The Washington herald. [volume] (Washington, D.C.) 1906-1939, 1922-04-16
RADIO SETS NEED
PROTECTION FROM
LIGHTNING DANGER
One Unit Arrester May
Sidetrack Electric
Charges.
MAY GUARD HOUSE
Spark Gap Always Should Be
/. Used With Ground
r Switch.
MAY GUARD HOUSE

lnunoer showers during the past
few days were reminders of the ne
cessity for adjusted protection
against lightning for both the ra-
do set and the house. II the ap-
paratus is properly protected no
damage will result during a thun-
der shower. whereas IL no lightning
connections are made the aerial
will provide an easy and sure path
for the electricity to follow and
destroy property, possibly life.
The most modern and convenient
way of meeting requirements Of
the National Board of Fire Under
writer's Is to purchase in one unit
a lightning arrester which permits
the passage of normal currents
while by means of an air gap or
vacuum 1t provides a side path for
an overcharge of electricity into
the earth. This Is explained in the
case of the Brack arrester shown
in B above. The function of the
lightning arrester may be COM
pared to a safety valve in a steam
system, when the voltage becomes
too high for the circuits to carry
safely. the lightning arrester will
operate. sidetracking this high
voltage into the earth. The above
arrester therefore and other makes
such as the Keystone may be con-
nected outside or inside the build
ing as shown in (a) and OBJ re-
spectively. Local radio dealers
have such units for sale.
Protect Ground Switches.
For the benefit of many persons
who have purchased and installed
g W NJ
their complying with specifications
and their own needs for projection
against lightning the following in
formation is given by the National
Board of Fire Underwriters
I'm radio stations used for receiy-
ing only the grounding switch may
be replaced by a similarly mounted
and grounded spark gap az inch or
iess) or vacuum type lightning ar
roster. The current-carrying pats
OF devices must be inches clear Of
the building wall"
As regards the grounding switch
referred to in the above specification,
the rule is. The switch shall be a
knife switch OF approved design, the
blade of which must have a peri
phery of not less than q Of an inch,
and when open the current-carrying
parts to which the aerial and ground
connection wire are attached will be
separated at least inches. The base
OF the switch must be OF a material
suitable for high frequency service.
Slate will not be approved" A knife
switch answering these requirements
and placed conveniently is shown
above on the window casing. Such
switch will stand a charge of 500
volts-100 amperes-as required by
law.
Equally important are switch con-
nections to both ground and set. The
connecting wires and all the sizes
are plainly indicated above. Note
that in passing through the wall OF
the building 'fnsulators must he in
stalled to maintain the conductors
at least inches clear of the surface
Of the building wall In passing the
aerial conductor through the side of
the building a continuous tube or
pushing must be used-and must ex-
tend inches beyond the surface of
the wall on both sides"
the grounding switch Of course,
Is connected at one end to the aerial
lead-in and on the other end to the
ground. As regards this ground con-
nectlon. section reads: Aerial
conductors must be effectively and
permanently grounded at all times
When the station is not in operation"
and continues, ground to a water
piping system il avaiIable-not to
rails of electric railway circuits"
The method OF attaching the ground
wire is then explained: The con-
nection to metallic piping systems
must be either by the use of an ap-
proved ground clamp bolted to the
pipe after IT has been freed from all
rust and scale or by screwinE tight
~ into the pipe or pipe fitting a
brass plug having a lug from the
ground conductor or by other euuiva
lent means. The ground wire must
De attached to the plug by means of
solder or an approved solderless con-
hector. The point of connection
should be accessible"
Defines Ground Requirements.
There is often a question as to
what constitutes a ground" This
definition is given: Artificial
grounds (used when water pipes as
explained above are not accessibIe).
should be located where practica BILE
below permanent moisture level.
Each ground must present not less
than four square feet surface to ex-
terror soil. Areas where ground
water level is close to the surface
should be used when available
Where ground plates are used they
should be at least No. is Stubs
gauge copper: when driven pipes
are used they should be of galvan-
lied iron and not smaller than one
inch internal diameter. When cast