February 13, 1914.

THE COLLIERY GUARDIAN.

351

MIDLAND COUNTIES INSTITUTION OF
ENGINEERS.

Meeting at Nottingham.

A general meeting of the Midland Counties Institu-
tion of Engineers was held last Saturday at University
College, Nottingham. Mr. W. H. Hepplewhite,
H.M. inspector of mines, presided.

Mr. G-. A. Lewis announced that the following had
been elected by ballot:—Members : Edward Cousens,
mining engineer, c/o Harding Brothers, Broadway-court,
Westminster, S.W. ; John George Jones, colliery
manager, Whitwell Colliery, Whitwell, near Mansfield,
Notts; Robert Edmund Martin, M.A., Mountsorrel
Granite Quarries,Loughborough; Henry Atwell Purdon,
civil engineer, 10, Lower Grosvenor-place, London, S.W.;
James Toman, mining engineer, Sutter Creek, Amador
County, California, U.S.A. Associate: John Ball,
under-manager, High Park, Newthorpe, Notts ; Student:
Edward Emerson Melly, B.A., student, Wath-upon-
Dearne, Rotherham.

Shaft Pillars.

A paper by Mr. Charles Snow, on the “ Removal of
a Shaft Pillar at Kirkby Colliery,” was discussed in
combination with the paper entitled “ Why Leave Shaft
Pillars,” by the late Mr. W. H. and Mr. Basil H.
Pickering.

Mr. J. Mein (South Norman ton) thought that the
question of the removal of shaft pillars was a purely
academic one, and not one which could be said to come
within the range of practical politics. Where would
they find a mining engineer who, after sinking a shaft
600 to 700 yards in depth, would dare to begin to get coal
immediately he reached the bottom. If the experiment
proved a failure he would get all the kicks.

Mr. T. G. Lees (Newstead) said that it was promised
that the shaft pillar at Brods worth—where the shaft
was 900 yards deep—would be removed. As a matter
of fact, it had not been removed, and it would be
interesting to know why Sir Arthur Markham had
altered his mind.

The President, after remarking that Mr. Snow was
not present at that meeting, suggested that the shaft
pillar at Kirkby might have been too small, and that it
had begun to “ creep.” Probably in such a case it would
be better to remove it. He was recently down a W ar wick-
shire mine, where an enormous quantity of water had to
be dealt with. They had gone to very great expense in
putting in cribs and special tubbing, with the result
that the shaft was now in spick-and-span order. Were
they now to begin to get the coal at the bottom of the
shaft they would set the latter all “on the go” again.
He agreed with Mr. Mein that it was a risky thing to
remove the shaft pillar, and that it would be rash to
attempt it.

Mr. R. Laverick (Nottingham) said that they ought
not to overlook the fact that the actual thing had been
done at a particular colliery—the shaft pillar had been
removed at Kirkby. He should like to know what the
effects had been. Had the tubbing in the shaft been
disturbed at all ? In a case where there was tubbing
holding back a large quantity of water, it seemed a rash
thing to take away the shaft pillar.

Mr. E. E. Bramall (Leicester) said that if a mine
were liable to spontaneous combustion, and there was a
risk of fire at the back of the shaft walling, he could
understand that it might be advisable to remove the
coal and resort to hydraulic stowage, but such a case
seemed to be the only one where the removal of the
shaft pillar would be warranted.

Mr. G. A. Lewis (Derby) pointed out that the paper
itself answered one of two of the points which had been
raised. Mr. Snow distinctly said that the tubbing in
the shaft had not been affected in the slightest degree
by the coal being taken out. According to the paper,
the shaft at Kirkby was 700 yards deep, and 15 ft. in
diameter. The shafts were tubbed to a depth of 360 ft.
The seam was 3 ft. 9 in. thick, and had an inclination of
1 in 18 to the north.

Mr. F. Chambers (Heath) remarked that Mr. Snow
had not told them if the shaft pillar had been robbed
before he went there; and if so, to what extent. It was,
however, very different to clear out the shaft pillar of
an old shaft from starting at the bottom of a new one
and removing the coal.

Electricity.

A short discussion then took place on Mr. Robert
Nelson’s paper (addressed to colliery managers) on
“ Electricity.”

The President referred to a case of electrocution in
a Warwickshire mine. Some work was being done on
a cable and the current was shut off, but the rule
requiring the handle to be removed from the nearest
circuit-breaker was not observed. When the next shift
came on there was some bungling with regard to the
signals, and the handle being in position the current
was turned on, with the result that the man at work on

the cable received 580 volts. There was no doubt that
when any work was being done to the cable in-bye of the
last circuit-breaker, the man should take the handle
with him. He should not trust himself to any human
factor, or to signals.

Mr. W. C. Phillips (Ansley) said that he knew the
colliery to which the president had referred, and it was
a rule there for the electrician, when he was going to do
anything with the cable, to remove the handle from the
switch and take it with him. If that had been done in
this case the accident would not have happened, and the
neglect of the rule cost a man’s life. It was easy, when
there were as many as 20 beats for one signal, for a
mistake to be made, but a district ought to be in the
hands of the man doing the cable work, and it would be
entirely in his hands if he put the switch-handle in his
pocket.

Mr. Mein, touching on the subject of the “human
factor,” related an incident which occurred at his
colliery. He was going round a district one day, and
found a coal-cutter standing, and the three men in
charge taking their ease. On enquiring why the coal-
cutter was not working, the men replied that they were
waiting for the current. His under-manager was with
him, and he asked, “ Have you switched it on ? ” It turned
out that they had not! The men were paid by piece, so
that they had no interest in resting.

Mr. W. Beckett observed that where a mine was
not very extensive, the last circuit-breaker might be in
the switch-house. In such cases the switch-house
should always be under the absolute control of compe-
tent men, and when work was being done on the cable
a board notifying the fact in bold letters should be
placed over the handle. At the colliery with which he
was connected, the switches where the circuit was
broken were in places which were locked up so that only
authorised persons could gain access. A board placed
over the handle warned any of those authorised persons
who entered the place that work was being done to the
cable. He did not care so much for the idea of a
removable handle, because a man might have in his
possession a handle belonging to somewhere else, or a
spare handle, and be tempted to shove that in.

Before the meeting closed, Mr. Phillips made an
earnest appeal to the students of the institution to
contribute papers. Certificated managers of collieries
were at present overcrowded with statutory duties, and
had little time for sleep, to say nothing of preparing
papers for that institution. He would like some of the
prizes which were offered by past presidents for com-
petition to be specially allocated to students, and he
could assure them that there would be no hypercriticism
on the part of the older members, but that they would
be treated in the discussions with all the generosity
which ought to be extended to them under such circum-
stances. It was rather infra dig. that they had nothing
to discuss that day except papers read before other
institutions, and he trusted that some effort would be
made, especially by students, to alter such a condition
of things.

This concluded the meeting.

HORTH STAFFORDSHIRE INSTITUTE OF
MIKIKG AHD MECHANICAL ENGINEERS.

Electricity for Mine Managers.

{Continued from page 314).

At a meeting of this institute, held at Stoke last week,
Mr. Hugh Johnstone presiding, Mr. Robert Nelson
read a paper entitled “ Electricity : the Continuation of
a Recent Paper Addressed to Colliery Managers.” We
give below a report of the discussion.

The President, in inviting discussion, said they had
had a paper of great practical value—one that teemed
with commonsense, and one that was of intense interest
to the members of the institute, as was evidenced by the
large attendance.

Mr. John Gregory observed that the general tone
of the paper was that, with the apparatus at present in
use, three-phase working had decided advantages
over continuous current. Probably, with the exception
of Mr. Nelson himself, he (Mr. Gregory) had had a
longer experience in three-phase working than anyone
else in the room, and he was in perfect accord with him
in the view he took. There was no doubt that the
advantage of the squirrel-cage motor could not be
over-estimated. Unfortunately, it had its weak points,
inasmuch as they could not very well have a speed regula-
tion with it, and for any work such as haulage, where the
load had to be started up slowly, the slip-ring motor had
been almost essential. Lately he had been going into the
question of using squirrel-cage motors for such work,
and was intending shortly to make a trial of epicyclic
gearing. By means of that the load could be taken up
much more gradually than with most types of friction
clutches. There was one point upon which he did not
see eye to eye with Mr. Nelson, and that was earthing
the neutral point on a three-phase system. If an
automatic contrivance for cutting off the current
immediately a -leakage exceeded a predetermined
amount were essential, it was not necessary that the
neutral point should be earthed. With regard to Mr.
Nelson’s remarks on the attention to be paid to the
making of cable joints and the joining in of cables to

apparatus, he was pleased to say that the best makers
of motors and controlling apparatus for mines were
paying great attention to this point, and several firms
offered apparatus which was almost perfect. For
many years now it had been the practice to lead the
armoured cable up to the controlling switches ; but
there had been some laxity in the disposal of the cable
between the controller and the resistances. Some of
the makers had arranged pipe connections, so that all
the cables could be totally enclosed. Mr. Nelson spoke
of the advisability of telephone and signalling wires
being armoured in a similar manner to that adopted for
the larger cables carrying heavier current. A little
difficulty appeared to suggest itself with regard to
signalling wires. In the past the general custom had
been to run bare wires in order that a signal might be
given from any point of a long roadway. One or two
makers were trying to overcome that difficulty by run-
ning insulated wires with pushes at, say, 200 yards
intervals, and connecting to all the pushes a length of
signal wire, so that signals could be given in the same
way as if the signalling were mechanical. He
agreed with Mr. Nelson that if the difficulties could be
got over it would be an advantage for signal and
telephone wires to be armoured.

Mr. W. T. Anderson said Mr. Nelson’s advocacy of
the three-phase system was very wise. He had a case
recently where there was a loss on a 500-volt D.C. circuit
of no less than 120 volts between generator and machine;
and f they realised that to halve that loss they had to
double their copper area, they got an idea of what direct
current meant. He had another case in a colliery
where the face was so far from the direct current
haulage that they were putting in alternating current to
draw coal as far as the furthermost limit of the direct
current haulage. He could have wished that Mr.
Nelson had said more about jointing. There was no
doubt at all that the metallic armouring should be
without break from the generating station to, at least,
the gate end box, and it was probable that in this
connection few joints could be found underground at
the present time over which the metallic sheathing
complied with the law in regard to its relative conduc-
tivity with the conductor. On the subject of earthing,
Mr. Anderson said the buried earth plate was seldom any
good and it gave a false sense of security. He thought
the conditions laid down by Mr. Trotter for tramway
systems should be rigidly enforced at every colliery.
These consisted of earth plates, not less than 20 yards
apart, on which periodic tests had to be made. That
was the only way to obtain an idea of what sort of
contact they were getting with the general mass of earth.

Mr. J. F. Aust said he quite agreed with Mr. Gregory
as to the earthing of the neutral point.

Mr. J. R. L. Allott said that personally he preferred
to have a completely insulated system, rather than one
with the earthed neutral. Perhaps it was because, if
anything happened to one phase, he could keep going
whereas if the neutral were earthed he should have to
stop the pit while it was put right. His idea was that
they could maintain a high standard of efficiency and
protection if they took careful tests and looked well
after the insulation and the jointing. He asked Mr.
Nelson to explain the device which, with the earthed
neutral, would come into operation in the event of a
leakage.

Mr. E. B. Wain said 15 years ago, when alternating
current was more or less on its trial, quite a number of
collieries in North Staffordshire adopted continuous
current, and, so far, he did not think they had found any
real cause for regret. One important point was that a
very large proportion of the work was heavy haulage
work. Personally, he had in use something like 1,500-
horse power of continuous current, working at distances
up to 1 mile or more from the shaft, although he was
bound to admit that the point had been reached beyond
which it would not be economical to take continuous
current. Up to that limit it had been everything that
could be desired. Further, he believed the older motors
that were built 12 or 15 years ago were more capable of
heavy duty and heavy overload than the motors of
to-day. He should like to ask Mr. Nelson’s opinion on
a mixed system—how far it would be possible or politic
to couple up an existing continuous-current plant with
three-phase generation. Three-phase generation was
undoubtedly the most adaptable for high-speed
machinery.

Mr. Gregory, on the subject of earth plates, said
there were in the district a number of cases where
multiple earth plates were used and tested, and he
thought they had to thank the previous paper of Mr.
Nelson for drawing attention to the very point Mr.
Anderson raised.

Mr. W. J. Bates, having had experience of both
continuous current and alternating current, spoke in
favour of the latter. There was no doubt that
alternating current had a great advantage for heavy
work and for centrifugal pumps. Squirrel-cage motors
were essential for pumping, but they had a disadvantage
when used for intermittent work in haulage. With small
motors that could be overcome with friction clutches.

Mr. Anderson, reverting to the question of earth
plates, said the use of copper earth plates was a positive
danger. He knew a case in which 60 copper plates, of
six superficial feet each, were put in, and there was
nothing left of them in 12 months. They rapidly
deteriorated from electro-chemical action.