INSTALLATION OF FIXED EQUIPMENT 89 



1 PARTIALLY EXPOSED SUBSTATIONS 



Where it is absolutely certain that the line is nowhere exposed to accidental con- 

 tact with electric-light, power, or high-tension circuits (but only to lightning), each 

 telephone station should be considered as partially exposed, and nothing beyond the 

 No. 60-E protector used for protection. Where lightning is unusually severe, however, 

 either a 47-A line fuse, in addition to the 60-E protector, or a 58-F lightning protector 

 should be used. The former should be located immediately outside of the building 

 and attached to the main line wire in such a way that, when blown, the wire on the 

 side toward the line will fall away (Fig. 44). On a metallic line, where line fuses 

 are used, a fuse should be attached to each wire. When the 58-F, which is a combina- 

 tion of the 60-E protector with fuses, is used, a No. 48 asbestos mat should be mounted 

 back of all protectors and the slits in the fuses turned toward the mat.- The appear- 

 ance of the installation is much improved if the rough edges of all asbestos mats are 

 bound with brass or aluminium oilcloth binding tape, as in Fig. 84. 



Special provisions are required for the protection of the lookout sets (1336-J) 

 and the portable telephones. These are discussed in Section 75, 80, and 81. 



2 FULLY EXPOSED SUBSTATIONS 



A fully exposed substation is one on a line which may be exposed to accidental 

 contact with electric-light, power, or high-tension transmission lines. Even though 

 only a portion of a line is subject to such exposure all stations on it will be considered 

 as fully exposed. The 60-E protector with 47-A line fuse, or the 58-F protector, will 

 be used at these stations. In all cases where the line is exposed to a high-tension 

 voltage in excess of 1,800 volts the district inspector should be consulted in regard to 

 the additional protection. 



3 CONNECTIONS WITH FOREIGN LINES 



In general, it is not necessary to consider the exposure along other telephone lines 

 with which the Forestry Branch lines may connect, provided the connection is made 

 through a switchboard. If made by any other means, however, one of the above- 

 described protective methods will be used. 



4 LOCATION OF PROTECTORS 



It is dangerous to place protectors on or immediately adjacent to the telephone 

 sets. Always install the protector at least 2 feet away from the instrument, generally 

 at or very near the point of entrance to the building and as nearly over the ground 

 rod as possible. The 58-F protector should be mounted upon the wall so that the 

 fuses are vertical, and fastened in place by screws. It should not be exposed to water 

 or dampness or be placed outdoors. When the leading-in wires enter the building 

 above the door or window casing, the protector should be mounted so as to allow a 

 space of 1 in. between the protector and the casing. Where the wires enter at the side 

 of the door or casing, the protector should be mounted flush with the latter. It should 

 always be placed at least 12 in. from curtains, shades, or similar combustible materials 

 and should never be mounted directly above any such materials. 



Ordinarily only one mica should be used between each pair of protector blocks, 

 but in localities where lightning is excessive and the stations difficult of access two 

 micas may be inserted, thus increasing the air gap. Paper or other material should 

 never be substituted permanently. 



The 58-F protector should be connected as follows: Connect the leading-in wire 

 or wires to the fuse terminals marked L most dista-nt from the protector blocks, and 

 the inside line wires to the other end of the fuse terminals that is, the end nearer 



