[RE-wrenches] a big bundle of +'s and a separate big bundle of -'s

[Jim MacDonald]

Looking at this older post [below] which came up as I searched "bundling:"

Take this scenario with a blocky array laid out with all the positives on the west and all the negs on the east, CB in the north:
For example, 8 strings of 7:
[1= the positive HR of each string; 7= the negative HR of each string]
As I've drawn below,
On the west array edge, you'd have all the + running north toward the CB in one bundle of only-positive wires,
and the same on the east flank with all the -.

___CB___
+1234567-
+1234567-
+1234567-
+1234567-
+1234567-
+1234567-
+1234567-
+1234567-

Any reason it be better to lay out the array this way, with current flow reversed every other row?:

___CB___
+1234567-
-7654321+
+1234567-
-7654321+
+1234567-
-7654321+
+1234567-
-7654321+

Re: original thread, Is the heating irrespective of whether the bundles are mixed pos/neg, or worse if all 1 polarity?
And, sorry but I could not find what William wrote about the impedance [DC resistance] in this situation.

Hope my question is clear.  Thanks

Jim MacDonald
Design + Engineering Dept.
Solar Energy Systems, LLC
Brooklyn, NY 11222
www.solarEsystems.com<http://www.solaresystems.com/>





From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Phil Undercuffler
Sent: Sunday, July 18, 2010 9:09 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] battery boxes...and conductor bundling

Off hand, I can think of two components to this -- conductor heating, and noise/impedance.  From a conductor heating POV, the NEC is fuzzy on specific distance but the general rule is to not bundle conductors for lengths greater than 18', or standard derates would need to be applied.  With the costs of copper, I think you'd want to avoid unnecessary increasing of cable size wherever possible.

>From a noise and impedance POV, I'd ditto what William Miller says but add twisting the cables if possible, and with the possible additional caveat of conductors of opposite polarity serving the same device.  In most systems the DC negative (usually) conductors are common and therefore this might be moot, but it is theoretically possible to have a system with discrete components and discrete conductors.  (Not sure what that system would look like, but just thinking out loud here...)  In any case, in such a system bundling the positive of one inverter with the negative of another inverter probably won't have the positive impact desired.

Phil Undercuffler


On Sun, Jul 18, 2010 at 11:40 AM, Tom DeBates <habitek83 at yahoo.com<mailto:habitek83 at yahoo.com>> wrote:
hello Wrenches,
  Since we usually are using the batteries in back-up applications and thus AGM batteries, we like to stack them. So we make-up a steel (2"X2" angle) rack, have our tinner bend-up an enclosure, and get all parts powder coated. Expensive, but last forever.
  On another note; what is the skinny on bundling conductors of same polarity?.....Ok, bad?  Searched the archives and the Internets and couldn't find a satisfactory answer.
thanks,
tom

Tom DeBates
Habi-Tek
524 Summit St.
Geneva,IL. 60134
630-262-8193
fax 630-262-1343



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