Fig. 228. Cook Arrester
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Another central-office protector, which uses a mass of special metal composition for its heat producing element is that designed by Frank B. Cook and shown in Fig. 228. In this the carbon blocks are cylindrical in form and specially treated to make them "self-cleaning." Instead of employing a self-soldering feature in the sneak-current arrester of this device, Cook provides for electrically resoldering them after operation, a clip being designed for holding the elements in proper position and passing a battery current through them to remelt the solder.

In small magneto exchanges it is not uncommon to employ combined fuse and air-gap arresters for central-office line protection, the fuses being of the mica-mounted type already referred to. A group of such arresters, as manufactured by the Dean Electric Company, is shown in Fig. 229.

Fig. 229. Mica Fuse and Air-Gap Arresters
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Types of Subscribers' Station Protectors. Figs. 230 and 231 show types of subscribers' station protectors adapted to the requirements of central-battery and magneto systems. These, as has been said, should be mounted at or near the point of entrance of the subscriber's line into the premises, if the line is exposed outside of the premises. It is possible to arrange the fuses so that they will be safe and suitable for their purposes if they are mounted out-of-doors near the point of entrance to the premises. The sneak-current arrester, if one exists, and the carbon arrester also, must be mounted inside of the premises or in a protecting case, if outside, on account of the necessity of shielding both of these devices from the weather. Speaking generally, the wider practice is to put all the elements of the subscriber's station protector inside of the house. It is nearer to the ideal arrangement of conditions if the protector be placed immediately at the point of entrance of the outside wires into the building.