[RE-wrenches] Parallel wire runs to increase size

[Starlight Solar, Larry Crutcher]

Dan and others, 
Thanks for the comments. The answer from Dan is what I was needing: 
"For two parallel runs of different sized conductors, add the circular mil area for both conductors, then using a wire table (such as a pocket guide), find the gauge closest to the total CMA to get the AWG equivalent."

Perhaps I should have explained that the PV system voltage is under 50 volts and that all conductors are bonded with terminal blocks at both ends. The current will distribute itself across the two conductors.

Just a side note for those concerned with the NEC and RV wiring: After years of wire installations in nearly every recreational vehicle made, I can assure you that not one RV is in total compliance with NEC. Some of the DC wiring performed by manufacturers is downright dangerous with long cable runs or many branch circuits with no circuit protection at all. Very scary. 

Larry
  ----- Original Message ----- 
  From: Exeltech 
  To: RE-wrenches 
  Sent: Wednesday, February 02, 2011 10:26 AM
  Subject: Re: [RE-wrenches] Parallel wire runs to increase size


        NEC 310.4 permits parallel conductors of 1/0 or larger.  Conductors smaller than 1/0 are permitted, but with stipulations.

        Nick's assertion "most if not all of the current will flow on the larger wires" is incorrect. The current will be shared proportionately between two paralleled conductors commensurate with their individual resistances.

        The original query related to recreational vehicle PV DC-side installation, and referenced installation of a "second PV", implying only one existed initially.  This would thus fall outside the bounds of the NEC, but shouldn't be interpreted to mean some of the common-sense aspects of the NEC aren't to be considered.

        Dan



        --- On Wed, 2/2/11, Jason Szumlanski <Jason at fafcosolar.com> wrote:


          From: Jason Szumlanski <Jason at fafcosolar.com>
          Subject: Re: [RE-wrenches] Parallel wire runs to increase size
          To: "RE-wrenches" <re-wrenches at lists.re-wrenches.org>
          Date: Wednesday, February 2, 2011, 11:15 AM


          Nick,



          Can you cite a code section that supports this. (not challenging you – it makes sense and I agree)



          I have been wondering about SMA’s recommendation to parallel two 1/0 cables for a Sunny Island. If the wire sizes and lengths are identical, is this acceptable?



          Jason Szumlanski

          Fafco Solar



          From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Nick Soleil
          Sent: Wednesday, February 02, 2011 12:05 PM
          To: RE-wrenches
          Subject: Re: [RE-wrenches] Parallel wire runs to increase size



          You shouldn't parallel wiring that way.  That is not acceptable by code, and it is unnecessary.   If the #10 is not sufficient just replace it.  Due to the fact that the larger wiring has much less resistance, most if not all of the current will flow on the larger wires.



          Nick Soleil
          Project Manager
          Advanced Alternative Energy Solutions, LLC
          PO Box 657
          Petaluma, CA 94953
          Cell: 707-321-2937
          Office: 707-789-9537
          Fax: 707-769-9037




----------------------------------------------------------------------

          From: "Starlight Solar, Larry Crutcher" <larry at starlightsolar.com>
          To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
          Sent: Wed, February 2, 2011 8:00:07 AM
          Subject: [RE-wrenches] Parallel wire runs to increase size

          Wrenches,



          Some of our business involves repairing poor PV solar installations on recreational vehicles. So often we wind up installing a roof junction box and running a second PV to controller wire and then replacing the controller to battery wire size. For instance, we may find a 10 gauge wire run to the controller. We then add #8, #6, #4 or even 2 gauge and parallel to the #10 depending on power and distance of the run. My question: Is there a calculator or chart that will tell me what the combination of any two wire sizes equate to? example: #10 + #4 = X

          Thanks.
          Larry Crutcher
          Starlight Solar Power Systems
          powered by STARLIGHT™

       


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