Re: [RE-wrenches] Battery Bank to Inverter Wiring

[Allan Sindelar]

As a matter of course I have always run the positive and negative conductors of high-current cable pairs together, but have never deliberately twisted them, and have never known of any related problems. The most obvious example of this would be 4/0 battery/inverter cables in a 24V system, with a 250A GJ-class breaker or (prior to that) a 300A or 400A Class T fuse. It's pretty tough to thread a twisted pair of 4/0 USE/RHH/RHW cables through a 2" elbow or LB from inverter enclosure to battery enclosure. I'm not an EE, but I can't see what difference twisting would make in the absence of a building/collapsing field as is normal with AC. I have twisted AC conductors together in the past when clients have expressed concerns about EMF from their equipment and wiring, but only AC. Allan Allan Sindelar al...@sindelarsolar.com NABCEP Certified PV Installation Professional NABCEP Certified Technical Sales Professional New Mexico EE98J Journeyman Electrician Founder (Retired), Positive Energy, Inc. 505 780-2738 cell   On 6/27/2015 2:40 AM, John wrote: That is why for years we have been twisting those leads around each other.  I was told it was to cancel out the opposing fields on the wires, but for whatever the correct technical reason is,  we have always twisted those heavy wires.         John V.   From: RE-wrenches [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of jarmo.venalai...@schneider-electric.com Sent: Saturday, 27 June 2015 5:45 a.m. To: RE-wrenches Subject: [RE-wrenches] Battery Bank to Inverter Wiring   Hi: From time to time over the years I've come across systems where the routing of DC cables between the batteries and the inverter has been the cause of  issues. I'm not referring to wire thickness or quality of terminations.  For the purposes of this discussion, just assume that wire thickness and terminations are perfect. What I am referring to is the routing of the positive and negative battery cables.  In particular, the loop area within the + and - cables as shown in the image below, The problem I've seen in systems with a large loop in the setup is that the inverter does not provide good surge power and can even go into low voltage shutdown during large surges. Recently this happened again and I wanted to get a better feel for it, so I did some math.   For a cable length of about 12', the loop is an inductor which has a value of inductance of about 1 uH for side by side cables and as much as 6 uH for cables about 1 foot apart.   This inductance is greatly multiplied by any ferrous metal in the loop and can easily be in the range of 10's to 100's of uH.  Examples being cables which run in steel conduits or along the steel frame of a motor home. Inductance causes a voltage drop proportional to the rate at which the current is changing.  To get an idea of how large that rate can be for typical inverters, I did surge tests with a 5kW inverter and found that the rate of change of current can be as high as 100A per milli-second or 100,000 Amps/second. Given that, the voltage drop of the wire inductance is then , Vdrop = (rate of change of current) x (inductance), Vdrop for 1 uH = (100,000 A/s) x (0.000001 H) = 0.1V Vdrop for 10 uH = (100,000 A/s) x (0.000001 H) = 1.0V Vdrop for 100 uH = (100,000 A/s) x (0.000001 H) = 10.0V    clearly this is a problem. Have any of the wrenches had systems with this issue?  If so, how often. JARMO   _____________________________________________________________________________________ Jarmo Venalainen  |   Schneider Electric   |  Xantrex Brand  |   CANADA  |   Sales Application Engineer Phone: +604-422-2528  |   Tech Support: 800-670-0707  |   Mobile: +604-505-0291 Email: jarmo.venalai...@schneider-electric.com  |   Site: www.Xantrex.com  |   Address: 3700 Gilmore Way, Burnaby, BC V5G4M1 *** Please consider the environment before printing this e-mail _______________________________________________ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org

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