The Washington herald., 1922-06-04
CHANGES
OFFER PROTECTION
TO ALL RADIO SETS
National Electric Code
May Alter Present
Rule sc.

This Is the concluding article on
the revision Of rule Sc of the Ma
tional Electrical code. It enabodies
a discussion of the proposed
changes as regards receiving sets
and transmitters.
These rules do not apply to radio
equipment installed on shipboarc
but have been prepared with refer
ence to land stations.
Receiving equipment:
a. Antenna-Indoor,r receiving an
tennas are not included within the
requirements Of this proposed rule,
which provides for the protection
of radio equipment against light
ming. Indoor receiving antennas
and auxiliary apparatus are, how
ever. included in the general re-
quirements covering the wiring of
signal systems. for IL is obviously
desirable to insure. for example. the
freedom of all receiving apparatus
from contact with electric power
circuits either inside or outside of
buildings.
Size of Antenna.
The size and material of which
the antenna is made should depend,
TO some extent, upon the length of
the span which the antenna must
bridge. 1t is suggested that for
the ordinary receiving antenna
about 100 feet long No. Il B. and S.
gage soft drawn copper wire can
safely be used.
The requirements covering splices
and Joints In the antenna span are
for the purpose of avoiding acct
dental falling OF such wires upon
light or power wires of less than
500 volts where 1t is found neces-
sary to cross such lines. The rules.
1t Will be noted. permit crossings
with lines of 500 volts or less, IL
they do not happen to be trolley
wires or feeders to trolley wires.
The interchangeable use Of cop
per and of approved copper-clad
conductor is suggested on account
of the fact that these two kinds of
wire are practically equivalent in
their conductivity for high-fre-
quency current.
Guard Against Wet weather.
b. Lead-in wires-No mention is
made of the insulation from the
building of the receiving antenna
or lead-in wire except that this
lead-in wire should be run through
bushing. The latter provision is
chiefly to protect the wiring against
the possibility of short-circuiting
with electric power lines which
may run in the wall and whose
location may be unknown to the
persons installing the radio equip
ment. This requirement serves also
to protect the antenna leadin wire
against contact with metal lath or
other metal parts of the buildings.
From a signaling standpoint 1t is
desirable to use insulators for re-
ceiving antennas in order that wet
weather may not cause the antenna
to become partly short-circuited to
the ground.
C.. Protective Device-The require
ment for a protective device to be
connected between the antenna and
ground terminals Of the receiving
set is for the purpose of carrying
lightning discharges or less violent
discharges caused by induction or
by atmospheric electricity to the
ground with a minimum chance of
damage to the receiving apparatus.
building or operator. II a fused
lightning arrester Is used II makes
It less likely that the antenna ter
minal of a receiving set will be put
at a high voltage in case the an
tenna falls upon an electric light or
power wire. The absence of the
fuse. on the other hand, makes II
possible for the antenna, IL II acci-
dentally falls across the power
wires. to become fused at the point
of contact and thus fall to the
ground and eliminate the hazard.
The antenna terminal of the re-
ceiving set should be connected to
the point Of junction of the fuse
with the arrester.
Approved Devices Listed.
Lightning arresters may be used
inside the building. and in such a
case they will receive better protec-
tion from moisture and mechanical
injury than lightning arresters
placed on the outside OF a building
wall.
Protective devices Of reliable manu-
facture are approved by the Under
writer's Laboratories. and can be de-
pended upon to operate at the re-
quired voltage. The use of a cheaply
constructed home made arrester, Is
not recommended. since 1t may easily
get out OF order and fail to operate
at the low voltage which is desirable.
Arresters should be inclosed in such
a way as to protect the breakdown
gap from dust. One disadvantage of
the vacuum tube type Of arrester Is
that 1t may cease to function with
out giving warning that 1t is in
operative. A list of the approved
protective devices and ground clamps
is contained in the List of Inspected
Electrical Appliances" published by
the Underwriters' Laboratories. This
list Is revised semi-annually and may
be consulted upon application to the
principal office of the Underwriters
Laboratories. Inc, 207 East Ohio