Bussco Bus Bar Physical Design Characteristics

Cross Sectional Area Considerations and Determination

The required cross sectional area of a copper conductor for a given amperage requirement and a temperature rise of 30° C max from ambient can be determined by the following formula:

Formula (2.7)
A = 300 x l x [1 + .075 (N - 1)] Sq. Mils

Where,
l = curent in amperes
N = number of conductors

For multiple layer bus bars, the cross sectional area calculated for each conductor should be increased by approximately 7½% to account for the decrease in heat dissipation between conductors. This is already accounted for in formula (2.7) above.

Conductor Thickness and Width Calculations

The width calculation for a given cross sectional area can be determined by selecting an appropriate standard thickness and using the following formula:

Formula (2.8)
w = A / (1 x 10⁶ ) / t conductor width in inches

Where,
A = cross sectional area as calculated from formula (2.7)
t = conductor thickness in inches selected from the list below

Available Standard Alloy 110 Thickness copper conductor:
0.020", 0.032", 0.040", 0.062", 0.093", 0.125", 0.187", 0.250", 0.375", 0.500", 0.750"

For a given cross sectional area and taking into consideration the space and structural application requirements, the combination of a very thin and wide conductor, or having a maximum w/t ratio, has the following benefits:
• Inductance is minimized; formula (2.5)
• Capacitance is maximized; formula (2.4)
• Low characteristic impedance

The ampacity table gives the width, per formula (2.8) for a given current, a given conductor thickness and a temperature rise of 30° C max from ambient. A series of widths is calculated for the same current using all the available standard widths. The corresponding resistivity and inductance / length are calculated for each thickness and calculated width.