APPENDIX 



THE REACTANCE OF STRANDED CONDUCTORS 



THE reactance of a stranded conductor is appreciably 

 different from that of a solid wire. For example, the 

 reactance of No. oooo cable of seven wires at 60 cycles 

 and 1 8-inch spacing is 0.552 ohm per mile, while the re- 

 actance of a solid wire of the same sectional area is 

 0.560 ohm, and of a solid wire of the same diameter as 

 the cable, 0.544 ohm. Thus the error in using a solid 

 wire formula is in either case 1.5 per cent, which is too 

 large to be neglected. This was explained by the author 

 in " Transmission Line Formulas," Chapter XI, and 

 formulas were given for 7-wire strands and ig-wire 

 strands, which are the most common types of transmis- 

 sion-line conductors. The author has later published a 

 more complete derivation of these formulas, with exten- 

 sions applying to other types of conductors, in The Elec- 

 trical World, April 19, 1913. The calculations in that 

 article are here presented because the formulas are use- 

 ful, not only in preparing tables of line constants, but 

 in calculating the characteristics of transmission lines 

 whose conductors have either an unusual size or number 

 of wires. 



The reactive voltage drop in an alternating-current 

 circuit is due to alternating magnetic flux surrounding 

 the conductors. Since flux which cuts both conductors 

 does not produce a difference in voltage between them, 

 and, therefore, does not produce any reactive drop in 



109 



