The practical telephone handbook and guide to the telephonic exchange (1906)
Poole, Joseph · New York, Macmillan Co. · leaf 312
U-shaped mica and the plug of fusible metal. The heat-coil (seen in section) isplaced between the springs as shown, the inner spring restingagainst a small brass collar soldered near the end of a thinbrass rod by fusible metal. When the current in the coilbecomes too great (more than *33 ampere)… … Fig. 290.—Plain Scale £ 286 PRACTICAL TELEPHONE HANDBOOK silver strips, riveted on the thick iron bar, which forms thesupport for the whole strip. The resistance of the heat coil is 375 ohms. All thebars are connected to earth, and thus the line wire becomesdirectly earthed when the fuse operates.…
Telephone
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