of individual parts
for multiple switchboards is the relay. The necessity for reliability of
action in these is apparent, and this means that they must not only be
well constructed, but that they must be protected from dust and moisture
and must have contact points of such a nature as not to corrode even in
the presence of considerable sparking and of the most adverse
atmospheric conditions. Economy of space is also a factor and has led to
the almost universal adoption of the single-magnet type of relay for
line and cut-off as well as supervisory purposes.

[Illustration: Fig. 361. Type of Line Relay]

[Illustration: Fig. 362. Type of Cut-Off Relay]

The Western Electric Company employs different types of relays for line,
cut-off, and supervisory purposes. This is contrary to the practice of
most of the other companies who make the same general type of relay
serve for all of these purposes. A good idea of the type of Western
Electric line relay, as employed in its No. 1 board, may be had from
Fig. 361. As is seen this is of the tilting armature type, the armature
rocking back and forth on a knife-edge contact at its base, the part on
which it rests being of iron and of such form as to practically
complete, with the armature and core, the magnetic circuit. The cut-off
relay, Fig. 362, is of an entirely different type. The armature in this
is loosely suspended by means of a flexible spring underneath two
L-shaped polar extensions, one extending up from the rear end of the
core and the other from the front end. When energized this armature is
pulled away from the core by these L-shaped pieces and imparts its
motion through a hard-rubber pin to the upper pair of springs so as to
effect the necessary changes in the circuit.

[Illustration: Fig. 363. Western Electric Combined Line and Cut-off
Relay]

[Illustration: Fig. 364. Western Electric Supervisory Relay]

[Illustration: Fig. 365. Line Relay No. 10 Board]

Much economy in space and in wiring is secured in the type of
switchboards employing cut-off as well as line relays by mounting the
two relays together and in making of them, in fact, a unitary piece of
apparatus. Since the line relay is always associated with the cut-off
relay of the same line and with no other, it is obvious that this
unitary arrangement effects a great saving in wiring and also secures a
great advantage in the matter of convenience of inspection. Such a
combined cut-off and line relay, empl