80 METHODS OF COMMUNICATION FOR FOREST PROTECTION 



Transmission lines should always be crossed at a right angle. Unless the dis- 

 trict inspector specifies otherwise, or unless the transmission company has provided 

 special and safe protection, the crossing will be made as follows: Dead-end the tele- 

 phone line on each side of the transmission line, at least 150 ft. from the cross! im. 

 and brace or guy the lasst poles. The actual crossing should be made underground 

 by means of an extra heavily insulated, rubber-covered, braided, and weather-proofed 

 No. 14 B. and S. copper wire run through a 1-in. iron pipe, starting at a point on 

 the pole about 8 ft. above the ground. The joints in the pipe should be made water- 

 tight by the use of red lead, and 1 an inverted "U" attached to the top of each pipe, 

 so that rain-water cannot follow the wire. The rubber-covered wire should extend 

 up the pole and be connected to the line wire. In. crossing with a metallic circuit both 

 wires may be run in the same pipe. This method is illustrated in Fig. 37. 



If considerable blasting would be required to put the iron pipe underground 

 below the frost line, it may be laid across the surface of the rock, providing it is 

 covered with an earth embankment to a depth of 2 or 3 ft. 



If permission is requested for a high-tension transmission line to cross an existing 

 forest reserve telephone line, the Director will require that the transmission line be so 

 constructed as to provide safe and approved protection for the Forestry Branch line. 

 Where the telephone line is exposed to voltage in excess of 5,000 volts Order 231 of the 

 Board of Railway Commissioners for Canada for overhead crossings of electric-light 

 and power lines will be used as a basis for determining suitable protection. (See 

 Appendix D.) 



6 SUBMARINE 



In many regions, particularly in the eastern forests of Canada, the necessity 

 for crossing wide bodies of water with telephone lines arises with great frequency. 

 Often many miles of aerial construction can be saved by a comparatively short sub- 

 marine span. If properly laid with suitable material, submarine lines involve almost 

 no maintenance charges. Cost of installation is usually very low. Against these 

 advantages, however, there are certain serious objections to submarine lines which 

 must be fully considered. 



A suitable conductor, that may be depended upon to give uninterrupted service 

 is likely\ to be very costly, particularly where there is any current in the body of 

 water to be crossed. 



A break or leak in a submarine cable causes a complete interruption of the 

 service and it is impossible to make temporary emergency repairs as with land lines, 

 but the cable must be raised, often at considerable expense, and permanent repairs 

 made before service can be resumed. 



A submarine cable has a very great electro-static capacity, many times greater 

 than the same length of overhead wire, and the practical result is that a mile of such 

 caole is equivalent to approximately 2.3 miles of well-built, standard land line. The 

 use of even short submarine spans, therefore, in long land' lines must be carefully 

 considered, not only from the standpoint of first cost and maintenance but also from 

 the standpoint of their effect on the operating efficiency of the line. 



No submarine cables shall be purchased unless authorized by the Director^ and 

 on specifications furnished by him, and no such cable shall be installed until the 

 proposed site has been inspected and approved by the district inspector. As sub- 

 marine cables for still-water spans over one-half mile in length, or for spans of any 

 length in water having a perceptible current, may have to be manufactured to special 

 specifications, field officers will be expected to report all such cases to the district 

 inspector at least one year before construction is contemplated. In reporting, state 

 length of water-span, character of current, if any, nature of bottom at each shore 

 and in the middle of the span, depth of water at intervals from shore to shore, annual 

 variation in water level, if any; and state whether or not the water is contaminated 

 with industrial acids or other corrosive substances or is salt or brackish. A map of 



