JOINT DEVELOPMENT AND NOISE FREQUENCY INDUCTION 203 



four-wire systems with various arrangements of neutral grounding, 

 data on coupling between various typical arrangements of these sys- 

 tems and telephone cable circuits, and information on susceptiveness 

 characteristics of telephone systems, including unbalances of lines and 

 apparatus. To facilitate the use of this information in the day-by-day 

 coordination problems handled by the operating companies, a summar- 

 izing report » entitled "Short-Cut Methods for Calculating Noise in 

 Local Telephone Subscribers' Circuits in Cable Due to Exposures to 

 Power Distribution Circuits" has been prepared. This report presents 

 empirical formulas for estimating noise-frequency induction and in- 

 cludes a brief discussion of the technical factors involved and the 

 approximations underlying the formulas. Means are described for 

 reducing influence by the control of triple-harmonic exciting currents 

 and load unbalances of power distribution circuits, and for reducing 

 susceptiveness by grounding telephone cable sheaths and by controlling 

 the unbalances of the telephone station equipment. The information 

 should be useful to engineers of the operating companies in the coopera- 

 tive planning of routes to avoid induction troubles. 



While a large part of the experimental work connected with the prob- 

 lem of joint use of local open-wire subscribers' circuits and power dis- 

 tribution circuits has been completed, the detailed technical reports 

 have not yet been completed for publication. However, a summar- 

 izing report ^° which it is believed will largely fill the needs of the engi 

 neers of operating power and telephone companies has been completed. 

 This is entitled "Short-Cut Methods for Calculating Noise in Open- 

 Wire Subscribers' Circuits Due to Joint Use Exposures to Power Dis- 

 tribution Circuits." 



Three reports have been issued dealing with the problem of coordina- 

 tion of open-wire toll circuits and overhead transmission and distribu- 

 tion lines. The first ^^ discusses the "Termination of Isolated Ex- 

 posure Sections to Obtain Normal Metallic-Circuit Currents," which 

 affords a means of taking into account the shielding effects present 

 when the line is in normal operating condition. The second report ^- de- 

 scribes "A Method of Measuring the Balance of Open-Wire Telephone 

 Circuits with Respect to Longitudinal-Circuit Induction," which should 

 be useful to the field in the making of special tests and in supplying 

 statistical data of value for estimating noise effects on open-wire line 

 circuits. The third report.^^ dealing with "Methods of Measuring 

 Noise on Open-Wire Toll Circuits," is a detailed presentation of the 

 various types of tests for studying noise problems on toll lines, and 

 includes a discussion of the method of analyzing the test data. 



Another report '" deals with "The Effects on Inductive Coordination 

 of Generators Feeding Directly on the Line and Operating with 



