irection. Fuses are adapted to open
circuits when the currents in them are too great. The best type is that
in which the operation of the fuses sounds or shows an alarm, or both.

=Power-Plant Circuits.= The circuit arrangement of central-office power
plants is subject to wide variation according to conditions. The type of
telephone switchboard equipment, whether magneto or common-battery,
automatic or manual, will, of course, largely affect the circuit
arrangement of the power plant. Fig. 417 shows a typical example of good
practice in this respect for use with a common-battery manual
switchboard equipment. Besides showing the switches for handling the
various machines and the charge-and-discharge leads from the storage
battery, this diagram shows how current from the storage battery is
delivered to various parts of the central-office equipment.

[Footnote A: The instructions given later in this chapter are for
batteries of this make, although they are applicable in many respects to
all types commonly used in telephone work.]

CHAPTER XXXIII

HOUSING CENTRAL-OFFICE EQUIPMENT

=The Central-Office Building.= Proper arrangement of the central-office
equipment depends largely upon the design of the central-office
building. The problem involved should not be solved by the architect
alone. The most careful co-operation between the engineer and the
architect is necessary in order that the various parts of the telephonic
equipment may be properly related, and that the wires connecting them
with each other and with the outside lines be disposed of with due
regard to safety, economy, and convenience. So many factors enter into
the design of a central-office building that it is impossible to lay
down more than the most general rules. The attainment of an ideal is
often impossible, because of the fact that the building is usually in
congested districts, and its very shape and size must be governed by the
lot on which it is built, and by the immediate surroundings. Frequently,
also, the building must be used for other purposes than those of a
telephone office, so that the several purposes must be considered in its
design. Again, old buildings, designed for other purposes, must
sometimes be altered to meet the requirements of a telephone office, and
this is perhaps the most difficult problem of all.

The exterior of the building is a matter that may be largely decided by
the architect and owner after the general charac