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 po ible 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 nece ity 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. IMG:384091999325875926_fig230_t.gif.png:Illustration_ Fig. 230. Western Electric Station Arrester Fig. 230. Western Electric Station Arrester View full size illustration. IMG:384091999325875926_fig231_t.gif.png:Illustration_ Fig. 231. Cook Arrester for Magneto Stations Fig. 231. Cook Arrester for Magneto Stations View full size illustration. Ribbon Fuses . A point of interest with relation to tubular fuses is that in some of the best types of such fuses, the resistance material is not in the form of a round wire but in the form of a flat ribbon. This arrangement disposes the nece ary amount of fusible metal in a form to give the greatest amount of surface, while a round wire offers the least surface for a given weight of metal—a circle encloses its area with le periphery than any other figure. The reason for giving the fuse the largest po ible surface area is to decrease the likelihood of the fuse being ruptured by lightning. The fact that such fuses do withstand lightning discharges much more thoroughly than round fuses of the same rating is an interesting proof of the oscillating nature of lightning discharges, for the density of the current of those discharges is greater on and near the surface of the conductor than within the metal and, therefore, flattening the fuse increases its carrying capacity for high-frequency currents, without appreciably changing its carrying capacity for direct currents. The reason its capacity for direct currents is increased at all by flattening it, is that the surface for the radiation of heat is increased. However, when enclosed in a tube, radiation of heat is limited, so that for direct currents the carrying capacity of fuses varies closely with the area of cro -section.