The Standard Electrical Dictionary / A Popular Dictionary of Words and Terms Used in the Practice of Electrical Engineering

by T. O'Conor Sloane

Fig. 68. BRUSH HOLDER.
Brushes, Lead of.
In a dynamo electric generator, the lead or displacement in advance of
or beyond the position at right angles to the line connecting the poles
of the field magnet, which is given the brushes. In a motor the brushes
are set back of the right angle position, or are given a negative lead.
(See Lag.)
91 STANDARD ELECTRICAL DICTIONARY.
Brush Holders.
The adjustable (generally) clutch or clamps for holding the commutator
brushes of a dynamo, which keep them in contact with the commutator, and
admit of adjustment by shifting backward and forward of the brushes to
compensate for wear. They are connected to and form part of the rocker,
q. v. By rotating the latter the brush-holders and brushes are carried
in one direction or other around the commutator, so as to vary the lead
as required.
Brush, Pilot.
A third brush, used for application to different parts of a revolving
armature commutator to determine the distribution of potential
difference between its different members. (See Curve of Distribution of
Potential in Armature.) One terminal of a volt-meter is connected to one
of the regular brushes, A, of a dynamo; the other to a third brush, p,
which is pressed against different portions of the commutator of the
dynamo. The readings of the volt-meter are plotted in a curve of
distribution of potential.

Fig. 69. PILOT BRUSH.
Brush, Rotating.
Brushes for taking off the current from dynamo commutators, or giving
current connection to motors, whose ends are in the form of rollers
which rotate like little wheels, and press against the commutator
surface.
Brush, Third.
A third brush is sometimes provided in a dynamo for regulating purposes.
Applied to a series machine it adjoins one of the regular brushes and
delivers its current to a resistance, to whose further end the regular
circuit is connected. By a sliding connection the resistance is divided
between the third brush circuit and the regular circuit, and by varying
the position of this contact regulation is obtained.
It is to be distinguished from the pilot brush used for determining the
characteristic of the commutator, although based on the same general
principles.

Fig. 70. THIRD BRUSH REGULATION.
92 STANDARD ELECTRICAL DICTIONARY.
Brush, Wire Gauze.
A collecting or commutator brush for a dynamo or motor, which brush is
made of wire gauze rolled up and compressed into shape.
Buckling.
The bending up and distortion of secondary battery plates. It is largely
due to over-exhausting the batteries. Where the E. M. F. is never
allowed to fall below 1.90 volt it is far less liable to occur.
Bug.
Any fault or trouble in the connections or working of electric
apparatus.
Bug Trap.
A connection or arrangement for overcoming a "bug." It is said that the
terms "bug" and "bug trap" originated in quadruplex telegraphy.
Bunsen Disc.
In photometry, the Bunsen Disc is a piece of paper upon whose centre a
spot is saturated with melted paraffin, or a ring of paraffined surface
surrounds an untouched central spot. If placed in such a position that
it receives an equal illumination on each side, the spot almost
disappears. It is used on the bar photometer. (See Photometer, Bar.)
Synonym--Grease Spot.
93 STANDARD ELECTRICAL DICTIONARY.
Buoy, Electric.
A buoy for use to indicate channels or dangers in harbors and elsewhere,
which carries an electric light, whose current is supplied by cable from
shore. It has been proposed to use glass tubes exhausted of air and
containing mercury, which, as moved by the waves, would produce a
luminous effect. A fifty-candle power incandescent lamp is an approved
source of light.
Burner, Electric Gas.
A gas burner arranged for the flame to be lighted by electricity. It
takes a great variety of forms. In some cases a pair of terminals are
arranged near the flame or a single terminal is placed near the metal
tip, the latter forming one of the terminals. The spark is generally
produced by an induction coil, or a spark coil. The gas may first be
turned on and the spark then passed. Sometimes the turning of the gas
cock of an individual burner makes and breaks a contact as it turns, and
thereby produces simultaneously with the turning on of the gas a spark
which lights it.
Another form is wholly automatic. A pair of electro-magnets are attached
below the base of the burner, one of which, when excited, turns on the
gas, and the other one when it is excited turns it off. At the same time
a spark is produced with the turning on of the gas so that it is
lighted. Thus, by use of a automatic burner, a distant gas burner can be
lighted by turning an electric switch. An out-door lamp may be lighted
from within a house.
The increasing use of electric incandescent lamps, lighted by the
turning of a switch, tends to displace electric gas burners. The latter
have been classified into a number of types depending on their
construction.
Burners are sometimes connected in series with leads from an induction
coil. Then the gas is turned on all at once, and a succession of sparks
passed until the gas is all lighted. The ignition is practically
instantaneous.
Button, Push.
A species of switch which is actuated by the pressure of a button. In
its normal position the button is pressed outwards by a spring, and the
circuit is open. When pressed inwards, it closes the circuit. When
released it springs backward and opens the circuit again.
They are principally used for ringing bells. If the latter are of the
automatic type, they ring as long as the button is pressed.
For door-bells and room-bells, the button often occupies the center of a
rosette of wood or bronze or other ornamental piece. Sometimes, as shown
in the cut, they are constructed for use on floors to be pressed by the
foot. The general principle of their construction is shown, although the
method of making the contact varies.
Synonym--Press Button.

Fig. 71. FLOOR PUSH BUTTON.
94 STANDARD ELECTRICAL DICTIONARY.
Burning.
(a) In a dynamo, the production of shifting and temporary arcs between
the commutator and brushes, which arcs produce heat enough to injure the
parts in question.
(b) In electro-plating, a defect due to too strong a current in
proportion to the strength of solution and area of electrodes. This
gives a black or badly-colored deposit.
Bus Rod.
A copper conductor used in electric lighting or power stations, to
receive the current from all the dynamos. The distributing leads are
connected to the bus wires.
In the three-wire system there are three; in the two-wire system there
are two bus wires.
The name is undoubtedly derived from "omnibus."
The bus wires may be divided into positive, negative, and, in the
three-wire system, neutral bus wires.
Synonyms--Omnibus Rod, Wire, or Bar--Bus Bar, or Wire.
Buzzer.
An electric alarm or call produced by a rapid vibration of electric make
and break mechanism, which is often magnified by enclosure in a
resonating chamber, resembling a bell, but which is not struck or
touched by the vibrating parts. Sometimes a square wooden box is used as
resonator.

Fig. 72. BUZZER.
95 STANDARD ELECTRICAL DICTIONARY.
B. W. G.
Abbreviation for Birmingham Wire Gauge. (See Wire Gauge, Birmingham.)

C.
(a) Abbreviation for Centigrade, as 100 C., meaning 100 Centigrade. (See
Centigrade Scale.)
(b) A symbol of current or of current strength. Thus in the expression
of Ohm's law C = E/R. C indicates current strength or intensity, not in
any fixed unit, but only in a unit of the same order in which E and R
are expressed; E Indicating electro-motive force and R resistance.
Cable.
(a) Abbreviation for Cablegram, q. v.
(b) v. It is also used as a verb, meaning to transmit a message by
submarine cable.
(c). An insulated electric conductor, of large diameter. It often is
protected by armor or metallic sheathing and may be designed for use as
an aerial, submarine, subterranean or conduit cable. A cable often
contains a large number of separately insulated conductors, so as to
supply a large number of circuits.
Cable, Aerial.
A cable usually containing a large number of separately insulated wires,
and itself insulated. It is suspended in the air. As its weight is
sometimes so great that it could not well sustain it, a suspending wire
is in such cases carried along with it, to which it is suspended by
cable hangers, q. v.
Cable Box.
A box for receiving underground cable ends and connecting the separate
wires of the cable to air-line wires. It is often mounted on a pole,
which forms the starting point of the air-line portion of the system.
Cable, Bunched.
A cable containing a number of separate and individual conductors. In
some forms it consists virtually of two or more small cables laid
tangent to each other and there secured. Thus each in section represents
two or more tangent circles with the interstice solidly filled with the
metal sheathing.
Cable, Capacity of.
The electrostatic capacity of a cable. A cable represents a Leyden jar
or static condenser. The outer sheathing or armor, or even the more or
less moist coating, if it is unarmored, represents one coating. The wire
conductors represent the other coating, and the insulator is the
dielectric.
The capacity of a cable interferes with its efficiency as a conductor of
broken or interrupted currents, such as are used in telegraphy or
telephoning. As each impulse or momentary current is sent into the line,
it has to charge the cable to at least a certain extent before the
effects of the current are perceptible at the other end. Then the cable
has to discharge itself. All this creates a drag or retardation.
The capacity of a cable is used to determine the locality of breaks in
the continuity of the conductors. The capacity per unit of length being
accurately known, it is obvious that, if the conductor breaks without
disturbance of the insulator, the distance of the break from the end can
be ascertained by determining the capacity of the cable from one end.
This capacity will be in proportion to the capacity of a mile, a knot or
any fixed unit, as the distance to the break is to the length used as
standard.
96 STANDARD ELECTRICAL DICTIONARY.
Cable Core.
The conductors of a cable. They are generally copper wire. In a
telephone cable they may be very numerous and insulated from each other.
In ocean cables they may be a group of bare wires twisted or laid
together. Sometimes the conductors are arranged for metallic circuits,
each pair being distinguished by special colored windings.
Cable, Duplex.
A cable containing two wires, each with separate insulation, so as to be
virtually two cables, laid and secured parallel and side by side.
Cable, Flat.
A cable, flat in shape, so as to lie closely against a wall or ceiling.
Cablegram.
A message which has been transmitted or is to be transmitted by a
submarine cable. It is sometimes called a cable.
Cable Grip.
A grip for holding the end of a cable, when the cable is to be drawn
into a conduit in a subway. It is an attachment to provide the cable
with an eye or loop. Its end is a split socket and embraces the end of
the cable, and is secured thereto by bolts driven through the cable end.
In drawing a cable into a conduit a capstan and rope are often used, and
the rope is secured to the cable end by the grip.