Effects of Emissivity and Number of Copper Busses on Ampacity

Data here show how higher emissivities improve ampacity. Multiple busses also affect ampacity in a nonlinear relationship. Ampacity may be raised by increasing heat dissipation through the use of convection cooling or surface treatments.

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Number of 1/4 x 4 in. Busses*	Ampacity, Amp
	30 °C Rise				50 °C Rise				65 °C Rise
	Emissivity				Emissivity				Emissivity
	0.15	0.4	0.7	0.9	0.15	0.4	0.7	0.9	0.15	0.4	0.7	0.9
1	1100	1250	1400	1600	1500	1700	1900	2000	1700	1950	2200	2300
2	1900	2050	2200	2300	2550	2750	2950	3100	2950	3200	3400	3600
3	2500	2700	2850	3000	3400	3600	3850	4000	3950	4200	4500	4600
4	3100	3300	3450	3600	4200	4400	4700	4800	4900	5100	5400	5600

*1/4 in. spacing. Ampacities of bus bar systems of other configurations must be calculated, taking into account size, spacing, number of bus bars and overall skin-effect ratio.

Table courtesy of Copper Development Association Inc. (www.copper.org)