By Dan Kitts
On average, 17,000 copper connectors, aka busbars, ship from Storm Copper’s loading dock every day. Thousands of unique designs are included in those 17,000 pieces of copper busbar. Needless to say, we have seen countless prints from many different industries. When our process engineers look at a print, there are a handful of key design elements they are immediately drawn to. These design elements largely dictate how these busbars will be manufactured. It also determines the price we must charge our customer. When considering the design of a busbar, several critical points can favorably impact the cost of fabrication.
Although it may sound obvious, the number one factor in keeping busbar pricing low is often overlooked. Specify only the exact size of copper stock you really need for the job. Whether you are using copper or aluminum for your busbar application, reducing the metal content is your number one opportunity to reduce cost. You will find these ampacity tables very helpful with sizing busbar. To do this properly, you must know the amount of temperature rise you are willing to accept.
One word of caution while we are on this subject; your desire for thickness optimization should not conclude in a special mill run sizes of busbar. Unless you are a very large user of busbar, utilizing readily available busbar thicknesses (these are .062, .094, .125, .250, .312, .375 and .500 inches) permits your fabricator multiple sources of supply and reduced lead times. As of the writing of this article, lead times from the two domestic copper mills in the United States are approximately 8 weeks. Most OEMs we do business with require a lead time of 2 weeks or less on their busbar requirements.
From a fabrication standpoint, punching holes in copper busbar is much more cost effective than milling holes. On busbar less than .500” thick, there generally are two design parameters which force busbar to be routed to the mill. The first is a hole location so close to a formed or bent area of the busbar that the hole becomes deformed. You see, busbar is always punched when it is flat. The only way we can get a hole into a bent busbar is by mounting it on the mill or machining center. This process is slow and therefore expensive. If you can allow a distance of 1.00” or more from a hole location to a bend in the part, we can most often eliminate a stop at the mill.
The next reason a busbar often stops at the mill is tolerance. Once your tolerance gets under +/- .005” on hole placement, we can no long hold these dimensions on our punch presses. Also, the tolerance of the hole diameter is a concern, +/- .001” and we must use a mill to drill the hole. To be sure your part stays off the mill, allow +/- .020” for your tolerance. It is important to note that punching copper busbar does slightly deform the surface of the part.
Occasionally this indenting or rounding of the surface of the busbar can result in a loss of contact area. This minor deformation of the hole is rarely a problem, but worth noting.
To sum up the critical points in reducing busbar cost:
1. Use the smallest possible size to reduce metal content of the busbar.
2. Design in standard thickness busbar to improve availability whenever possible.
3. Review hole placement and tolerance to reduce the chance the busbar would need to be routed to the mill.
Our Busbar Capability Brochure is another source of information that may be of assistance in your design efforts.
If you already have a print of your custom Busbar, simply email it to busbar@stormcopper.com for a fast, reliable quote. If not, good luck on your busbar design efforts, and please feel free to contact us if you have any questions. Our OEM HOTLINE is 1-800-394-4804.
Calling out the gauge of the metal is another way of saying the thickness. It is important to keep in mind that with gauge, the larger the number the thinner the material. 30 gauge copper sheet is much thinner than 16 gauge. To make matters even more confusing, the roofing industry measures copper thickness in ounces per square foot! 16 oz copper sheet is a very common size of roofing copper. Use this cross reference table to help you convert gauge to inches to ounces.