[RE-wrenches] Parallel wire runs to increase size

[Exeltech]

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 SzumlanskiFafco 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 sizeWrenches, 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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