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THE BELL SYSTEM TECHNICAL JOURNAL, MAY 1953 



is very high. Tests to disclose insulation defects in inside wiring are made 

 when the weather is clear with low outside humidity at which time 

 leakages in other parts of the exchange plant will rarely be found. 



TIP AND RING GROUND TEST 



The "tip and ring ground" test can be made in three ranges of sensi- 

 tivity as shown in Table I. The arrangement of the test circuit for this 

 type of test is shown in Figure 6. The first test condition, Fig. 6 (a), 

 measures the combined leakage resistance from tip and ring to ground. 

 The tip and ring are connected together therefore leakage across the 

 pair is not indicated. This eliminates practically all of the drop wire 



TIP 



CONTACT OPENED 

 DURING TEST 



(b) 



FIRST TEST CONDITION MEASURES 

 COMBINED TIP TO GROUND AND 

 RING TO GROUND RESISTANCE 



RETEST AFTER FAILURE ON 

 COMBINED TEST MEASURES 

 RING TO GROUND RESISTANCE 



Fig. 6 — Tip and ring ground test. 



leakages. If a failure is indicated on the first test condition, a re-test is 

 made under the condition shown in Fig. 6 (b) to check only the resistance 

 from ring to ground. If the ring tests clear it is known that the leakage 

 is from tip to ground. This kind of test is of particular value in checking 

 terminal face plate leakages which are predominately leakages from tip 

 to ground. This type of test can also be used to check that tip con- 

 ductors on party lines in message rate areas are free of low resistance 

 grounds which might result in wrong party identification on calls made 

 by the ring party. 



FEMF TEST 



The FEMF (foreign e.m.f.) test is used to measure leakages in cable 

 to detect sheath breaks. These leakages are high resistance compared to 

 other leaks which may be present across the pair connected for test or 

 from the pair to ground. To make the latter ineffective so as not to 



