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either side of these are placed, in all, four shunt resistances for the dynamos. In the outer top corners are resistances for regulating the charging current of the accumulators, which, however, are only used when lighting is going on simultaneously with the charging. The various branch mains are taken off the top of the switchboard by means of safety plugs mounted above it upon slate slabs.

in their turn numerous complaints, loss of customers, and reduced profits. In many installations burn-outs both underground and in the station are frequent, with the natural result that the operating of circuits underground is not there considered an unqualified success. The writer has in mind two very different experiences with underground cables. Several miles of cable were bought by a certain company,

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Main Switchboard for High-Tension and Three-Wire Distribution, with Accumulators.

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carefully laid, and up to to-day not a single burn-out or interruption of service can be attributed to failure of cables; at about the same time another company bought about an equal amount of the same kind of cable, and in a comparatively short time the current had to be shut off the lines, and the whole installation repaired and parts of it replaced. Both of these experiences have been repeated many times, and will be again, although it is simply a distinction between a good cable properly laid and a good cable ruined by careless and incompetent workmanship.

Every failure can be traced to poor work in the original installation, or to the use of a cheap cable, both causes being due generally to that false economy which looks for too

quick returns. A poorly-insulated line wire and a poorlyinsulated cable are two very different things However, it is a fact that by the use of a good cable it is not difficult to construct an underground system for light, power, tele graph, or telephone uses that will be superior to overhead lines in its service and in cost of maintenance. The ideal underground system must have as a starting point a system of subways admitting of the easy drawing in and out of cables, and affording means of making subsidiary connections readily and with the minimum of expense and interruption of service. This is practically accomplished by a subway consisting of lines of pipe terminating at convenient intervals, say, at street intersections, in manholes, for convenience in jointing and in running out house connections. These pipes, or ducts as they are called, should be for two kinds of service; the lower or deeper laid lines for the main or trunk circuits, and a second series of ducts laid nearer the surface, running into service-boxes placed near together for lines to "house-to-house" connections. In some cities, where it is allowed to run overhead lines, the plan of running but one service connection in a block is followed, all customers in the block being supplied from a line run over the housetops or strung on the rear walls.

This makes unnecessary all subsidiary ducts except a short one from the manhole to the nearest building in the block, and effects a considerable saving in pipe, serviceboxes, cables, and labour. The manholes should have their walls built up of brick, the floors should be of concrete, and there should be an inside lid which can be fastened down and the manhole thus made watertight.

For ducts, wood, iron, or cement lined pipe may be used. To preserve the wood it is generally treated with creosote, which, in contact with the lead cover of the cable, sets up a chemical action, resulting in the destruction of the lead. Wood offers but little protection for the cable, as it is too easily damaged and broken through in the frequent street openings made by companies operating lines of pipe in the streets, and as one of the main purposes of a subway is that of a protection to cables, wooden ducts have little to recommend them except their cheapness.

Iron pipes are either laid in trenches filled in with earth, or are laid in cement. Iron pipe will, of course, rust out in time, and if absolute permanence in construction is desired, should be laid in cement, for after the pipe rusts out the duct of cement is still left. However, if we are going to the expense of laying in cement it would be much preferable to use cement-lined pipe, which is not only cheaper than iron pipe, but makes the most perfect cable conduit, as it affords a perfectly smooth surface to draw the cable over and give a good duct edge.

It is not necessary, however, in small installations of cable, especially where additional connections will not be of frequent occurrence, to go to the expense of subways, for cable may be safely laid in the ground in trenches filled in with earth, or can be enclosed in a plain wooden box or a wooden box filled with pitch.

There are, of course, many localities where, if the cable is laid in contact with the earth, a chemical action would take place which might result in the destruction of the cable. Underground cables are of the following classes: 1. Rubber-insulated cables, insulated with rubber or other homogeneous material. 2. Fibrous cables-so called from the conductors being covered with some fibrous material, as cotton or paper, which is saturated with the insulating material, paraffin, resin oil, or some special compound. Under this latter head is also included the dry core paper

cables.

The first thing to do is to get the cable drawn into the ducts, and on the proper accomplishment of this depends to a great extent the success or failure of the whole installation. Probably the ducts have been wired when the subway was constructed, but if not a wire must be run through as a means of pulling in the draw rope. There are several kinds of apparatus for getting a wire through a duct-rods, flexible tapes, mechanical " creepers," etc., but probably the best is the sectional rod. This simply consists of three or four foot lengths of hard wood rods, having metal tips that screw into each other. A rod is placed in a duct at a manhole, one screwed to that, both are pushed forward, another one added and pushed forward, and so on until they extend

the entire length of the duct. Then the wire is attached and the rods are pulled out and detached one at a time, and with the last rod the wire is through. At least No. 14 galvanised iron or steel wire should be used, for any smaller size cannot be used a second time, as a rule. In starting to pull in the draw rope a wire brush should be attached to the wire, and to this again the rope, and when the brush arrives at the distant end of the duct it very likely will bring with it a miscellaneous collection of material which for the good of the cable had better be in the manhole than in the duct.

The reel or drum carrying the cable should be mounted on wheels or jacks, and placed on the same side of the manhole as the duct into which the cable is to be drawn, and must always be so placed that the cable will run off the top of the reel.

There are several methods of attaching the draw rope to the cable. As simple and strong a method as any is to punch two or three holes through the cable, lead and all, and attach the rope by means of an iron wire-some of the draw wire will do-run through these holes. Depending on the length and weight of cable to be pulled, it can be drawn either by hand or by a multiplying winch. The rope should run through a block fastened in the manhole in such a position that the rope shall have a good straightaway lead from the mouth of the duct.

The strain on the cable should be perfectly uniform and steady. If the power is applied by a series of jerks, either the lead covering may be pulled apart or some of the conductors broken. At the reel there must always be a large enough number of men to turn it, and keep the cable from rubbing on anything, and in the manhole one or more men to see that the cable feeds into the duct straight and to guide it if necessary. If the ducts are of iron and are not perfectly smooth at the ends, these should be made so with a file, and in addition. a protector of some sort should be placed in the mouths of the duct, both above and below the cable. Six inches of lead pipe, split lengthwise and bent over at one end to prevent being drawn into the duct with the cable, makes a very good protector. The cable. should be reeled off the drum just fast enough to prevent any of the power used in pulling the cable through the duct being utilised in unreeling it. If this latter is allowed to occur the cable will be bent too short, and the lead covering buckled or broken, and also the cable may be jammed against the upper edge of the duct and perhaps cut through. If the reel is allowed to turn faster than the cable is drawn in the first three or four turns on the reel will slacken up, and the lead covering may either be dented or cut through by scraping on the ground. If the cable end when pulled through up to the block is not long enough to bend around the hole more than half way, the rope should be unfastened from its end, a length of rope with a wellfrayed out end should be run through the block, and by fastening to the cable close to the duct, with a series of half hitches as much slack as necessary can be pulled in. If this is properly manipulated there need not be a scratch on the cable, but unless great care is taken the lead may be pressed up into ridges and the core itself damaged. Immediately after the cable is drawn in, if the joint is not to be at once made, the open end or ends should be cut off and the cable soldered up, as most cables are very susceptible to moisture and readily absorb water even from the atmosphere. Where practicable it is always a good plan to pull the cable through as many manholes as possible without cutting the cable; for the joint is, especially in telephone or telegraph cables, the weak point. To do this the rope should be pulled through the proper duct in the next section without unfastening it from the cable; the winch should be moved to the next manhole, and pulling through, then done as before. There should always be a man in every hole through which the cable is running to see that it does not bind anywhere and to keep protectors around the cable. It is not advisable to pull more than one cable into a duct, and never advisable to pull a cable into a duct containing another cable, but if two or more cables have to go into the same duct they should always be drawn in together. Lead-covered cables and those with no lead on the outside should never be pulled into the same duct, for if they bind anywhere the soft cable will suffer where

two lead-covered cables would get through all right. Some manufacturers are now putting on their cables a tape or braid covering, which saves the lead many bad bruises and cuts, and is a valuable addition to a cable at very little additional expense.

Practically all electric light and power cables are either single or double conductors, and the jointing of these is comparatively a simple matter, although requiring considerable care. The lead is cut back from each end about 4in. or 5in., and the conductors bared of insulation for 2in. or 3in. The bare conductors should be thoroughly tinned by dipping in the metal-pot or pouring the metal solder over them. A sperm candle is better than resin or acid for any part of the operations where solder is used. A lead sleeve is here slipped back over the cable out of the way, and the ends of the conductors brought together in a copper sleeve, which is then sweated to a firm joint. This part must be as good a piece of work mechanically as electrically. The bare splice is then wrapped tightly with cotton or silk tape to a thickness slightly greater than that of the insulation of the cable, and is thoroughly saturated with the insulating compound until all moisture previously absorbed by the tape is driven off.

The lead sleeve is then brought over the splice and wiped to the cable. The joint is then filled with the insulating compound poured through holes in the top of the sleeve; these holes are then closed and the joint is complete, and there is no reason why, in light and power cables, that joint should not be as perfect as any other part of the cable. When the cable ends are prepared for jointing they should be hung up in such a position that they are in the same plane, both horizontal and vertically, and firmly secured there, so that when the lead sleeve is wiped on the conductor may be in its exact centre; and great care must be taken not to move the cables again until the sleeve is filled and the insulation sufficiently cooled to hold the conductor in position.

It is also very important to see that there are no sharp points on the conductors themselves, on the copper sleeve, on the edges of the lead covering or on the lead sleeve. All these should be made perfectly smooth, for points facilitate disruptive discharges. Branch joints had better be made as T-joints rather than as Y-joints, for they are better electrically and mechanically, although they occupy more room in the manholes. They are of course made in the same way as straight joints, a lead T-sleeve being used, however. For multiple arc circuits copper T-sleeves, and for series circuits copper L-sleeves are used.

Telephone and telegraph cables are made of any required gauge of wire, and with from one to 150 conductors in a cable. In jointing these the splices are never soldered, the conductors being joined either with a twist joint or with the so-called Western Union splice. Each splice is covered with a cotton or silk sleeve, or a wrapping of tape, the latter being preferable, although considerably increasing the time necessary for making the joint. Great care must be taken that no ends of wire are left sticking up, for they will surely work their way through the tape and grounds, and crosses will be the result. The wires should always be joined layer to layer and each splice very tightly taped in order to get as much insulated compound around each splice as possible in the limited space. The splices should be "broken" as much as possible, so as to avoid having adjoining splices coming over each other. After the joint has been saturated with insulating compound the wires should have an outside wrapping of tape to keep them in shape, and then the sleeve is wiped on and filled. If the insulation resistance of the jointed telegraph or telephone cable is a quarter of what the cable tested in the factory, it may be considered that an exceptionally good piece of work has been done. I have spoken more particularly of fibrous leadcovered cables, as the handling of them includes practically every step of the work on any other kind of under ground cable. In insulating dry core paper cables a paper sleeve is slipped over the splice, and in rubber cables the splice is wrapped with rubber tape; all other details are the same for these as for the fibrous cable.

In the laying of light and power cables every joint, as made, should be tested for insulation with a Thomson galvanometer, as the insulation must necessarily be very

high, and if one joint or section of cable is any weaker than another it may be very important in the future to know it. All tests must be made after the joint has cooled, for while hot its insulation resistance will be very low. Tests for copper resistance should also be made to determine if the splices are electrically perfect; an imperfect splice may cause considerable trouble. In telegraph and telephone cables the conductors should be of very soft copper, for in stripping the conductor of insulation it is very easy to nick the wire, and if of hard drawn copper open wires will be the result.

All work should be frequently tested for continuity with telephones, magnetos, or small portable galvanometers. It is only necessary to ground the conductors at one end and try each wire at the other end. For this sort of work a telephone receiver used with one cell of some dry battery is most convenient, and has the additional advantage of affording a means of communication while testing, and is by far the best thing for identifying and tagging conductors. These cables should be frequently tested during the progress of the work for grounds and crosses with a Thomson instrument, and when the cable is complete a careful series of tests of the capacity, insulation resistance, and copper resistance of each wire should be made and the exact condition of the cable determined before it is put in service, and thereafter an intelligent oversight of the condition of the circuits can thus be more readily maintained.

Where a company has extensive underground service, a regular cable gang should be in its employ, for quick and safe handling of cables demands the employment of men accustomed to the work. If the cable has been properly laid, and tests show it to be in good condition before current is turned on, almost the only trouble to be anticipated will be due to mechanical injury. Disruptive discharge, puncturing the lead, may occur; but the small chance of its occurring can be greatly lessened by the use of some kind of "cable protector," which will provide for the spark an artificial path of less resistance than the dielectric of the condenser, which the cable, in fact, becomes.

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If a fault suddenly develops on a circuit, the chances are it will be found in a manhole, and an inspection of the cable in the manhole will generally reveal the trouble without resorting to locating with a Wheatstone bridge. The cable is often cut through at the edge of the duct, or damaged by something falling on it, or by someone walking all over it." To guard against these, the ducts should always be fitted with protectors both above and below the cable. The cables should never be left across the manholes, for they then answer the purpose of a ladder, but should be bent around the walls of the hole and securely fastened with lead straps, that they may not be moved and the lead gradually worn through.

In telegraph cables, when one or two conductors " 'go," it will probably be useless to look for trouble except with instruments; but if several wires are "lost" at once it will probably be found to be caused by mechanical injury, which can be located by inspection. If it is ever necessary to loop out conductors, a joint can be readily opened and the conductors wanted picked out and connected into the branch cable and the joint again closed without disturbing the working wires. In doing this a split sleeve must be used, and the only additional precaution to be taken is in filling the sleeve to have the insulating compound not hot enough to melt the solder and open up the split in the sleeve. In cutting in service on light and power cables it is entirely practicable to do so without interruption of service on multiple-arc circuits, even those of very high voltage; but they require great precaution and involve considerable risk to the jointer, and where possible the circuit to which the connection is to be made should previously be cut dead. Where the voltage is not dangerous to human life, almost any service connection can be made without interruption of service.

I have only indicated a very few of the operations that may be found necessary, and the probable causes of troubles that may be encountered in the operating of underground circuits, believing that the different problems that arise can with a little experience be successfully met by anyone who has a fair knowledge of the original construction of cable lines.-Electrical World (N.Y.).

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TELEPHONY IN LONDON.

The excellent and suggestive paper of Mr. Bennett at the British Association has given rise to a general discussion on telephony and also to a special discussion on telephony, as it is proposed to deal with it in London. The Duke of Marlborough, Mr. Campbell-Swinton, and others have entered with some warmth into this discussion, advocating competition with the company already in the field. So far as we are concerned, we shall assist such competition by every means in our power. Having stated this determination, it may be perhaps thought by readers that some reason for it should be given.

are

all

It is but just to give some reason, for we cricket umpire neither in the position of a nor a judge, both of whom have been advised to give decisions but no reasons. From the users' point of view telephony in London is far too expensive, the service is bad, and the cross-talk makes it possible to hear that which you wish not to hear, and to hear doubtfully and painfully that which you desire to hear. As Prof. Kennedy put it in the Times of Wednesday, "That the existing telephone service in London is hopelessly unsatisfactory, is but too well known to all of us who have to use it, or—as is much more commonly my own case— to try to use it." For years the management of the present telephonic system was purely financial, and though a gigantic effort has been made since the change of management to cope with the legacy of difficulties, Hercules himself could not satisfactorily perform the task. This much from the users' point of view. If we ask what the existing telephone monopoly has done towards progress, one looks in vain through the files of the technical papers issued during its existence and finds nothing. Edinburgh, Newcastle, Manchester, Bristol, and Brighton have contributed to 13s. Od. extend our knowledge of the subject both theoretically and practically, but London, both in its applications and its manufacture, has been like an empty safe with the door shut and the key lost. Sounded from the outside it seems filled with emptiness, though when merely looked at it makes an imposing spectacle. The sooner the end comes to such monopoly the better. The best instruments come from Antwerp and Berlin. The switchboards are almost entirely of American origin. Some of the correspondents have been quarrelling over the huge capital of the National Company, and insisting that with proper financial administration and less watering, the rental might well be halved and as good a dividend paid. The people who argue in this strain forget that it pays financialists and promoters better to look after their look after the interests of bona fide investors through own interests while they have the chance, than to look after the interests of bonâ fide investors through a longer period. Promotions, amalgamations, concessions, family companies and compacts, reorganisations, every move means plums to the skilful wire puller-and who shall say him nay? Not those who benefit with him, not those who buy and sell shares

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at a profit, not those who get satisfactory dividends: only those who see the way to do a little business themselves. Depend upon it, pure philanthropy plays no part in business projects, and the fewer stones thrown at one set of promoters to curry favour with another set the better. So far as the project enunciated by the Duke of Marlborough is concerned, no doubt it is a purely business project, initiated because money can be made thereby, for which those who promote it have to thank the existing company. The public wants a better and a cheaper service, and, if this can be given, will support those who give it. The system proposed by the Duke of Marlborough and his coadjutors is undoubtedly the best system at present known, and the best system so far as scientific knowledge can foresee. No earth, most wires underground, proper instruments, organisation, and a good service at a low rate ought to bring the telephone into almost or quite every house. From the point of view that assumes the majority of houses fitted, a £10 rental would be a maximum charge; and if users could be brought to co-operate, say, by renting at £9 to every shareholder subscribing to the capital of the company to the extent of £5, while the rental was £10 to every householder not a shareholder, a goodly number of £5 shares would be taken, as the shareholder would get a direct 20 per cent. incentive besides his other advantages; or if this is too much, give him a 10 per cent. by making his stake in the company £10 instead of £5-in other words, appeal to his pocket to support the better scheme.

LOAD FACTOR.

lamps that savour of luxury rather than of necessity. The dining-room and the drawing-room—a few of the best rooms of the house in most cases, in less cases the servants' rooms, the cellars and offices so far as residential districts are concerned-in business houses the shops or salerooms, and not the back, living, or work rooms; in fact, in all those places where show and not use is paramount. From the conditions of the case the demand would fluctuate within wide limits, for almost all these spaces require the light about the same time. If, however, the light is more generally adopted, as it undoubtedly will be, the load diagram will have a different contour, and the load factor obtained from a study of load diagrams in the early days will mislead, and plant designed and arranged to suit this load factor will not be so well designed and arranged as plant designed in view of obtaining a different. load factor. Then again a study of load factor will probably bring practical men to select areas for work which are of a mixed character-that is, partly business and partly residential. A station having, say, an equal number of lamps wired in shops and in dwelling-houses, finds the curve of the diagram rising sooner and continuing high longer than one with lamps wired solely in dwelling-houses. The addition of factories and workshops again alters the character of the curve, especially in the morning hours. With such a mixed demand the curve becomes flatter. The maximum demand at one time is but little increased, because the demand in factories and workshops is not made at the same time as that of salerooms and dwelling-houses. It is from such reasoning as this that we suggest the natural course of things will be to give better

now existing.

THE NEW SHORT RAILWAY GENERATOR.

The publication of Mr. Crompton's paper by the diagrams rather than to accentuate the peculiarities Institution of Civil Engineers will call attention once more to the various practical points discussed at the reading of the paper last April. Mr. Crompton is nothing if not practical. Most electrical engineers recollect how he shocked the dry-as-dust bookmen when he took credit of being able to arrive at certain decisions by means of his "eye." It seems to be forgotten that in no one branch is engineering an exact science, hence we make bold to assume that too much attention may be given to the load factor. Mr. Crompton, in his paper, assumes that because we have obtained a certain number of load diagrams we are able to foretell the load factor of any similar district, and implies

that a

somewhat implicit trust must be put upon the load diagrams now obtained. We incline to the opinion that almost all load diagrams hitherto obtained are misleading, and in the future load diagrams in the same stations will differ considerably from those of the present. Even if work is restricted almost entirely to the supply of the demand for electric lighting, there will come a considerable eration in the load diagrams. Our reason for this rmise may be briefly stated. be briefly stated. In the earlier days of central station work-and these are early daysby far the larger proportion of the lamps wired are

It is an event well worthy of notice when one of the large electric railway manufacturing companies puts upon particularly true when to general novelty in design are the market an entirely new type of generator. This is added principles of construction which are so evidently well adapted to their purpose that the advance upon former methods is at once evident even to the uninitiated. The Short Electric Railway Company has just brought out the first of a series of railway dynamos which are admirable in every respect. They are massive in form, simple in construction, and are marked by the mechanical perfection and finish for which the Short Company is

noted.

The illustration gives an excellent idea of the 150-h.p. generator, capable of delivering in continuous service 225 amperes at a pressure of 500 volts, equivalent to a total electrical output of 112,500 watts, and having, in fact, a reserve capacity above the normal of at least 30 per cent. in both current and voltage.

The field magnet frame is one of the largest and most

perfect single castings ever made for electric work. It

weighs over 8,000lb., and nothing but the softest and
purest iron is used in the melting-pots. It is annealed
very slowly in the moulds, and when finished it is so soft
a hammer. For
that it can easily be indented with
a monster planing machine, one of the largest to be
properly finishing up this casting it was necessary to build
obtained.

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