NEC or not, 1000 amps per square inch is wildly conservative.
It really depends on how much voltage drop you can stand and what
temperature rise of the conductor you are willing to accept.
I have a spreadsheet I use to determine PCB circuit trace widths for
high current traces on PCBs I design.
That shows if I have 2 oz. copper (~3mils thick) I can get 30 amps with
only a 20C rise with a 0.5" wide trace. Your suggested bus bar is 20
times as thick and is exposed on each side. Based on that your bus bar
could theoretically handle 600 amps without significant temperature
rise. Of course, one can't really scale it like that as the surface
area to dissipate the heat is much smaller per amp so it would not be
anywhere near 600 amps. However, it would be substantially more than
the PCB trace. If I force it to model your bus bar (which puts it out
of where the results are totally correct) it gives me an answer of 250
amps for the size of your bus bar at 20C rise. While this is probably
wrong, it is not far wrong and your bus bar is exposed on both sides
which a trace is not.
If you are concerned about voltage drop, again my program calculates
that as well. With the above mentioned trace, the resistance of a 12"
long section would be .0066 ohms and the voltage drop would be 0.2 volts
if the 30 amps traversed the whole length. Since your bus bar is 20
times as thick, the resistance is 20 times less and the voltage drop is
20 times less (0.01V per 12").
Also consider that NEC requires that house wiring fused at 30 amps only
need be 10 ga.
If it makes you feel better to double it up, then you should do it, but
it is really unnecessary.
Dick Tasker
RB Lists - Electrical Systems wrote:
>
> OK All...
>
> Being an electrical instructor I have nothing else to do all day than
> to dwell in the minutia of electrical conductivity and what not. So,
> here is my latest musings:
>
> According to the National Electrical Code a chunk of copper bus is
> good for 1,000 amps per square inch. Cutting that down to 1" x 0.5"
> makes it 500 amps. Cut it down even further into 16 pieces (0.5" x
> 0.0625") gives me 31.x amps.
>
> I was going to use the little pieces of copper that I acquired to
> connect my alternator to my shunt and make the other connections to
> the relays and what not.
>
> Now that I have shed some light on this I am wondering if I need more
> conductor than that. Now I know that there will me only moments of
> coincidental loading and 30 amps is pretty healthy and that figure is
> pretty conservative but I cant help but wonder what others have done.
>
> I am also interested in how your solution is lasting over time and if
> you would do anything different.
>
> What does Van suggest on his electric plans? I don't have a copy. I
> know that 'lectric Bob shows a #2, a #6 or #8 in these locations.
>
> Thoughts?
>
> I am considering doubling up the 0.0625 stuff that I already have.
>
> Confused
>
> CJ
>
>
> ------------------------------------------------------------------------
>
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>
>
> rivetbangers.com - Discussion topic
>
http://www.rivetbangers.com/forums/view ... 6117#36117
>
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CJ
CJ