Suitable array to controller cable?

alyazalyaz Solar Expert Posts: 114 ✭✭✭
Is this a suitable cable for array to controller? It is listed as a direct bury cable. (Do I need to edit the link somehow to delete the seller and pricing?) Thanks.


http://www.wesbellwireandcable.com/Romex/UFB6-2.html
3.3 kW solar.  3 Midnite Solar controllers; 5 lightening suppressors.  Magnum’s inverter; auto gen start, BMK.  Davidson 2 v FLA’s - 24v bank.  Perkins diesel gen.

Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,006 admin
    Re: Suitable array to controller cable?

    No, you do not need to edit the link. "Incidental" vendor and pricing information is not a problem.

    Is 10 AWG OK for your needs?

    Personally, I like to bury good sized plastic conduit so I can pull new wire later, or pull larger gauge wire later without having to dig up the old cable.

    Also, I like to put a second conduit too if there is a chance you need to send AC power to an out building or pull some control/monitoring/networking cable.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • alyazalyaz Solar Expert Posts: 114 ✭✭✭
    Re: Suitable array to controller cable?

    So this is 10 ga. and not 6 ga? Hmmmm.... Guess I'd better confirm what this really is...
    3.3 kW solar.  3 Midnite Solar controllers; 5 lightening suppressors.  Magnum’s inverter; auto gen start, BMK.  Davidson 2 v FLA’s - 24v bank.  Perkins diesel gen.
  • BB.BB. Super Moderators, Administrators Posts: 32,006 admin
    Re: Suitable array to controller cable?

    Opps... My mistake... 2x 6awg plus 1x 10awg ground.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • firerescue712firerescue712 Solar Expert Posts: 95 ✭✭
    Re: Suitable array to controller cable?

    Isn't it better to run DC through stranded wire? The wire actually flows along the outside of the wire. Right? Just wondering. Thanks, forum gurus.
  • alyazalyaz Solar Expert Posts: 114 ✭✭✭
    Re: Suitable array to controller cable?

    In checking further with the supplier and closer at the website/description I learned that the picture is a generic picture used for all the different gauges and that the copper wire is in fact stranded. The narrative says the following:

    *Each conductor has 7 Strands of bare copper

    Part Number - UF-B 6/2
    Awg and # of Conductors - 6/2
    Stranding - 7
    Ground Wire Size - 10
    3.3 kW solar.  3 Midnite Solar controllers; 5 lightening suppressors.  Magnum’s inverter; auto gen start, BMK.  Davidson 2 v FLA’s - 24v bank.  Perkins diesel gen.
  • BB.BB. Super Moderators, Administrators Posts: 32,006 admin
    Re: Suitable array to controller cable?

    More or less, "skin effect" and "skin depth" are associated with AC current...
    Skin effect is the tendency of an alternating electric current (AC) to distribute itself within a conductor with the current density being largest near the surface of the conductor, decreasing at greater depths. In other words, the electric current flows mainly at the "skin" of the conductor, at an average depth called the skin depth. The skin effect causes the effective resistance of the conductor to increase at higher frequencies where the skin depth is smaller, thus reducing the effective cross-section of the conductor. The skin effect is due to opposing eddy currents induced by the changing magnetic field resulting from the alternating current. At 60 Hz in copper, the skin depth is about 8.5 mm. At high frequencies the skin depth may be much smaller. Increased AC resistance due to the skin effect can be mitigated by using specially woven litz wire. Because the interior of a large conductor carries so little of the current, tubular conductors such as pipe can be used to save weight and cost.

    For solar PV sized systems, you really do not need to worry about skin depth until you hit around 4/0 wire (big stuff). 0.46" / 11.684mm 125 Hz (120 Hz ripple current for 60 Hz inverters).

    Otherwise, stranding makes for cable that is easier to bend and withstands flexing better...

    For example Welding Cable has many very fine strands--which is great for flexing and things that move/pivot/subject to vibration... However, because there is a lot of "air" in the cable because of the fine wire--it is actually quite difficult to find crimp connects that will work correctly and not pull out after crimping.

    And if you use solder to make up a connection--the solder acts like a pivot point which focuses the bending--making the wire easier to work harden and break.

    Also, if you are using the typical screw type clamps for connecting up your breakers/controllers/etc... The very fine "welding cable" does not make a very good connection.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • firerescue712firerescue712 Solar Expert Posts: 95 ✭✭
    Re: Suitable array to controller cable?

    So it is better to use single strand wire? I am going to replace the 2 ga with 4/0 on my batteries in anticipation of future upgrades. I was going to use welding wire. What is recommended? I was also going to use the screw type clamps, instead of crimps. Again, what is recommended? I would hate to rearrange once the system is complete and have to cut off crimp connectors on excessive wire.
  • BB.BB. Super Moderators, Administrators Posts: 32,006 admin
    Re: Suitable array to controller cable?

    Check with your local battery distributor or welding shop and see what they recommend.

    Our host NAWS (Northern Arizona Wind and Sun) has 4/0 "welding style" cables and they also sell various crimp connections and a hammer crimping tool.
    Note: We are currently transitioning from using welding cable to using MTW UL listed cable for all our battery/inverter wiring. Many solar companies sell welding cable for use with batteries and inverters. There's no safety issue when using welding cable, but it can cause problems with some electrical inspectors. Technically, welding cable is only meant to be used on welding machines. When welding cable is used on anything but welders, it violates the national electric code (NEC). This is why we've started using MTW listed cables. MTW stands for "Machine Tool Wire" and it's essentially the same thing as welding cable, but with a more versatile electrical listing. This means it's approved for many more uses than standard welding cable. If you would like to learn more about cable and wire listing and use, please read this article entitled "Clarifying Confusing Cables" from Home Power Magazine. Currently, only the 5 and 10 foot inverter cable pairs are MTW listed. All other cables are welding cable, unless otherwise specified.

    Also, I may be a bit overboard on the warning of high flex (small strands) cables and crimp connections--That was my experience years ago trying to make large computer power supply connections that would meet NEC, UL, and Telephone Company requirements. Was not easy to find a UL LISTED configuration.

    Obviously, UL and such are not usually a requirement for off-grid solar... You can always try and make up a connection and give it a really good yank to see if it fails or not (the cable should fail before the crimp if done correctly).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • firerescue712firerescue712 Solar Expert Posts: 95 ✭✭
    Re: Suitable array to controller cable?

    Thank you, Bill. Since this is a new install, I want to place the proper equipment and materials in place the first time. I will look at the Machine wire.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Suitable array to controller cable?
    Isn't it better to run DC through stranded wire? The wire actually flows along the outside of the wire. Right? Just wondering. Thanks, forum gurus.
    You are thinking of skin effect, which is only for AC and more pronounced at high frequencies. For DC it is not a factor. However, stranded wire is much easier to handle, so that is what I would use.
  • bmetbmet Solar Expert Posts: 630 ✭✭
    Re: Suitable array to controller cable?

    If MTW wire is essentially the same as welding wire, does the "MTW" make it more expensive?
  • firerescue712firerescue712 Solar Expert Posts: 95 ✭✭
    Re: Suitable array to controller cable?

    If the skin effect is for AC, why do we use solid strand wires in AC services? It appears since stranded wire works for automotive situations, it would be even better for residential. Is the issue the insulating material? Or that it would require different connectors for receptacles and switches? Just wondering.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Suitable array to controller cable?
    If the skin effect is for AC, why do we use solid strand wires in AC services? It appears since stranded wire works for automotive situations, it would be even better for residential. Is the issue the insulating material? Or that it would require different connectors for receptacles and switches? Just wondering.

    The wire gauges used for most AC applications are small enough that there is essentially no skin effect. For house wiring, solid wire is cheaper per foot and easier to install. For automotive wiring, the need for flexibility and a lot of bends makes stranded wire a better choice.

    An example of extreme skin-effect handling would be the flat, braided stuff used for grounding lightning rods (lightning being very high frequency).
  • firerescue712firerescue712 Solar Expert Posts: 95 ✭✭
    Re: Suitable array to controller cable?

    Coot, with that said, which is the best for battery bank wiring? Stranded or solid? I know size matters, too. I will replace the 2 ga with 4/0. Then I will not have to replace the wiring as the system upgrades. Also, what type of wire? Welding? Machine wire? Romex-like (term used to prevent trademark use). LOL! If you were to wire a new battery bank, which wire would you use?
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Suitable array to controller cable?
    Coot, with that said, which is the best for battery bank wiring? Stranded or solid? I know size matters, too. I will replace the 2 ga with 4/0. Then I will not have to replace the wiring as the system upgrades. Also, what type of wire? Welding? Machine wire? Romex-like (term used to prevent trademark use). LOL! If you were to wire a new battery bank, which wire would you use?

    4/0 solid is not wire, it is a bar. ;^)

    But seriously, stranded. I don't think you'll find 4/0 solid anywhere, anyway.
  • firerescue712firerescue712 Solar Expert Posts: 95 ✭✭
    Re: Suitable array to controller cable?

    True, it would be an EXPENSIVE bar! What type of stranded? the type used in ac voltage (large strands)? The type used in automotive (Smaller strands)? Or the type in welding wire (Very small strands)? I am watching for bargains, so share your knowledge so I can make an educated decision. I trust the information all share on here. I will use this to buy the wire...soon. Thank you.
  • BB.BB. Super Moderators, Administrators Posts: 32,006 admin
    Re: Suitable array to controller cable?

    OK... See if I can answer the the questions compently (I am sure others here can "help me" :roll:):

    Using "MTW" rated wire should carry a UL/NRTL "LISTING" with reference to NEC and approved applications/uses.

    The whole LISTING/REGISTRATION/UL Traceabliity/Build Inspector chain uses "each piece" of the regulatory/manufacturing chain to allow for the end product/installation to be "safe" is used as directed. And there are independent NRTLs (nationally recognized testing laboratories) that (in theory) monitor the entire manufacturing chain to ensure that Recognized/Listed product is manufactured per the original requirements (traceability of insulation back to plastics manufacture, etc.).

    Not to say that welding cable insulation is "bad"--Just that it is not specified to a standards framework (temperature, oil, sun, abrasion resistance, etc.)...

    Should MTW cost a whole lot more--Not really. The cost (for the most part) appears to be in the copper wire.

    There is "high flex" cable for specialized applications (such as diesel/electric Railroad Engines and their constant vibration)... But, at the time it was not UL Listed (when I needed high flex cable).

    Of course, it depends on the supply chain (miles of welding cable vs ???? of MTW).

    Regarding Solid Wire... It creates a more stable electrical connection when used with typical screw and jaw type clamps for typical home wiring devices (I am guessing). Probably a little bit cheaper to use one solid wire than to make up bundles of stranded cable.

    In larger gauge cabling--From what I have seen (not an electrician), stranded is used because it is simply easier to work with (bend around corners). However, the strand count is still very small (6 awg = 19 strand; typical?). A quick Google did not return any 6awg solid THHN wire (as an example).

    For 60 Hz wiring, skin depth does not really become an issue until you hit ~4/0 (0.46") diameter cable (125 Hz)--Which is good to ~200 amps or so... About the limit for the typical home panel.

    However, it does come close to being an issue with DC input to large AC inverters (4/0 cable, ~200 amps, 120 Hz of ripple current to create the 60 Hz full wave output--each 1/2 of the 60 Hz sine wave peak draws a current pea from the battery bank--little energy storage in an inverter--current levels are too high, and it would probably add a fair amount to mfg costs too).

    At least in my industry (computer systems), if we need low impedance ("aka" resistance including the effects of capacitance and inductance), we use "flat" cables and bus bars. I would assume that large building power systems would make use of flat bus bars to account for skin effects. I have seen slices of "bus bars" used in substations, and they are "just" copper tubing (again recognizing where to put the copper for cost effective current transfer).

    Don't worry if this does not make sense... The math behind DC power (for the most part) is pretty easy--Only needed an Edison to understand. The math behind AC required somebody like a Tesla to understand and implement in the "real world".

    Edison vs Tesla: The War of Currents
    War of Currents - Wikipedia

    Not to say that AC "won the war"... Even today, very long / high powered transmission lines are sometimes done with DC--Even with the add expense of AC/DC/AC conversions, it can still be cheaper and solve several major technical issues (decouples the "60 Hz" AC synchronization issues between power grids a 1,000 miles apart).

    High-voltage direct current - Wikipedia

    Hope this helps answer your questions (or at least creates more questions ;)).

    -Bill "the more I learn, the less I realize I know" B. :cry:
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • firerescue712firerescue712 Solar Expert Posts: 95 ✭✭
    Re: Suitable array to controller cable?

    That was a lot of info. But I am still at a loss as to which thickness of strand is better within the 4/0 cable. I know the thicker the strand, the more rigid the wire. Or do the number or strands really matter for DC amperage?
  • BB.BB. Super Moderators, Administrators Posts: 32,006 admin
    Re: Suitable array to controller cable?

    For "typical" DC systems of less than 200 amps (going to an inverter), 4/0 cabling does not matter whether it is stranded or not in terms of electrical connectivity.

    The only issue between "coarsely and finely" stranded cable is flexibility and how you make the physical connections.

    NEC/UL/etc. typically do their connection testing/ratings with solid (smaller gauge cable) and coarsely stranded cables.

    If you need finely stranded cable for flexibility (easier to route around corners), then you need to find the proper method(s) to terminate them.

    The terminal ends sold by NAWS, when used with some sort of crimping tool (hammer, hydraulic, or even folks that have made their own out of cable cutters--heat to draw temper, drill several different diameter holes in "blades", re-temper, crimp with new hole) should work fine--But you probably will need a larger "raw fitting" diameter to fit finely stranded cables and crimp down farther for a proper connection.

    Sorry--I am not in that industry--So I would recommend calling NAWS or your local battery supplier and see what they can help you with. I don't want to lead you down the wrong trail and your spouse or kids ends up having to call you "at work". :blush::cry:

    I have soldered more than my fair share of cables (at home when I was a kid)--so I cannot hold myself as following my own recommendation of crimp over solder.

    But, if you solder, make sure the cable is well supported and that there is no ongoing bending/flexing at the solder joint (work hardens the copper at the solder interface). Also, you want the cable supported so that if the solder joint melts (over current/fire) that the cable does not pull-out / separate and cause more problems (short circuits else where).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • firerescue712firerescue712 Solar Expert Posts: 95 ✭✭
    Re: Suitable array to controller cable?

    Very good information. Again, thank you. I have mad more than my share of bad decisions in this solar set up. I am trying to prevent any more. I appreciate your time to put this in writing.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Suitable array to controller cable?

    When I worked for Emerson we had a book of "available wire types". After five minutes reading that your brain would melt and run out your ears. :p About 80% of the differences were in the insulation, btw.

    There's a couple of aspects with sold vs. stranded vs. fine-stranded. One is the skin effect with AC/high frequency which doesn't have much bearing on DC. DC pretty much just wants it to be big enough to handle the current. The other is the flexibility of the wire; more strands = more flexible. This is not a major concern in fixed installs like house wiring where nothing is supposed to move anyway. Welding cable is fine-stranded because it gets moved around a lot while you're welding. Usually the insulation on this is also highly flexible (until it gets old) but not UV resistant. Heck they make stuff with silicone jacketing!

    Then there's the matter of transitioning from wire to connector. As Bill noted the solid stuff works fine with screw terminals or those dreadful push-in connectors on outlets and switches (which in my opinion ought to be banned). Stranded needs to be crimped/soldered into a lug connector. Wrap stranded wire around a screw and you get loose strands trying to jump out and cause shorts. To say nothing of the heat cycling loosening the screws (hard to get proper torque against 'soft' strands).

    For battery wiring I use regular stranded. Easy to attach/remove. I've used solid bar interconnects, but they can be a pain if the batteries or holes aren't in just the right place. Never used welding cable, but it would work. Bit of a pain getting a good crimp on all the little strands.
  • firerescue712firerescue712 Solar Expert Posts: 95 ✭✭
    Re: Suitable array to controller cable?

    I knew you would jump in soon, Cariboucoot. Thank you both for the information. I hate crimps, but it appears they are the best choice for connectors. It seems there is really no difference in the stranded wires as far as DC current goes. I'll shop around for the best stranded 4/0 prices.
  • brandywinebrandywine Registered Users Posts: 15
    Re: Suitable array to controller cable?

    We have a 12v system (for now) and here is what we did to make our cables.
    cabletools.jpg
    We borrowed this crimper from our local NAPA store.
    cablelugs.jpg
    1-0weldingcable.jpg
    1/0 Welding cable
    crimping.jpg
    Whack!
    completecables.jpg
    Top cable was our first try=CRAP. Lead deformed and kept getting loose.
    Bottom cable is the completed one.
    crimp is solid and secure if you use a sledge about 24" drop.
    Working great!

    ---
    Mickie & Travis
  • firerescue712firerescue712 Solar Expert Posts: 95 ✭✭
    Re: Suitable array to controller cable?

    Thank you so much. THAT is what i was wondering about. I work on the KISS principle. Keep It Simple Stupid. I have the first wire type in your pics. I agree, they are not very secure. Guess it is time to get the sledge hammer out.
  • brandywinebrandywine Registered Users Posts: 15
    Re: Suitable array to controller cable?

    Here is that welding wire connected to the back of our Xantrex inverter.
    inverterconnect.jpg

    -Mickie & Travis
  • hillbillyhillbilly Solar Expert Posts: 334 ✭✭
    Welding cable and crimping

    I've just done a whole bunch of work with 2/0 and 4/0 welding cable (from NAWS), using a hammer crimper to crimp the lugs on. As Bill has pointed out it IS tough to get a really good crimp; although I had ordered a couple of extra lugs just in case, I had to re-order a few more because I had 4 pull out. Be sure to test pull on those lug ends a few hours or even better a day or two later and see just how tight things really are.

    Thing is, I overall still prefer using welding type cable for battery/inverter wiring. I've used 3/0 stranded wire in the past and it can be very difficult to use in certain instances. The issues that I found were: tough to get very precise placement with any major curves in the routing of the wire, and hard to use really short lengths unless the runs were very straight. The thicker the wire gauge the more of an issue this becomes, so for me I like how flexible the 4/0 welding cable is, but as noted it can be difficult to get a really solid crimp on it. It could also be argued that it's hard to get a solid and safe connection when your heavy cable is too stubborn to bend the right amount for the terminal end...

    Either way, this piece of the system really is kind of like the footings in a foundation; easy to overlook or rush through while more concerned with the "big stuff" ahead, but critical to the health and safety of the whole system.

    P.S. on using those hammer crimpers, maybe it was just me but I found that you really, really need to stabilize and support the terminal lug AND the crimper itself when you're pounding on it. Maybe it was because I was using a framing hammer rather than a big heavy sledge as suggested above? What I found was that often the terminal lug would tend to crimp at an uneven angle as the wires would try to squeeze out as I was hammering away. I made it work by pushing hard on the cable end while the terminal lug was butted up against a braced 2x4. Pre taping the lug to the cable also helped to keep things tight and straight for at least the first few good whacks, which is where the wire is most prone to sneak out.
  • brandywinebrandywine Registered Users Posts: 15
    Re: Suitable array to controller cable?

    *none* of our first tries with a hammer worked. Those lugs are pricey so we brought out the big boy....!
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Suitable array to controller cable?

    Could you use a vise instead of a hammer?
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