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  1. #11
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    Quote Originally Posted by Scott'n'Wendy View Post
    It's because electricity flows on the surface. More surface area...more flow capabilities. More strands = more surface area = more flow = less resistance. Regardless of frequency. Applies to DC as well.
    Sorry, but this is incorrect. What you are describing is called "skin effect" and is directly a function of frequency. At DC (0 Hz), given sufficient distance from a termination, the current flows through entire cross section of the wire. Resistance/current carrying capacity is strictly a function of the TOTAL cross-sectional area (# strands x cross-sectional area of each strand) with DC current. Skin effect usually (for our size wires/strands) does not become an issue until you get into a few 10's of kilo hertz frequencies (10~20kHz). For very large STRAND sizes (say around 1") it is lower, but still in the 100's Hz range.

    Chris

    Chris
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  2. #12
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    Quote Originally Posted by CoChris View Post
    Sorry, but this is incorrect. What you are describing is called "skin effect" and is directly a function of frequency. At DC (0 Hz), given sufficient distance from a termination, the current flows through entire cross section of the wire. Resistance/current carrying capacity is strictly a function of the TOTAL cross-sectional area (# strands x cross-sectional area of each strand) with DC current. Skin effect usually (for our size wires/strands) does not become an issue until you get into a few 10's of kilo hertz frequencies (10~20kHz). For very large STRAND sizes (say around 1") it is lower, but still in the 100's Hz range.

    Chris

    Chris
    Thx Chris….I checked out when he brought up DC flowing on the surface. @chemist308 do an internet search on “skin effect” if u want to read about it. Otherwise it’s about the second level electromagnetics course toward a EE degree. That was many moons ago for me.
    Larry and JoAnna
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  3. #13
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    Well maybe I've not explained my self well. I am not referring to frequency related skin effect. Maybe my understanding of electricity and surface area is incorrect. But why then, is solid or limited strand #8 wire good for 40 amps while extremely fine #8 wire such as DLO, DEL, good for around 80amps? In AC or DC applications.
    Not sure if this is related enough to the op's question to continue. If you know why, Maybe PM me Larry? I'm always willing to learn.
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  4. #14
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    Quote Originally Posted by Scott'n'Wendy View Post
    Well maybe I've not explained my self well. I am not referring to frequency related skin effect. Maybe my understanding of electricity and surface area is incorrect. But why then, is solid or limited strand #8 wire good for 40 amps while extremely fine #8 wire such as DLO, DEL, good for around 80amps? In AC or DC applications.
    Not sure if this is related enough to the op's question to continue. If you know why, Maybe PM me Larry? I'm always willing to learn.
    It’s the application and temp rating.
    NEC table 310-17 is for single conductors in free air, dlo would be an RHH insulation type, 90deg C rating of #8 is 80a.
    NEC table 310-16 is for up to 3 conductors in a raceway. For 90deg C in this application it’s derated to 55a, and at 60deg C it’s derated even further to 40a.
    Larry and JoAnna
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  5. #15
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    Quote Originally Posted by LMagelitz View Post
    It&#8 217;s the application and temp rating.
    NEC table 310-17 is for single conductors in free air, dlo would be an RHH insulation type, 90deg C rating of #8 is 80a.
    NEC table 310-16 is for up to 3 conductors in a raceway. For 90deg C in this application it&#8 217;s derated to 55a, and at 60deg C it&#8 217;s derated even further to 40a.
    Larry, thank you for sighting the corresponding tables and giving such a good explanation. I was just going to **guess** insulation, max allowable temperature and environment (free air, enclosed, etc.)

    Chris
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  6. #16
    Seasoned Camper chemist308's Avatar
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    Wow there's a lot of really good technical info in this thread. I almost feel bad doing it, but I just couldn't sleep right knowing what the owners manual for my charge controllers said. So I got my hands on some 4AWG welding cable which was what I originally wanted to use before the guy at the solar company talked me out of it. This evening we pulled fish tape down to the pass through using the wire lugs on the #8 wire. Then we pulled the welding cable up, lubing it with wire wax--a huge thanks to my Dad for suggesting wire wax. I'd never heard of the stuff. All 4 cables are bolted onto bus bars in the box on the roof.

    Tomorrow I'll cut the cables to length, tin their ends with electrical solder and install them into the cut off breakers and the charge controllers.
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  7. #17
    Site Sponsor FirstAscent's Avatar
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    Quote Originally Posted by chemist308 View Post
    Wow there's a lot of really good technical info in this thread. I almost feel bad doing it, but I just couldn't sleep right knowing what the owners manual for my charge controllers said. So I got my hands on some 4AWG welding cable which was what I originally wanted to use before the guy at the solar company talked me out of it. This evening we pulled fish tape down to the pass through using the wire lugs on the #8 wire. Then we pulled the welding cable up, lubing it with wire wax--a huge thanks to my Dad for suggesting wire wax. I'd never heard of the stuff. All 4 cables are bolted onto bus bars in the box on the roof.

    Tomorrow I'll cut the cables to length, tin their ends with electrical solder and install them into the cut off breakers and the charge controllers.
    In my opinion, using solder to tin the ends is not needed. More important is to make sure you have a good solid cold weld crimp. And that’s coming from someone (me) who went complete overkill on my solar wiring

    Btw- sounds like it’s probably too late but if you do in fact want some truly bomber 8awg PV wire let me know! It’s expensive but the best. It’s 8awg, completely tinned, multi strand (read high strand count), and of course PV rated and UL listed.

    With all that being said and reading your last post, how did everything go if you already finished?

  8. #18
    Left The Driveway
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    To all who claim the "skin effect" applies to DC...I'm open to reconsider what I learned in college physics and electronics if anybody can present more than an opinion. https://www.allaboutcircuits.com/tex...e-skin-effect/
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  9. #19
    Seasoned Camper chemist308's Avatar
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    Quote Originally Posted by FirstAscent View Post
    In my opinion, using solder to tin the ends is not needed. More important is to make sure you have a good solid cold weld crimp. And that’s coming from someone (me) who went complete overkill on my solar wiring

    Btw- sounds like it’s probably too late but if you do in fact want some truly bomber 8awg PV wire let me know! It’s expensive but the best. It’s 8awg, completely tinned, multi strand (read high strand count), and of course PV rated and UL listed.

    With all that being said and reading your last post, how did everything go if you already finished?
    Click image for larger version. 

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    To answer that last question, I’d say it went pretty well. I’m doing this for my battery bank, which is being charged by solar.
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