electrician
Positive Energy, Inc.
3201 Calle Marie
Santa Fe, New Mexico 87507
505 424-1112
www.positiveenergysolar.com


On 9/20/2010 6:44 PM, North Texas Renewable Energy Inc wrote:
The only potential problem I see might be from one unbalanced string, shading for instance.
Otherwise the 4 <2%r strings feeding back thru a conductor with <1%r should be no problem.
What could possibly go wrong....
Jim
-----Original Message-----
From: [email protected] [mailto:[email protected]]On Behalf Of Hans Frederickson
Sent: Monday, September 20, 2010 6:52 PM
To: 'RE-wrenches'
Subject: Re: [RE-wrenches] fewer wires, mo bettah?

Marco,
In this case, slightly differing resistance between your grounded and ungrounded conductors will not make any difference. You will just need to do your DC voltage drop calculations for each half separately, instead of the typical voltage drop calculation that uses wire length x 2. Different resistance in parallel battery cables is an important issue, but that's not what you're talking about.
 
Regards,
-Hans

 
From: [email protected] [mailto:[email protected]] On Behalf Of Marco Mangelsdorf
Sent: Monday, September 20, 2010 11:08 AM
To: 'RE-wrenches'
Subject: [RE-wrenches] fewer wires, mo bettah?

Check this out.

 

Four series strings of mods on a same plane roof feeding a larger Sunny Boy or Fronius inverter.

 

Four #10 conductors for the ungrounded, fused (at the inverter) conductors.  And for the grounded conductor, a single, common, larger conductor from those four strings.

 

So instead of four pairs of wires, or eight total, I’m using just five (plus ground).

 

Assuming that the larger grounded conductor is adequately sized taking into account conduit fill and temp derate for exposed conduit, does anyone see a problem in doing this?

 

I’ve already been doing this for several years with no problems that I can tell.  But it occurred to me whether different resistances between the ungrounded conductors and the grounded conductor might be an issue.

 

Feedback appreciated.

 

Thanks,

marco

 


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