566 



ELECTRICAL EQUIPMENT 



are run flat or on edge, and whether open or enclosed in compart- 

 ments. For alternating-current work the heating in addition 

 depends on the skin-effect and the 

 inherent reactance of individual 

 laminations and phases. 



The permissible heating will de- 

 pend on the fact whether these bus- 

 bars are simple uninterrupted car- 

 riers of electricity from one end to 

 another, or whether connections 

 are taken off the bus at certain 



FIG. 353. FIG. 354. 



Typical Low-tension High-capacity Switch and Bus Structures. 



points to circuit breakers, etc. In the latter case the heating of 

 the bus-bars or of the whole combination from bus to circuit 

 breaker must be kept at a low enough figure so that the total 

 temperature rise is below the temperature rise permitted for the 

 breaker, which generally is 30 C. The connection bars should, 

 therefore, in such cases be so proportioned as not to develop a 



