Slots/holes on bus bars, what's the effect?
Slots/holes on bus bars, what's the effect?
(OP)
Some copper busbars being used on switchgears are pre-fabricated with slots/holes for ease of installation and interconnection. Example is a 1/4" x 4" square busbar with 3-slots in a row/column. The size of the slots is about 1/2" x 1" (oval shaped). Obviously, these slots reduce the cross section of the bus bar from 1sq.in. to 0.625sq.in. on that particular portion. But, what or how much is the effect on the ampacity of the bus bar as a whole? A more specific example is a 4-ply 1/4" x 4" horizontal copper busbars having slots indicated before, will it still be rated for 4000 amperes? Switchgear manufacturer said yes. But I'm not convinced since no technical information or data was provided. Any thoughts?






RE: Slots/holes on bus bars, what's the effect?
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RE: Slots/holes on bus bars, what's the effect?
RE: Slots/holes on bus bars, what's the effect?
RE: Slots/holes on bus bars, what's the effect?
From another switchgear manufacturer that I consulted, the normal practice is after the busbars are fitted, the slots that will not be used will be filled before plating the entire length of the bar.
From a table at copper.org, a 4-ply 1/4" x 4" will have an ampacity of 4328amps on a 30degC rise and 40degC ambient. This is for a whole bus bars w/o the slots being mentioned here.
RE: Slots/holes on bus bars, what's the effect?
Look up the rating for the reduced cross section. I believe 4" minus 3x 1/2" slots would be equivalent of 2.5" wide bus bar from a standpoint of cross section at that point only (if I have understood the geometry correctly).
The actual ampacity would be somewhere between the 4" and 2.5" busbar (both quarter inch), and I believe much closer to the 4" due to the high thermal conductivity of copper as mentioned above.
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RE: Slots/holes on bus bars, what's the effect?
Table 13.2 rates 4000A as (4)1/4 x 5 cu bars or (5) 1/4 x 4 cu bars.
These are UL's guidlines. Other bar sizes and the amount of material removed may be different if the heat rise tests are performed on the specific construction.
RE: Slots/holes on bus bars, what's the effect?
RE: Slots/holes on bus bars, what's the effect?
Sarg