Alma record. (Alma, Mich.) 1878-1928, 1906-09-12
PROTECTION OF BUILDINGS
FROM LIGHTNING.
By Arthur r. Sawyer. B. S.. Z. E..
Professor of Physics and Elec-
trical Engineering at Michigan
Experiment Station.


trical Engineering at Michigan
Experiment Station.
This special bulletin is issued to
answer the many inquiries which
come to the college and station con-
corning the function Of lightning rods
and the proper methods Of construct
ing them.
1t is now supposed that lightning
flashes are of two distinct characters,
vertical fash or main discharge be-
tween the cloud and the ground, and
side discharge between the cloud
and the ground, precipitated as the
immediate consequence Of a main
flash between two opposed clouds.
An ordinary lightning rod properly
put up is fairly sure 10 protect against
the first fash mentioned, while to
protect against the second class OF
flashes would require complete
bird cage" well grounded, set down
over the building. 1t is manifesty
impossible TO put such a bird cage
over a building but we can approx
mate somewhat TO that condition
We have the words OF eminent
scientists to the effect that lightning
rods, properly put mp, do offer very
material protection, although they do
not render the house absolutely inn
munc to injury. Mr.. Kellingworth
Hedges, an eminent British authority,
is of the opinion that modern meth
obs Of installing lightning conductors
afford reasonable protection and that
the amount expended ON such pro-
lection should be proportional to the
value OF the property protected
The following method OF installing
lightning rods is suggested: Let the
rod start from one side, 90 up over
the building and down the opposite
side. thoroughly grounding both ends
as indicated below There should be
one rod up each of the two opposite
sides OF any cupOla or projection on
the roof, the rods TO 60 some two
feet or more higher than the projec-
tion and be connected with the main
rod Horizontal conductors should
inter-connect all vertical rods at the
roof ridge level and also at the
ground level All large masses OF
metal in or on the building should
| be grounded as directly as possible
Gas pipes and all large masses OF
metal should be kept away from the
| lightning conductors. The efficiency
of the lightning rod depends very
materially on its being well ground
ed. which means that il should be in
permanent connection with moist
earth The usual method of ground
ing is to dig hole down To earth
that is permanently moist Solder
the lighting rod TO a piece Of gas pipe
or to an old wash boiler and imbed
this larger metal i'll coke There must
| be ample carrying surface from the
surface OF the ground down into this
| mass OF coke 1t is suggested that
it is well To allow the caves OF the
house to discharge the water through
a drain tile into this mass OF coke
which is buried beneath the surface
10 keep it moist The only objection
! TO this suggestion Is that when a
thunder storm comes up after 4 long
dry spell, the coke is apt to be dry
in spite of this precaution. Any
method that will keep the coke moist
or secure adequate connection be
tween the lightning rod and moist
earth is sufficient.
rs to the metal OF which the light
ming rod is to be made. it is suggest
ed that the choice lies between iron
and copper.
In any event it should have ample
carry capacity, if OF iron, several
number six galvanized wires may be
used or 50 inch galvanized cable
such As telephone companies Use in
guying poles I'm iron rod is some
what more desirable than a copper
one because OF its inductance, but
joints are Liable To- rust and the rod