14 BELL SYSTEM TECHNICAL JOURNAL 



(2) Maxinuini line resistance, including subscriber's station, 

 1000 ohms. 



(3) Resistance across line to represent maximum insulation leak- 

 age, 10,000 ohms. 



(4) Winding of rela>- 12,000 turns, 2000 ohms ± 5 per cent. 



(5) Minimum operating ampere turns = 



Turns X Minimum Voltage _ 12,000 X 20 _-_ , 

 Maximum Resistance ~ 1000 + 2100 " " ' ' 



(0) Maximum releasing ampere turns = 



Turns X Maximum Voltage 12,000 X 28 



= 28.2. 



Leak Resistance + Minimum 10,000 + 1900 

 Relay Resistance 



Reference to the circuit will show that the line rela\- must release 

 on a low resistance loop in case the subscriber flashes the line lamp 

 to attract the operator's attention. Due to residual magnetic ef- 

 fects, a relay does not release after operation on short loops over 

 which the operating current is high as quickly as it does after operat- 

 ing on long loops, with a lower current in the winding. It is, there- 

 fore, necessary to specify the maximum ampere turns the line rela>- 

 may receive and adjust it to release inimediatcK- afterward with 

 the maximum leak across the line. 



12,000X28 ,^^„ 

 (7) Maximuni ampere lurns = = 176.8. 



In addition : 



(a) The relay must close one set of contacts which controls a 

 signal lamp as shown in the circuit. 



lb) Contacts must carry the energ>- for lii;htini; the lamj) with- 

 out undue sparking, sticking or wear. 



(c) The relay ninsi operate reli,d)l\- on 77.4 ampere turns. 



(d) The rela>- niii^t itKmm' on '_'S.2 ampere turns irnmediateK- 

 after operating on 17(). 8 ampere turns. 



(e) As there is a constant pntential lietween \\inclinj;s, the coil 

 must be protecti'd from corrosion, >o the materials chosen tor the 

 construction nf the relay must not contain substances which tend to 

 encourage or assist electrolytic action. 



It was found that the line relay introduced hi,i;li maintenance 

 charges because of the knife edge armature hinge and the close adjust- 

 ment required. The armature being coniparati\ely light in weight. 



