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  • 1 Post By Maine Sail
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Old 06-25-2013
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Busbar query

Hello,
I was wondering what determines the load capacity (amps) of electrical busbars. Marine stores advertise them in varying sizes and varying load capacities and I assume it is the thickness or width of the bar or the material it is made from that determines what max amps it can carry.

I have several leftover pieces of 6" x 6" x 1/4" flat brass bar in my workshop that I am considering to use in making my own busbars. I intend to make them about 4" long x 3/4" wide x 1/4" thick and I would like to know if there is a way of finding out what the load capacity of these homemade busbars would be.

Thanks,
redx.
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Old 06-25-2013
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Re: Busbar query

you are on the right track, it is the material the bar is made of, the quality of that material, the circular mils of material (size), heat dissipation of the material and the environment that the bar will reside in, ie is it cooled by what process.

Any engineering text book, or electrical code book will have some basics. The pieces you have may be fine for very low amperage uses, but the higher the amperage (heat generated) the more area of bar you will need, you can laminate pieces or parallel them, but that has more math to calculate.

YMMV
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Old 06-25-2013
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Re: Busbar query

Hi YMMV,

Thanks for the reply. I did a bit of googling around on this subject and found a few websites with good information. I guess I should have done that before posting my query here. It seems that conductivity and temperature, as you say, have a lot to do with it. I better do some serious reading before I get too carried away with my bits of brass.

Thanks again,

redx
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Old 06-25-2013
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Re: Busbar query

Most good quality bus bars for marine use will be tin plated copper. Brass is not as good a conductor thus it will need to be bigger to pass the same amount of current..

This article by Blue Sea should help..

Electrical Conductivity of Materials - Blue Sea Systems
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Old 06-26-2013
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Re: Busbar query

Hi Maine Sail,

Thanks for the link to that Blue Sea webpage, here's a quote from it -

"There are instances where the superior tensile and machining characteristics of brass make it a better choice than copper as long as the sectional areas are increased proportionately to achieve the conductivity that a copper part would have in the application."

I'm not sure how I'd go about working out the size increase of the brass to achieve the same conductivity as a copper busbar. It must be acceptable to use brass for this purpose though because it's been used as busbars in household electrical switchboards for years.

redx
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Old 06-26-2013
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Re: Busbar query

Brass is only about 28% as conductive as copper.....about 1/4 the conductivity.

To have the same total conductivity as copper, you'd need a cross-sectional area of brass about four times as large as copper.

In a marine application, I can't think of anything better than tin-plated copper which non-billionaires could afford. So.....I'd use the brass for something else and go with readily available and excellent quality marine bus bars, like those from Blue Sea Systems.

Bill
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Old 06-26-2013
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Re: Busbar query

Thanks Bill,

I'll take your advice and buy a couple of copper busbars.

Cheers,
redx.
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