February 21, 1913. THE COLLIERY GUARDIAN. 399 ELECTRIC CABLES IN MINES.* By Gr. W. T. Anderson, M.Inst.M.E., M.I.E.E. (Continued from page 332.) Roadway Cables. For choice, intake airways should be selected, and the position chosen for the run should be such as to afford the greatest security from mechanical damage. In main roadways where there are good walls and sound roofs, the cables may be fixed in a permanent manner by cleats. Where there is a liability of damage from falls, the cables should be suspended in such a manner and with so much slack that they will readily tear away without fracture. With this in view, many methods of slinging are adopted—the least reliable being, perhaps, the pig skin suspender, in which the eyelet is very prone to draw out as the material deteriorates. Better far is the simple expedient of tarred marline fixed at regular intervals not exceeding say, 10 ft. A type frequently used is a modification of the heavy sling previously described, fitted with a galvanised wire hook so proportioned that, whilst remaining intact under the normal weight of the particular cable borne, it will readily draw out under the strain of a fall. Roadway cables more than any others are liable to come under Section C of Rule 12, and it may be mentioned that single armoured cables (under certain normal conditions enumerated), will require to have their sheathings bonded together every 100 ft. Also that if two singles are so used the conductivity of the sheathings of either shall be at least equal to 25 per cent, of the conductivity of the conductor enclosed thereby. For installing, it is advisable to take the new roadway cable down the pit intact on its drum, jacking it up on an improvised trolley running on tub wheels, and paying out as the trolley moves along. If there is not room for the drum to be taken down the road it must be jacked up and the cable drawn off and run inbye on tubs, rollers or pit props, care being taken to avoid dragging it along the ground and so causing needless abrasion to the outer servings of jute. If it is found impossible to get the drum down the shaft, the cable can be taken off at bank and lowered— either lashed to a haulage rope or fixed to a capel—and run inbye as it descends. Under no circumstances should a twist or kink be allowed to occur. This brings one to the question of Boxes. Boxes, the importance of which cannot be over- estimated, not only as seals to prevent moisture entering the dielectric, but as means for making off the armour in an electrically and mechanically sound manner, and of thus effecting continuity of the sheathings. None but trained jointers should be employed on this type of work, and only the very best materials put in. If the sweating of cores cannot be undertaken for reasons of general safety, mechanical connectors, having an electrical conductivity not less than that of a sweated joint, should be used, care being taken to so protect such fittings with tape that the hot compound cannot creep into their crevices with the possibility of ultimate sparking. The fundamental features to be looked for in joint boxes are:— 1. Absolute watertightness and mechanical strength. 2. Long bearing glands, which will prevent any undue strain being put upon the cable or the internal fittings of the box, while they are capable of making a very effective connection with metallic sheathings. 3. Adequate means of bonding through from sheathing to sheathing. 4. Such design as will reduce to a minimum the risk of cavities or “ blowholes ” forming in the compound. In a solid box or disconnecting box of any size it is advisable that all pedestals rest on porcelain feet (immersed in the compound). Other materials for mounting studs—such as impregnated hard wood or fibre mouldings—are liable to be treacherous. Much the best method of arranging shaft joints is to make a horizontal connection in a heading or inset, even at the expense of such an inset having to be specially constructed. The most suitable box for this work is undoubtedly that of horizontal type, in which the incoming and outgoing cables enter at one end. When it is desired to feed various levels from the shaft cable, a similar type of horizontal box may be used with an additional gland at its inner, or roadway, end. As regards terminal boxes, certain courses are necessary to comply with the new rules. Such boxes are usually of the bifurcating or trifurcating type, and * From a paper read before the Manchester Geological < and Mining Society. the question of protection of leads between box and switchboard, or between controllers and haulage motors, is one of some difficulty. When, for reasons of electrical efficiency, they must be under one cover, the writer is inclined to think a wrought iron case constructed on site is, perhaps, the most suitable method to adopt. Alternatively, a box may be provided specially designed for use in any position, fitted with stuffing glands and screwed so that barrelling, large enough to enclose three V.I.R. singles, can be fixed to the box. Such design is shown in the illustration (fig. 5). Compounding. When joints are completed, the box must be filled up with an insulating compound to protect conductors and insulation from moisture. For mining work the writer has always made it a custom only to use compounds suitable for E.H.T. work, preferably with a high melting- point, having a pouring temperature of, say, 300 degs. to 330 degs. Fahr. Fig. 5. i (o While overheating is injurious to the compound, it should never be used too cold, as the efficacy of the seal is thereby endangered. Not only should the correct pouring temperatures of any compound be ascertained, but jointers should always be made to use thermometers to gauge such temperatures. Where heating cannot be Table 4u.—Results showing Percentage Lost by Coal when Dried in Water Oven for Periods Stated. Worker. Grammes of coal. Time of heating. Coal Number. 1. 2. 3. 4. 5. 6. Hours. 7’10 2’90 9’70 7T0 5’30 7’20 I. ) l2 i 270 9’60 6*80 5’30 6’90 7’10 1 ] li I 2 j 2’80 9’70 7T0 5’30 6’80 7’10 2'70 9-70 7’10 5 30 6’80 7’30 VIII. 1(W.B.) 1 ! 3'12 9*76 7’30 5’50 7’00 7’48 IX* 4 2*90 9’69 7’36 5’40 7’06 7’38 XII. XVI. £ 1 1 3 12 9-78 7’28 5’46 7’31 7’66 5 (In dishes till constant weight) 2-86 9’42 7’08 5’25 6 72 6’95 2 (Watch glasses until constant) 2’90 9’48 7’12 5’27 6 35 7’07 Maximum 312 9’78 7’3^ 5 50 7*31 7’66 Minimum 2*70 9*42 6’80 5 25 6’72 6’95 Average 2-89 9’65 7’14 5’34 6’96 7’25 * See 2. done locally, it is necessary to get the compound rapidly transmitted from bank to box in some non-conducting jacket arrangement on the thermos principle; and in a somewhat wide experience the writer has seldom found much difficulty in effecting this, generally by such simple process as placing large buckets in tubs filled with sawdust or some similar material. The compound should be poured rapidly and con- tinuously into the box, preferably through a funnel, and every facility should be given for air and gases to escape. It is essential that the boxes should be so efficiently filled that no cavities are left. If, on inspec- tion after cooling, the box is found to be not quite full, final toppings are absolutely necessary. Earthing, As regards bonding and earthing, the new rules really enforce what manufacturers have been making their standard practice and generally recommending for years past. Copper plates should be avoided, on account of their rapid deterioration. Iron cylinders or pipes driven vertically into the ground and filled with breeze, into which engine cocks can drip, make perhaps the best job, provided a sound (and visible) mechanical and electrical connection is made with them. Alternatively, a couple of old boiler plates thrown into a pond have often been known to give excellent results. It is always well however, in addition to any earth plates at the surface, to bond all metallic sheathings (by means of three or four separate tinned copper conductors made off with lugs) to the flanges of pipes,.known always to contain water, and which form a widely distributed contact with the main mass of earth. In conclusion, the writer would put forward an earnest plea in respect to upkeep and maintenance. Nearly all the faults met with in his experience—barring those of a purely mechanical nature—have been due to careless- ness, and were readily preventable. Rigid tests for insulation resistance, for continuity of sheathings and for proving the efficiency of earth connections, should be made in respect to all cables at least once a month, and their results recorded and compared. Deterioration, or even the result of unknown mechanical damage, may thus be traced before serious consequences follow. THE DETERMINATION OF WATER IN COAL. (Continued from page 329.) SECTION 4. Methods of determining water other than those indi- cated in the president’s circular letter of October and included in the preceding sections. (a) Drying in a water oven. (5) Drying in a current of inert gas. ( —) Indirect determinations—loss of weight of coal. ( + ) Direct determinations—gain of weight of drying tube. (c) Drying for J hour at 105 degs. of varying weights of coal spread over varying surfaces. (d) Drying at 105 degs. for varying times (J hour to 2 hours). (e) Drying in desiccators at ordinary pressure. (/) Expulsion of water by boiling coal with xylene and measuring the volume of water evolved. 4a.—Several workers have made series of experiments in which coal is dried in the water oven. The results are given in Table 4a. It will be noticed that the figures, on the whole, agree more closely than those obtained by drying at a higher temperature or in a vacuum. They are, however, in all cases but the maxima obtained on 1 1 and 3, lower than the average results obtained by drying at 104-107 degrees or by drying in a vacuum. It seems clear that either (1) the temperature reached in a water oven is insufficient to drive off all the moisture, except perhaps in a carefully dried atmosphere, or more probably (2) owing to the slow rate of drying the gain of weight due to oxidation seriously diminishes the loss of water. An exploration by the vice-president of a large water oven 22 5 cm. x 25’5 cm. x 32’5 cm. by means of a thermo couple showed that the temperature varied considerably in different parts, temperatures as low as 16 degs. below that of steam having been recorded. The effect of opening the large door (22’5 cm., 25’5 cm.) was very marked, since the thermo couple, which has no appre- ciable lag, did not attain a stationary temperature for some minutes after each opening. It was noticed that, although the door was by no means airtight, the closing of the little damper in the door raised the temperature about 0’7 deg. even on the bottom of the bath at the back. Experiments by Messrs. Andrews, Coste and Powney on a very moist coal examined by them seem to show that at a temperature below 100 degs. the loss of water is so much less rapid than at 105 degs. that a true figure for moisture cannot be obtained within a reasonable time, although the heating be continued over some hours in an inert atmosphere. The uncertainty as to the temperature in a large water oven, although (judging from the small differences between the loss in one hour at 79 degs. and a reputed