92 METHODS OF COMMUNICATION FOR FOREST PROTECTION 



4 MULTIPLE GROUNDS 



The following instructions taken from the Telephone circular of District No. 5, 

 United States Forest Service, apply to stations where several lines converge: 



" Where more than one line enters a station to telephones, extension bells, or a 

 switchboard, all the instruments having the same ringer resistance may sometimes 

 be grounded on the same ground rod or coil, provided the electrical contact to the earth 

 is satisfactory. 



" The efficiency of a common ground should first be tested before making perma- 

 nent connections to it. Where the rod or coil is immediately adjacent to the instru- 

 ments simply connect it to the instrument by a temporary wire. All points of connec- 

 tion should be clean and tight. If a satisfactory ground cannot be found nearby, the 

 test may be made by stringing No. 9 wires to different places which appear to be satis- 

 factory until good grounds are found. (Test by attaching one instrument to the wire, 

 the wire leading to the experimental grounding-place, and if satisfactory results are 

 obtained connect in turn lead wires from each additional instrument.) Cross-talk 

 between the lines may be heard even if the ground is good, but it should not be pro- 

 nounced. When a signal is rung over one of the lines the bells should not cross-ring ; 

 that is, two bells or more should not ring with the switches open between the respective 

 lines. If the cross-talk is loud and the bells cross-ring, or if cross-talk is loud in the 

 absence of cross-ringing, inadequate ground to carry the full number of instruments 

 attached is indicated. Two or more wires leading to grounds should not closely parallel 

 one another. 



" Further experiments should be made by disconnecting one instrument at a time 

 from the lead wire, followed by a test until the cross-ringing is eliminated and the 

 cross-talk either eliminated or much weakened. Only in exceptional cases, if ever, 

 can cross-talk be entirely eliminated where several grounded lines enter the same sta- 

 tion. Seek additional ground or grounds for lines that were disconnected. 



'"It may be necessary in some cases, in order to get satisfactory service, that 

 grounds be separated as much as half a mile. The expense, however, of locating effi- 

 cient grounds and of installing connecting facilities is justified, because instrument 

 installation is a failure unless good grounds are made." 



Section 74 Wiring 



To ensure good service, instruments on both grounded and metallic lines must be 

 installed in the proper manner. Figs. 42, 44, 45, and 46 illustrate graphically the 

 method of making the entire installation. 



Before beginning work, means should be taken to determine the arrangement that 

 will be the simplest, the most economical, and the easiest to maintain. 



1- OUTSIDE OF BUILDING 



(a) Leading -in wires. If possible, the telephone should be located on the same side 

 of the building as the pole from which the branch line originates. The wire from 

 the line should be dead-ended on a bracket and insulator attached to the outside of 

 the building. A line should never be attached to a building directly from a tree, and 

 not more than 50 ft. of No. 9 iron wire should intervene between the building and 

 the nearest pole. Set an extra pole or use insulated copper wire. Try to have the 

 pull on the bracket attached to the side of the building parallel to the wall, and not 

 at right angles, and always rake the bracket slightly against the pull. 



The point where the wire enters the building should be as near as practicable to 

 a permanent ground, and each ground wire should pass through the wall of the building 

 in a separate porcelain tube, spaced at least 2J ins. from the other tubes, and sloping 

 upward from the outside. Under some conditions circular loom may be a satisfactory 

 substitute for the porcelain tube, though it should not be used without permission from 



