STANDARDIZATION RULES OF TV/A .4 / R.E. 35 



.uuntuy - y >:-..-:. :n the last column of the above table 

 calt .iture on the centigrade scale at which copper of the par- 



concerned would have aero electrical resist a nr 

 -tweenOdeg. cent and 100 deg. cent, 

 applied .-.ly down to the absolute sero. The usefulneas c: 



erred absolut- :peruture of resistance" in calculating tem- 



perature rise is evident from the following formula: 



*/-*/ 



- ., ' <T 



presentation of the above table is intended to emphasise the de- 

 sirability of determining the temperature coefficient rather than assuming 



Actual experimental determination i* facilitated by the proportional 

 relation between the t- nt and the condu mea- 



sun r quantity gives both. if a temperature coeffi - 



must be assumed, the best value to take for average commercial 

 annexed copper wire is that given in the table for 100 per cent cor. 



a. -0.00428, a,, -0.00394, a,, -0.00386 



This is the value recommended for wire wound on instruments and ma- 

 they are generally wound with annealed wire and ex peri - 



its have show: ns due to the winding of the wire do 



not appreciably affect the temperature coefficient. 



If a value must be assumed for kard-drawn copper wire, the value 

 commended is that given in the table for 97.3 per cent conduct: 



a. -0.00415. Of,, -0.00383. a,, -0.00370 



The temperature coefficients in fahrenheit degrees are given by dividing 

 any a above by 1.8. Thus, the 20 deg. cent, or 68 deg. fahr. temperature 

 coefficient for copper of 100 per cent condu 0.00394 per deg. 



cent., or 0.00219 per deg. fahr. 



API P. HORSEPOWKK. 



361 v of the fact that a horsepower defined as 550 foot-pounds per 



second represents a power which varies slightly with the latitude 

 altitude (from 743.3 to 747.6 watts) and also in view of the fact that dif- 

 :it authorities differ as to the precise value of the horsepower in watts. 

 Ikt Standards Commtllee kas adopted 746 raits ax tkt ra/* of Ikt korsttmctr. 

 The number of foot-pounds per second to be taken as one horsepo* 

 therefore such a value at at lace as is equivalent to 746 watts; the 



number varies from 552 to 549 foot-pounds per second, being 550 at 5<> 

 latitude (London), and 550.5 at Washington. The Standards Comm 

 however, recommends that the kilowatt instead of the horsepower be used 

 generally as the unit of power. 



