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50 THE COAL TRADE BULLETIN.
while not so good as if installed on a timber or a
small block, still it has proven satisfactory in service.
The insulation resistance of the hanger
is the same as that of an expansion bolt hanger
and, consequently, leakage would be the same.
Expansion bolt hangers are provided with a
boss into which the end of the expansion bolt may
be screwed. The hanger is usually provided with
a hexagonal body so that a wrench may be applied.
Spikes and nails should not be used for attaching
hangers of any kind to their supports. Steel
mine limbers are rapidly coming into use for timbering
main entries, and a very good installation
of trolley and feeder may be made by fastening the
hangers directly to the bottom of the 1 beams.
Clamps for fastening the hanger to the 1 beams
are now being placed on the market.
D. The subject of proper placing of a trolley
frog or switch pan. as it is sometimes called, has
frequently been brought to the writer's attention.
and on account of various sizes of locomotives
used, it is a rather difficult matter to etermine.
Circular No. 23 of the Bureau of Standards recommends
that frogs be placed 10 to 12 feet back
from point of latch and held in horizontal position
by properly placing hangers on the line near frogs.
It has been the writer's experience that the distance
specified will be satisfactory for most of the
conditions encountered in mines.
Trolley frogs are provided, as a rule, with four
pull-off rings or eyes so that they may lie guyed
to the pioper position by the use ol' guy wires.
Never attach a guy wire on a frog or any other
trolley device which is to carry current, without
cutting in a Conical Strain Insulator in the guy,
which will properly insulate it.
Frogs should always be placed on branches leaving
main trolley.
Malleable iron trolley frogs are now making
their appearance upon the market and can be used
to advantage in mine service.
E. When dead-ending trolley wire, it should he
securely anchored and insulated, either by use of
a Conical Strain Insulator and ordinary turnbuckle,
or a Brooklyn Strain Insulator which is
really a combination of the above two mentioned,
or other suitable insulator. A suitable galvanized
clamp should be used for holding the dead-end loop
at the end of the trolley wire (see Fig. 4).
F. Allow proper clearances in all cases for the
trolley wheel. It is extremely bad practice to
allow the wdieel to touch the roof, even though the
roof may be hard sandstone or other formation, as
it increases wear on the wheel and is generally
unsatisfactory. It is better to install more hangers
where the trolley touches the roof; that is,
install them so that they will come closer together.
It is still better to shoot down a little of the top
and get the proper clearance, where conditions will
permit.
G. The manner of making the proper connection
at a point where feeder is to be tapped into the
trolley wire, should receive careful consideration.
The practice of hooking feeder around the trolley
clamps should not be permitted, as they invariably
work loose and cause trouble. A high resistance
will generate considerable heat and will produce
a very vicious arc which will probably burn off
the feeder. It is recommended that a good form
of feeder ear or clamp be employed, and where the
feeder is of such size that it will not fit the ear,
two or even three ears should be installed at that
point and suitable taps run from the feeder proper
to the ears (see Fig 5). The total area of copper
in circular mils in the taps should he equal to the
area in circular mils of the cable. Feed-in yokes
made especially for feeding in purposes may be
purchased in the market and will he found satis
factory for this purpose.
H. The selection of a proper trolley clamp is a
matter that should receive proper consideration.
Clamps have been designed which are too long and
which, when the hanger is installed slightly out
of plumb, produce a bump or projection in the
trolley wire which invariably causes arcing as the
trolley wheel passes the clamp (see Fig. 61. The
clamp should be narrow so that the wheel will
pass it without striking and the nut or other
clamping means should be located high enough on
the clamp proper so as not to strike a badly worn
trolley wdieel. A great deal of the sparking of
trolley at hanger points could be eliminated by the
use of a well designed clamp and keeping the hangers
carefully plumbed.
I. Splices in the electrical circuit should be
made with care, as it is astonishing to observe the
drop in voltage caused from poorly made joints.
Splices in the trolley circuit may be made by suit-