And it may look different within a particular switchboard. So, 3000A may look very different from manufacturer to manufacturer. RE: Switchboard asco1 (Electrical) 14 Mar 11 08:46 Or stating a full rated (not tapered) Main Bus with provisions for adding future equipment. I have received specifications requiring that all bus have a current density rating of 800A or 1000A per square inch. So, 3000A may look very different form manufacturer to manufacturer. 25" spacing may be used for a switching device. UL 891 charts specific bar sizes, quantities, and spacings for a particular amperage.Į.g.: 3000A = (3) 1/4 x 6" cu bars with. Less than 3000A = 1000A per square inch.Ĥ. Size and spacing may also be dependent upon the location of the bus within the switchboard. Therefore you might get a greater current carrying capacity with a lower density, large surface area arrangement. Sized and spaced per the manufacturers temperature test results: Most of the current flows along the skin of a bus bar. To a UL 891 Switchboard manufacturer, 100% can mean a few different things.ġ. RE: Switchboard rbulsara (Electrical) 10 Mar 11 19:35 It does not hurt to ask for 100% rated bus. Most importantly specify in plain English what you want, rather leaving it open to interpretation. It is generally is not an issue but there is a difference.Īlso while you are not asking for tapered bus, if you do not specify "Fully" rated (not 100%) Main bus, you may get tapered main bus, that jraef indicated. You have to ask them as to what exactly they mean by that and how do they test it. Most mfrs will take exception to that and provide what is called "heat" rated (I believe that is thermally tested). Many spec calls for certain current density (xxx amps/ sq inch). But their ratings can be determined in different ways. A 3000A switchboard may not be a 100% rated switchboard without using 100% rated breakers, especially the main, even if it has so called a 100% rated bus.īuses are always 100% rated so to speak. When you buy a 3000A equipment, the bus is designed to handle 3000A with no problem for indefinite time (100%).
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