Bar stock Vs Cable

SqueakSqueak Registered Users Posts: 1
Question, 
It's my understanding that electrons flow along the outer edge of the conductor.
If this is true, why would one use a copper bar in [preference to a larger multi-strand cable. The cable will have a significantly higher surface area.

Comments

  • BB.BB. Super Moderators, Administrators Posts: 31,433 admin
    Well... The answer is "it depends" and "it's complicated".

    DC current flows through the entire conductor "evenly". (I am not sure about the "sine squared" waveform at a 120 Hz the is the current flow for typical single phase sine wave inverter--That is a different question)

    RF (radio frequencies) flows on the "skin" of the conductor aka "skin depth".

    Lower frequencies (like 60 Hz line power) flow somewhat deeper in the conductor.

    For example, here is a table of the skin depth vs frequency for various AWG cables;

    https://platt.com/cutsheets/multiple/awg conductors.pdf

    Note that 100% skin depth for 4/0 cable (0.46" in diameter) is 100% at 125 Hz.

    With AC and Radio Frequency currents, there is a lot of math and material sciences involved:

    https://en.wikipedia.org/wiki/Skin_effect

    Large power stations do use hollow copper tubing for their bus bars--Not solid conductors.

    And some applications (such as induction cooktops) use bundles of stranded wire--But the strands are insulated so the current cannot move to the skin of the overall conductor diameter (Litz Wire).

    Where the skin effect and complex impedance (inductance, capacitance, and DC resistance) of wiring becomes more critical for "household" use is with lightning control. Lighting is an "impulse" with frequencies up to around 7,000 Hz or so (low frequency RF)... And you will see heavy braided cable and flat braided cable and flat copper plates used for to help conduct lightning to ground (flat plates have lower impedance vs round wire).

    Does this help? Any more questions?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • JRHillJRHill Registered Users Posts: 29 ✭✭
    I needed a mandatory on the fly kluge when I added shunts to my system -  I needed a bus bar. Pronto. There is no place anywhere close to buy copper stock. I did have some 1" copper tubing. I squashed it flat in the press. With an oxy-ace torch I annealed it. I folded it again and annealed it again. I squashed it tight and drilled the holes. I hard silver soldered the ends and through holes. Polished it up and mounted it with the shunts. I fully intended to order in some copper buss bar but the kludge worked wonderfully. Yeah, a little time consuming but there weren't any other options.
    Two systems: 1) 2925w panels, OB VFX 3648, FM80, FNDC, 240 xformer, three SimpliPHI 3.8; 2) 780w, Morningstar 30a, Grundfos switch, controller and AC/DC pump, 8 T105. Honda EU7000is w/AGS. Champion 3100. Miller Bobcat.
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