568 



ELECTRICAL EQUIPMENT 



temperature rise in excess of this value and the bus-bars not in 

 excess of 35 C. above the ambient temperature. 



The curves in Fig. 358, which have been derived from a large 

 number of actual tests, show how the current density in amperes 

 per square inch, based on a 30 C. rise, will vary in accordance with 

 the number and width of lamination. The bars are J inch thick 

 and run on edge, and the spacing between the laminations is also 

 J inch and between the centers of the phases 8 inches. 



The great variations in the density for the different conditions 



Number of Laminations 

 1 2 3 4' 5 6 



Alternating Current 

 60 Cycles 



FIG. 358. Permissible Amperes per Square Inch in Copper Connections. 



Installed in Open Air on Edge, 

 j" Spacing between Laminations. 

 Laminations j" thick. 



8" Spacing between phases. 

 30 C. Temperature Rise. 



is apparent from the curves. An increase in the spacing between 

 laminations from J inch to J inch will naturally increase the ven- 

 tilation, and thereby the permissible current which can be carried 

 at 30 C. rise, at least on direct-current. For several lamina- 

 tions, run flat, that is, with their width parallel to the floor, the 

 heating will be at least 25 per cent greater than when the bars 

 are run on edge. Furthermore, consideration must be given to 

 the fact that the ventilation of buses in compartments is not as 

 good as in the open, and for this reason it will generally be advis- 

 able to limit the temperature rise for such conditions to a figure 



