CHARACTERISTICS OF TOLL TELEPHONE CABLES 



299 



The normal variation of air temperatures in the middle western part 

 of the country is from about 1° Fahrenheit, (—17° Centigrade) to plus 109° 

 Fahrenheit (43° Centigrade). Extremely hot summers like that in 1936, 

 which was preceded by a severe winter, show even higher temperatures and 

 there are occasional periods in mid-western winters when the temperature 

 hovers continuously around —30° F., for a week or two. These tempera- 

 tures are almost the temperatures assumed by open wires, but wires inside 

 a lead sheath like those in an aerial cable are subjected to much higher than 

 air temperatures in hot weather when exposed to direct sunlight in the 

 absence of wind. Some observations made at Lagrange, Indiana, in 1936 



10 2.0 30 40 50 6 70 80 90 100 110 120 



TEMP. - DEGREES FAHR. 



A/? 



Fig. 3 — Resistance-temperature coefficienl 5- in ohms per ohm per 1° 



A! 



fahr.-19 gauge cable 



on d-c. resistance of cable pairs showed that temperatures in the ten miles 

 of cable averaged about 122° Fahrenheit (50° Centigrade) when the air 

 temperature read on thermometers was about 104° Fahrenheit (40° Centi- 

 grade). Similar data taken at Chester, New Jersey, showed temperatures 

 in the cables 20° to 25° Fahrenheit higher than the air temperature on 

 hot bright days. 



The actual observed cable temperature range in that season (1936) as 

 indicated by the d-c. resistance measurements was thus from —4° Fahren- 

 heit (—20° Centigrade) to 122° Fahrenheit (50° Centigrade). In terms of 

 a-c. resistance changes, this amounts to a resistance change of about 20 



