Instead of using a wire-wound resistance element in heat-coil
construction some manufacturers employ a mass of high-resistance
material, interposed in the path of the current. The Kellogg Company
has long employed for its sneak-current arrester a short graphite rod,
which forms the resistance element. The ends of this rod are
electroplated with copper to which the brass terminal heads are
soldered. These heads afford means for making the connection with the
proper retaining springs.

[Illustration: Fig. 228. Cook Arrester]

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.

[Illustration: Fig. 229. Mica Fuse and Air-Gap Arresters]

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