Fig. 73.Fig. 73.
Fig. 73.
§ 68. Whenever possible, the wiring of a house, etc., for bell work, should be done as soon as the walls are up and the roof is on. The shortest and straightest convenient route from bell to battery, etc., should always be chosen where practicable to facilitate drawing the wire through and to avoid the loss of current which the resistance of long lengths of wire inevitably entails. The wires should be run in light zinc tubes nailed to the wall.
Fig. 74.Fig. 74.
Fig. 74.
In joining up several lengths of tubing, the end of one piece of tube should be opened outconsiderablyof a trumpet shape for the other piece to slip in; and the end of this latter should also beslightlyopened out, so as not to catch in the covering of any wire drawn through it. The greatest care must be exercised in drawing the wires through the tubes or otherwise, that the covering be not abraded, or else leakage at this point may take place. In cases where tubes already exist, as in replacing old crank bells by the electric bells, the new wires can be drawn through the tubes, by tying the ends of the new wire to the old wire, and carefully pulling this out, when it brings the new wire with it. Or if the tubes are already empty, some straight stout wire may be run through the tubes, to which the newwires may be attached, and then drawn through, using, of course, every possible precaution to avoid the abrasion of the insulating covering of the wire, which would surely entail leakage and loss of current. All the old fittings, cranks, levers, etc., must be removed, and the holes left, carefully filled with dowels or plaster. In those cases where it is quite impossible to lay the wires in zinc or wooden tubes (as in putting up wires in furnished rooms already papered, etc.), the wires may be run along the walls, and suspended by staples driven in the least noticeable places; but in no case should the two wires (go and return) lie under the same staple, for fear of a short circuit. It must be borne in mind that each complete circuit will require at least two wires, viz., the one leading from the battery to the bell, and the other back from the bell to the battery; and these until connection is made between them by means of the "contact" (pull, push, or key) must be perfectly insulated from each other. In these cases, as far as possible, the wires should be laid in slots cut in the joists under the floor boards, or, better still, as tending to weaken the joists less, small holes may be bored in the joists and the wires passed through them; or again, the wires may be led along the skirting board, along the side of the doorpost, etc., and when the sight of the wires is objectionable, covered with a light ornamental wood casing. When the wires have been laid and the position of the "pushes," etc., decided upon, theblocksto which these are to be fastened must be bedded in the plaster. These blocks may be either square or circularpieces of elm, about 3 inches across, and 1 inch thick, bevelled off smaller above, so as to be easily and firmly set in the plaster. They may be fastened to the brickwork by two or three brads, at such a height to lie level with the finished plaster. There must of course be a hole in the centre of the block, through which the wires can pass to the push. When the block has been fixed in place, the zinc tube, if it does not come quite up to the block, should have its orifice stopped with a little paper, to prevent any plaster, etc., getting into the tube. A little care in setting the block will avoid the necessity of this makeshift. A long nail or screw driven into the block will serve to mark its place, and save time in hunting for it after the plastering has been done. When the blocks have been put in their places, and the plastering, papering, etc., done, the wires are drawn through the bottom hole of the push (after the lid or cover has been taken off),Fig. 74, and a very small piece of the covering of the wire having been removed from each wire, and brightened by sand papering, one piece is passed round the shank of the screw connected with the lower spring, shown to therightinFig. 74, and the other round the shank of the screw connected to the upper spring, shown to theleftin the Fig. The screws must be loosened to enable the operator to pass the wire under their heads. The screws must then be tightened up to clench the wire quite firmly. In doing this, we must guard against threethings. Firstly, in pulling the wire through the block, not to pull so tightly as to cut the covering against the edge of the zinc tube. Secondly, not to uncover too much of the wire, so as to make contact between the wires themselves either at the back of the push, or at any other part of the push itself. Thirdly, to secure good contact under the screws, by having the ends of the wires quite clean, and tightly screwed down.
§ 69. In all cases where the wires have to be taken out of doors, such as is necessitated by communication from house to outhouses, stables, greenhouses, etc., over head lines (No. 18 gauge, gutta-percha tape and tar covering) should be used. Where overhead lines are not admissible, either as being eyesores, or otherwise, the wires may be laid in square wooden casings of this section┗━┛, the open part of which must be covered by a strip of wood laid over it. The wood must have been previously creosoted, in the same manner as railway sleepers. This mode admits of easy examination. Iron pipes must, however, be used if the lines have to pass under roads, etc., where there is any heavy traffic. And it must be borne in mind that however carefully the iron pipes, etc., be cemented at the joints, to make them watertight, there will always be more electrical leakage in underground lines than in overhead ones. In certain rare cases it may be needful to useironwires for this purpose instead of copper; in this case, as iron is six or seven times a worse conductor than copper, a much heavier wire must be employed to get the same effect. In otherwords, where iron wire is used, its section must be not less than seven times that of the copper wire which it replaces.
§ 70. It is always preferable, where great distance (and, consequently, greater expense) do not preclude it, to use wire for the leading as well as for the returning circuit. Still, where for any reason this is not practicable, it is perfectly admissible and possible to make a good return circuit through theearth, that is to make the damp soil carry the return current (see§ 37). As recommended at the section just quoted, this earth circuit must have at each extremity a mass of some good conductor plunged into the moist ground. Intowns, where there are plenty of water mains and gas mains, this is a matter of no difficulty, the only point being to ensuregoodcontact with these masses of metal. In other places a hole must be dug into the ground until the point of constant moisture is reached; in this must be placed a sheet of lead or copper, not less than five square feet surface, to which theearthwires are soldered, the hole then filled in with ordinary coke, well rammed down to within about six inches of the surface, and then covered up with soil well trodden down. In making contact with water or gas pipes, care must be taken to see that these aremainpipes, so that theydolead to earth, and not to a cistern or meter only, as, if there are any white or red lead joints the circuit will be defective. To secure a good contact with an iron pipe, bare it, file its surface clean, rub it over with a bit of blue stone (sulphate of copper) dipped in water; wipe it quitedry, bind it tightly and evenly round with some bare copper wire (also well cleaned), No. 16 gauge. Bring the two ends of the wire together, and twist them up tightly for a length of three or four inches. Now heat a large soldering bit, put some resin on the copper wire, and solder the wire, binding firmly down to the iron pipe. Do likewise to the projecting twist of wire, and to this twist solder the end of thereturnwire. On no account should the two oppositeearthwires be soldered to water mains and gas mains at the same time, since it has been found that the different conditions in which these pipes find themselves is sufficient to set up a current which might seriously interfere with the working of the battery proper. Sometimes there is no means of getting a goodearthexcept through the gas main: in this case we must be careful to get to the street side of the meter, for the red lead joints will prevent good conductivity being obtained. In out of the way country places, if it is possible to get at the metal pipe leading to the well of a pump, a very good "earth" can be obtained by soldering the wires to that pipe, in the same manner as directed in the case of the water main. The operator should in no case be contented with a merely twisted joint, for the mere contact of the two metals (copper and iron) sets up in the moist earth or air a little electric circuit of its own, and this speedily rusts through and destroys the wires. The following suggestions, by Messrs. Gent, on the subject of wiring, are so good, that we feel that we shall be doing real service to the reader to quote them here in full:—
"1st.—The description of wire to be used. It is of the utmost importance that all wires used for electric bell purposes be of pure copper and thoroughly well insulated. The materials mostly employed for insulating purposes are indiarubber, gutta-percha, or cotton saturated with paraffin. For ordinary indoor work, in dry places, and for connecting doors and windows with burglar alarms, or for signalling in case of fire, indiarubber and cotton covered wires answer well; but for connecting long distances, part or all underground, or along walls, or in damp cellars or buildings, gutta-percha covered wire is required, but it should be fixed where it will not be exposed to heat or the sun, or in very dry places, as the covering so exposed will perish, crack, and in time fall off. This may be, to some extent, prevented by its being covered with cotton; but we recommend for warm or exposed positions a specially-prepared wire, in which rubber and compound form the insulating materials, the outside being braided or taped.
"For ordinary house work, we refer to lay a wire of No. 18 or 20 copper, covered to No. 14 or 11 with gutta-percha, and an outer covering of cotton, which we called the 'battery' wire, this being the wire which conveys the current from the battery to every push, etc., no matter how many or in what position. The reason for selecting this kind is, that with the gutta-percha wires the joints may be more perfectly covered and made secure against damp. This is of the utmost importance in the case of 'battery wires,' as the current is alwayspresent and ready to take advantage of any defect in the insulation to escape to an adjoining wire, or to 'earth,' and so cause a continuous waste of current. The wires leading from the pushes to the signalling apparatus or bell we call the 'line' wires. In these, and the rest of the house wires, the perfect covering of the joints is important. Forline wireswe usually prefer No. 18 or 20 copper, covered with indiarubber, and an outer coating of cotton, well varnished. In joining the 'battery wires,' the place where the junction is to be made must be carefully uncovered for the distance of about an inch; the ends of the wire to be joined, well cleaned, and tightly twisted together; with the flame of a spirit lamp or candle the joint must be then heated sufficiently to melt fine solder in strips when held upon it, having first put a little powdered resin on the joint as a flux; the solder should be seen to run well and adhere firmly to the copper wire. A piece of gutta-percha should then be taken and placed upon the joint while warm, and with the aid of the spirit lamp and wet fingers, moulded round until a firm and perfect covering has been formed.On no account use spiritsin soldering. With theline wire, it is best, as far as possible, to convey it all the way from the push to the signal box or bell inone continuouslength. Of course, when two or more pushes are required to the same wire, a junction is unavoidable. The same process of joining and covering, as given for the battery wire, applies to the line wire. Where many wires are to be brought down to one position, a large tube may be buried in the wall, or a woodcasing fixed flush with the plaster, with a removable front. The latter plan is easiest for fixing and for making alterations and additions. For stapling the wires, in no case should the wires be left naked. When they pass along a damp wall, it is best to fix a board andlooselystaple them.In no case allow more than one wire to lie under the same staple, and do not let the staples touch one another. In many cases, electric bells have been an incessant annoyance and complete failure, through driving the staplestight up to the wires, and several wires to the same staple,—this must not be done on any account. A number of wires may be twisted into a cable, and run through a short piece of gutta-percha tube, and fastened with ordinary gas hooks where it is an advantage to do so. In running the wires, avoid hot water pipes, and do not take them along the same way as plumber pipes. Underground wires must be laid between pieces of wood, or in a gas or drain pipe, and not exposed in the bare earth without protection, as sharp pieces of stone are apt to penetrate the covering and cause a loss; in fact, in this, as in every part of fixing wires, the best wire and the best protection is by far the cheapest in the end. The copper wire in this case should not be less than No. 16B.W.G., covered with gutta-percha, to No. 9 or 10B.W.G., and preferably an outer covering of tape or braid well tarred. Outside wire, when run along walls and exposed to the weather, should be covered with rubber and compound, and varnished or tarred on an outer covering of tape or braid. Hooks or staples must be well galvanised to preventrusting, and fixed loosely. If the wire is contained within an iron pipe, a lighter insulation may be used:but the pipe must be watertight. In a new building, wires must be contained within zinc or copper bell tubes. A ⅜ inch tube will hold two wires comfortably. The tubes should be fixed to terminate in the same positions in the rooms as ordinary crank bell levers,—that is, about three feet from the floor. At the side of the fireplace a block of wood should be fixed in the wall before any plaster is put on, and the end of the tube should terminate in the centre of the same. A large nail or screw may be put in to mark the place, so that the end of the tube may be found easily when the plastering is finished. Bend the tube slightly forward at the end, and insert a short peg of wood to prevent dirt getting into the tube. Do the same at the side of, or over the bed in bedroom. If the tubes are kept clean, the wires may be easily drawn up or down as the case may require. The best way is to get a length of ordinary copper bell wire, No. 16, sufficient to pass through the tube, and having stretched it, pass it through and out at the other end. Here have your coils of insulated wire, viz., one battery wire, which is branched off to every push, and one line wire, which has to go direct to the indicator or bells, and having removed a short portion of the insulation from the end of each, they are tied to the bare copper wire and drawn through. This is repeated wherever a push is to be fixed throughout the building. In making connection with binding screws or metal of any kind, it is of the utmost importance that everything should beperfectly clean.Jointsin wire, whether tinned or untinned,must be soldered and covered. We cannot impress this too earnestly on fixers. Never bury wires in plaster unprotected, and in houses in course of erection, thetubesonly should be fixed until the plastering is finished, the wires to be run in at the same time that the other work is completed."
Fig. 75.Fig. 75.
Fig. 75.
§ 71. The wires having been laid by any of the methods indicated in the preceding five sections, the fixer is now in a position toconnect up. No two houses or offices will admit of this being done inexactlythe same way; but in the following sections most of the possible cases are described and illustrated, and the intelligent fixer will find no difficulty, when he has once grasped the principle, in making those trifling modifications which the particular requirements may render necessary. The first and simplest form, which engages our attention, is that of asingle bell, battery, and push, connected by wire only. This is illustrated atFig. 75. Here we see that the bell is connected by means of one of the wires to the zinc pole of the battery, the push or other contact being connected to the carbon pole of the same battery. A second wire unites the other screw of the push or contact with the second binding screw of the bell. There is no complete circuit until the push is pressed, when the current circulates from the carbon or positive pole of the battery, through thecontact springs of the push, along the wire to the bell, and then back again through the under wire to the zinc or negative pole of the battery.[15]It must be clearly understood that the exact position of battery, bell, and push is quite immaterial. What is essential is, that the relative connections between battery, bell, and push be maintained unaltered.Fig. 76shows the next simplest case, viz., that in which a single bell and push are worked by a single cell through an "earth" return (see§ 70). Here the current is made to pass from the carbon pole of the battery to the push, thence along the line wire to the bell. After passing through the bell, it goes to the right-hand earth-plateE, passing through the soil till it reaches the left-hand earth-plateE, thence back to the zinc pole of the battery. It is of no consequence to the working of the bell whether the battery be placed between the push and the left-hand earth-plate, or between the bell and the right-hand earth-plate; indeed, some operators prefer to keep the battery as near to the bell as possible. AtFig. 77is shown the mode by which a single battery and single bell can be made to ring from two (or more) pushes situated in different rooms. Here it is evident that, whichever of the twopushes be pressed, the current finds its way to the bell by the upper wire, and back home again through the lower wire; and, even if both pushes are down at once, the bell rings just the same, for both pushes lead from the same pole of the battery (the carbon) to the same wire (the line wire).
Fig. 76.Fig. 76.
Fig. 76.
Fig. 77.Fig. 77.
Fig. 77.
InFig. 78, we have a slight modification of the same arrangement, a front-doorpullcontact being inserted in the circuit; and here, in view of the probably increased resistance of longer distance,twocells are supposed to be employed instead ofone, and these are coupled up in series (§ 40), in order to overcome this increased resistance.
Fig. 78.Fig. 78.
Fig. 78.
The next case which may occur is where it is desired to ring two or more bells from one push. There are two manners of doing this. The first mode is to make the current divide itself between the two bells, which are then said to be "in parallel." This mode is well illustrated both at Figs.79and80. As in these cases the current has to divide itself among the bells, larger cells must be used, to provide for the larger demand; orseveral cells may be coupled up in parallel (§ 40). AtFig. 79is shown the arrangement for two adjoining rooms; atFig. 80, that to be adopted when the rooms are at some distance apart. If, as shown atFig. 81, a switch similar to that figured in the cutFig. 64be inserted at the point where the line wires converge to meet the push, it is possible for the person using the push to ring both bells at once, or to ring either the right-hand or the left-hand bell at will, according to whether he turns the arm of the switch-lever on to the right-hand or left-hand contact plate.
Fig. 79.Fig. 79.
Fig. 79.
Fig. 80.Fig. 80.
Fig. 80.
Fig. 81.Fig. 81.
Fig. 81.
The second mode of ringing two or more bells from one push is that of connecting one bell to the other, the right-hand binding screw of the one to the left-hand binding screw of the next, and so on, and then connecting up the whole series of bells to the push and battery, as if they were a single bell. This mode of disposing the bells is called theseriesarrangement. As we have already noticed at§ 63, owing to the difference in the times at whichthe different contact springs of the various bells make contact, this mode is not very satisfactory. If the bells are single stroke bells, they work very well in series; but, to get trembling bells to work in series, it is best to adopt the form of bell recommended by Mr. F. C. Allsop. He says: "Perhaps the best plan is to use the form of bell shown atFig. 82, which, as will be seen from the figure, governs its vibrations, not by breaking the circuit, but by shunting its coils. On the current flowing round the electro-magnet, the armature is attracted, and the spring makes contact with the lower screw.There now exists a path of practically no resistance from end to end. The current is therefore diverted from the magnet coils, and passes by the armature and lower screw to the next bell, the armature falling back against the top screw, and repeating the previous operation so long as the circuit is closed. Thus, no matter how many bells there be in the series, the circuit is never broken. This form of bell, however, does not ring so energetically as the ordinary form, with a corresponding amount of battery power."
Fig. 82.Fig. 82.
Fig. 82.
Fig. 83.Fig. 83.
Fig. 83.
Fig. 83illustrates the mode in which a bell, at a long distance, must be coupled up to work with a local battery and relay. The relay is not shown separately, but is supposed to be enclosed in the bell case. Here, on pressing the push at the external left-hand corner, the battery current passes into the relay at the distant station, and out at the right-hand earth-plateEreturning to the left-hand earth-plateE. In doing this, it throws in circuit (just as long as the push is held down) the right-hand local battery, so that the bell rings by the current sent by the local battery, the more delicate relay working by the current sent from the distant battery.
Fig. 84.Fig. 84.
Fig. 84.
Fig. 85.Fig. 85.
Fig. 85.
AtFig. 84, we have illustrated the mode of connecting up a continuous ringing bell, with a wire return. Of course, if the distance is great, or a roadway, etc., intervene, an overhead line and an earth plate may replace the lines shown therein, or both lines may be buried. It is possible, by using a Morse key (Fig. 65) constructed so as to make contact in one direction whennotpressed down, and in the otherwhenpressed down, to signal from either end of a circuit, using only one line wire and one return. The mode of connecting up for this purpose is shown atFig. 85. At each end we have a battery and bell, with a double contact Morse key as shown, the Morse key at each end being connected through the intervention of the line wire through the central stud. The batteries and bells at eachstation are connected to earth plates, as shown. Suppose now we depress the Morse key at the right-hand station. Since by so doing, we lift the back end of the lever, we throw our own bell out of circuit, but make contact between our battery and the line wire. Therefore the current traverses the line wire, enters in the left-hand Morse key, and, since this is not depressed, can, and does, pass into the bell, which therefore rings, then descends to the left-hand earth-plate, returning along the ground to the battery from whence it started at the right-handE. If, on the contrary, theleft-hand Morse key be depressed, while the right-hand key is not being manipulated, the current traverses in the opposite direction, and the right-hand bell rings. Instead of Morse keys,double contactpushes (that is, pushes making contact in one direction whennotpressed, and in the oppositewhenpressed) may advantageously be employed. This latter arrangement is shown atFig. 86.
Fig. 86.Fig. 86.
Fig. 86.
It is also possible, as shown atFig. 87, to send signals from two stations, using but one battery (which, if the distance is great, should be of a proportionate number of cells), two bells, and two ordinary pushes. Threewires, besides the earth-plate or return wire, are required in this case. The whole of the wires, except thereturn, must be carefully insulated. Suppose in this case we press the right-hand button. The current flows from the battery along the lower wire through this right-hand push and returns to the distant bell along the top wire, down the left-hand dotted wire back to the battery, since it cannot enter by the left-hand press, which, not being pushed, makes no contact. The left-hand bell therefore rings. If, on the other hand, the left-hand push be pressed, the current from the carbon of the battery passes through the left-hand push, traverses the central line wire, passes into the bell, rings it, and descends to the right-hand earth plateE, traverses the earth circuit till it reaches the left-hand earth plateE, whence it returns to the zinc pole of the battery by the lower dotted line.
Fig. 87.Fig. 87.
Fig. 87.
Fig. 88shows how the same result (signalling in both directions) may be attained, using only two wires, with earth return, and two Morse keys. The direction of the current is shown by the arrows. Both wires must be insulated andeither carried overhead or underground, buried in tubes.Fig. 89shows the proper mode of connecting the entire system of bells, pushes, etc., running through a building. The dotted lines are the wires starting from the two poles of the battery (which should consist of more cells in proportion as there is more work to do), the plain lines being the wires between the pushes and the bell and signalling box. In this illustration a door-pull is shown to the extreme left. Pendulum indicators are usually connected up as shown in this figure, except that the bell is generally enclosed in the indicator case. The wire, therefore, has to be carried from the left-hand screw of the indicator case direct to the upper dotted line, which is the wire returning to the zinc pole of the battery. N.B.—When the wires from the press-buttons are connected with the binding-screw, of the top of or inside of the indicator case, the insulating material of the wires, at the point where connection is to be made, must be removed, and the wirescarefully cleanedandtightly clamped down.
Fig. 88.Fig. 88.
Fig. 88.
Fig. 89.Fig. 89.
Fig. 89.
When it is desired to connect separate bells to ringin other parts of the building, the quickest way is to take a branch wire out of the nearestbattery wire(the wire coming from the carbon pole), and carry it to the push or pull, from thence to the bell, and from the bell back to the zinc of the battery.
§ 72. We should advise the fixer always to draw out a little sketch of the arrangement he intends to adopt in carrying out any plan, as any means of saving useless lengths of wire, etc., will then easily be seen. In doing this, instead of making full sketches of batteries, he may use the conventional signs▍▏for each cell of the battery, the thick stroke meaning the carbon, the thin one the zinc. Pushes may be represented by (·), earth-plates by [E] and pulls, switches, &c., as shown in the annexed cut,Fig. 90, which illustrates a mode of connecting up a lodge with a house, continuous bells being used, in such a way that the lodge bell can be made to ring from the lodge pull, the house bell ringing or not, according to the way the switch (shown at top left-handcorner) is set. As it is set in the engraving, only the lodge bell rings.
Fig. 90.Fig. 90.
Fig. 90.
§ 73. There are still two cases of electric bell and signal fitting, to which attention must be directed. The first is in the case ofships. Here all the connections can be made exactly as in a house, the only exception to be made being that the indicators must not be of thependulum, or other easily displaced type; but either of the form shown atFig. 67or68, in which the electro-magnet has to lift a latch to release the fall or drop, against a pretty stiff spring. Besides being thus firmly locking, so as not to be affected by the ship's motion, all the wood work should be soaked in melted paraffin wax, the iron work japanned, and the brass work well lacquered, to protect all parts from damp. The second case requiring notice is that oflifts. Every well-appointed lift should be fitted with electric bells andindicators. In the cab of the lift itself should be placed an electric bell, with as many double contact pushes and indicators as there are floors to be communicated with. At the top and at the bottom of the left shaft, as near to the landing side as possible, must be set two stout wooden blocks (oak, elm, or other non-perishable wood). From top to bottom of the shaft must then be stretched, in the same manner as a pianoforte is strung, on stout metal pins, with threading holes and square heads, as many No. 12 or 14 bare copper wires as there are floors or landings, and two more for the battery and return wire respectively. Care must be taken that these wires are strung perfectly parallel, and that they are stretched quite taut, but not strained, otherwise they will surely break. To the top of the cab, and in connection in the usual manner by wires with the bell and indicator (which, as in the case of ships, must be of the locking type, lest the jolts of the cab disturb their action) must be attached a number of spoonbill springs, which press against the naked wires running down the shaft. The shape of these springs (which should be of brass) at the part where they press against the bare wires, is similar to that of the spoon break of a bicycle. Some operators use rollers at the end of the spring instead of spoonbills, but these latterrubthe wires and keep up good contact, while the rollers slip over the wires and do not keep them clean. By means of these springs, the current from the batteries, which are best placed either at the top of the lift itself, or in one of the adjacent rooms (never at the bottom of the shaft, owing to the damp which always reigns there),can be taken off and directed where it is desired, precisely as if the batteries were in the cab itself. It is usual (though not obligatory) to use the two wiresfurthestfrom the landing as the go and return battery wires, and from these, through the other wires, all desired communication with the landings can be effected. To obtain this end, it will be necessary to furnish every landing with a double contact push and bell, and each bell and push must be connected up to the shaft wires in the following mode:—
A wire must be led from thelowercontact spring of the double contact push, to themain battery carbon wirein the shaft. A second wire is led from theupper contact stopof the double contact push to the bell, and thence to themain battery zinc wireon the shaft. Lastly, a third wire is taken from theupper contact springof the push and connected to that particular wire in the shaft which by means of the spoonbill springs connects the particular push and indicator in the cab, destined to correspond with it. It will be seen that with the exception of using the rubbing spoonbill springs and return wires in the shaft, this arrangement is similar to that illustrated atFig. 87.
Fig. 91.Fig. 91.
Fig. 91.
A glance atFig. 91will render the whole system of wiring and connecting up with lifts and landing, perfectly clear. In connecting the branch lines to the main bare copper wires in the shaft, in order that the spoonbill springs should not interfere with them, they (the ends of the branch wires) must be bent at right angles, like a letter L, and the upright portion soldered neatlyto thebackof the shaft wire. Any solder which may flow over to thefrontof the wire must be carefully scraped off to prevent any bumps affecting the smooth working of the contact springs. It will be evident on examination ofFig. 91, that if any of the pushes on the landings be pressed, the circuit is completed between the battery at the top, through the two battery wiresto the bell and one of the indicators to the cab, and, on the other hand, that if a push be pressed in the cab, a corresponding bell on the landing will be rung, precisely as inFig. 87.
Some fitters employ a many-stranded cable to convey the current to and from the battery to the cab and landing, instead of the system of stretched wires herein recommended; but this practice cannot be advocated, as the continual bending and unbending of this cable, repeated so frequently every day, soon breaks the leading wires contained in the cable.
Fig. 92.Fig. 92.
Fig. 92.
§ 74. In many cases where a "call" bell alone is required, the battery may be entirely dispensed with, and a small dynamo (§ 15) employed instead. The entire apparatus is then known as the "magneto-bell," and consists essentially of two parts, viz., the generator,Fig. 92, and the bell,Fig. 93. Thegeneratororinductorconsists of an armature, which by means of a projecting handle and train of wheels can be revolved rapidly between the poles of a powerful magnet; the whole being enclosed in a box. The current produced by the revolution of the armature is led to the two binding screws at the top of the box. By means of two wires, or one wire and an earth circuit, the current is led to thereceiver or bell case,Fig. 93. Here, there are usually two bells, placed very near one another, and the armature attached to the bell clapper is so arranged between the poles of the double-bell magnets, that it strikes alternately the one and the other, so that a clear ringing is kept up as long as the handle is being turned at the generator.
Fig. 93.Fig. 93.
Fig. 93.
Fig. 94.Fig. 94.
Fig. 94.
If acombinedgenerator and bell be fitted at each end of a line, it becomes possible to communicate both ways; one terminal of each instrument must be connected to the line, and the other terminal on each to earth. A combined generator and bell is shown atFig. 94. These instruments are always ready for use, require no battery or press-buttons. The generator,Fig. 92, will ring seven bells simultaneously, if required, so powerful is the current set up; and by using a switch any number of bells, placed in different positions, can be rung, by carrying a separate wire from the switch to the bell.
Fig. 95.Fig. 95.
Fig. 95.
§ 75. Our work would not be complete unless we pointed out the means necessary to detect faults in our work. In order to localise faults, two things are requisite: first, a means of knowing whether the battery itself is working properly, that is to say, giving the dueamountof current of the rightpressure, or E.M.F.; secondly, a means of detecting whether there is leakage, or loss ofcurrent, or break of circuit in our lines. Fortunately, the means of ascertaining these data can be all combined in one instrument, known as a linesman's galvanometer or detector, of which we give an illustration atFig. 95. It will be remembered (§ 10) that if a current be passed over or under a poised magnetic needle, parallel to it, the needle is immediately deflected out of the parallel line, and swings round to the right or left of the current, according to thedirectionof the current; likewise that the needle is deflected farther from the original position as the current becomes stronger. The deflections, however, are not proportionate to the strength of the current, being fairly so up to about 25 to 30 degrees of arc out of the original position, but being very much less than proportionate to the current strength as the needle gets farther from the line of current; so that a current of infinite strength would be required to send the needle up to 90°. On this principle the detector is constructed. It consists of a lozenge-shaped magnetic needle, suspended vertically on a light spindle, carrying at one end a pointer, which indicates on a card, or metal dial,the deflection of the needle. Behind the dial is arranged a flat upright coil of wire (or two coils in many cases) parallel to the needle, along which the current to be tested can be sent. The needle lies between the front and back of the flat coil. The whole is enclosed in a neat wooden box, with glazed front to show the dial, and binding screws to connect up to the enclosed coil or coils. If the coil surrounding the needle be of a few turns of coarse wire, since it opposes little resistance to the passage of the current, it will serve to detect the presence of largequantitiesof electricity (many ampères) at a low pressure; this is called aquantitycoil. If, on the other hand, the coil be one of fine wire, in many convolutions, as it requires morepressure, or E.M.F., or "intensity" to force the current through the fine high-resistance wire, the instrument becomes one fitted to measure the voltage orpressureof the current, and the coil is known as the "intensity." If both coils are inserted in the case, so that either can be used at will, the instrument is capable of measuring either the quantity of electricity passing, or the pressure at which it is sent, and is then known as a quantity and intensity detector. No two galvanometers give exactly the same deflection for the same amount of current, or the same pressure; the fitter will therefore do well to run out a little table (which he will soon learn by heart) of the deflectionhisinstrument gives with 1, 2, 3, 4, 5 and 6 Leclanché'scoupled in parallel, when connected with the quantity coil. He will find the smaller sizes give less current than the larger ones. In testing thedeflections given by the intensity coil, he must remember to couple his cellsin series, as he will get no increase intensionorpressureby coupling up in parallel. In either case the cells should be new, and freshly set up, say, within 24 hours. As some of my readers may like to try their skill at constructing such a detector, I transcribe the directions given in "Amateur work" by Mr. Edwinson:—
§ 76. "Such an instrument, suitable for detecting the currents in an electric bell circuit, may be made up at the cost of a few shillings for material, and by the exercise of a little constructive ability. We shall need, first of all, a magnetised needle; this can be made out of a piece of watch spring. Procure a piece of watch spring two inches long, soften it by heating it to redness, and allowing it to cool gradually in a bed of hot ashes; then file it up to the form of a long lozenge, drill a small hole in the centre to receive the spindle or pivot, see that the needle is quite straight, then harden it by heating it again to a bright red and plunging it at once into cold water. It now has to be magnetised. To do this, rub it on a permanent horse-shoe, or other magnet, until it will attract an ordinary sewing needle strongly, or wrap it up in several turns of insulated line wire, and send many jerky charges of electricity from a strong battery through the wire. When it has been well magnetised, mount it on a spindle of fine hard wire, and secure it by a drop of solder. We will next turn our attention to the case, bobbin, or chamber in which the needle has to work. This may be made out of cardboard entirely, or the end pieces may be made of ivory or ebonite, or it may be made out of thin sheet brass; for our purpose we will choose cardboard. Procure a piece of stout cardboard 4¾ inches long by 2 inches wide, double it to the form of a Tãndstickor match-box, and pierce it in exactly opposite sides, and in the centre of those sides with holes for the needle spindle. Now cut another piece of stout, stiff cardboard 2¾ inches long by ¾ inch wide, and cut a slit with a sharp knife to exactly fit the ends of the case or body already prepared. The spindle holes must now be bushed with short lengths of hard brass or glass bugles, or tubing, made to allow the spindle free movement, and these secured in position by a little melted shellac, sealing-wax, or glue. The needle must now be placed in the case, the long end of the spindle first, then the short end in its bearing; then, whilst the case with the needle enclosed is held between the finger and thumb of the left hand, we secure the joint with a little glue or with melted sealing-wax. The end-pieces are now to be put on, glued, or sealed in position, and set aside to get firm, whilst we turn our attention to other parts. The case, 5 inches by 4 inches by 2 inches in depth, may be improvised out of an old cigar-box, but is best made of thin mahogany or teak, nicely polished on the outside, and fitted with a cover sliding in a groove, or hinged to form the back of the instrument. The binding screws should be of the pattern known as the telegraph pattern, fitted with nuts, shown atFig. 27. A small brass handle to be fitted to the top of the instrument,will also be handy. A circular piece of smooth cardboard 3¼ inches in diameter, with a graduated arc, marked as shown inFig. 95, will serve the purpose of a dial, and a piece of thin brass, bent to the form of ┏━┓, will be required as a needle guard. The face of the dial may be a circular piece of glass, held in a brass ogee, or a hole the size of the dial may be cut in a piece of thin wood; this, glazed on the inside with a square of glass, may be made to form the front of the instrument over the dial. An indicating needle will also be required for an outside needle; this is usually made of watch spring, and nicely blued; but it may be made of brass or any other metal, one made of aluminium being probably the best on account of its lightness. It must be pierced with a hole exactly in the centre, so as to balance it as the beam of scales should be balanced, and should one end be heavier than the other it must be filed until they are equal.
We will now turn our attention to the coil.
Procure sixpennyworth of No. 36 silk-covered copper wire and wind three layers of it very evenly on the coil case or bobbin, being careful in passing the needle spindle not to pinch it or throw it out of truth. When this has been wound on, it will be found that one end of the wire points to the left and the other end to the right. These are destined to be connected to the under side of the binding screws shown on the top ofFig. 95. We therefore secure them to their respective sides with a touch of sealing wax, and leave enough wire free at the ends to reach the binding screws—say, about 6 inches.It is handy to have an additional coil for testing strong currents, and as this may be combined in one instrument at a trifle additional cost, we will get some line wire (No. 22) and wind six or eight turns of it around the coil outside the other wire; one end of this wire will be attached to an additional binding screw placed between the others, and the other end to left binding screw shown. The coil thus prepared may now be mounted in position. Pierce the board dial and the wood at its back with a hole large enough for the needle spindle to pass through from the back to the centre of the dial. See that the thick end of the inside needle hangs downwards, then place the coil in the position it is intended to occupy, and note how far the needle spindle protrudes on the face of the dial. If this is too long, nip off the end and file it up taper and smooth until it will work freely in a hole in the needle guard, with all parts in their proper places. This being satisfactory, secure the coil in its place by sealing wax, or, better still, by two thin straps of brass, held by screws at each end, placed across the coil. Now clean the free ends of the coil wires, insert them under the nuts of the binding screws, fix the indicating needle on the end of the spindle outside, and see that it hangs in a vertical position with the inside needle when the instrument is standing on a level surface. Secure it in this position, screw on the needle guard, fasten on the glass face, and the instrument will be complete.
§ 77. Provided thus with an efficient detector, the fitter may proceed to test his work. In cases ofnew installations, take the wire off the carbon binding screw of the battery and attach it to one screw of the galvanometer (on the intensity coil side), next attach a piece of wire from the other binding screw of the galvanometer (the central one) so as to place the galvanometer in circuit.There should be no movement of the needle, and in proportion to the deflection of the needle, so will the loss or waste be. If loss is going on, every means must be used to remedy it. It is of the utmost importance to the effective working of the battery and bells that not theslightest leakageorlocal actionshould be allowed to remain. However slight such loss may be, it will eventually ruin the battery. Let damp places be sought out, and the wires removed from near them. Bad or injured coverings must also be looked for, such as may have been caused by roughly drawing the wires across angular walls, treading on them, or driving staples too tightly over them. Two or more staples may be touching, or two or more wires carelessly allowed to lie under one staple. The wire may have been bared in some places in passing over the sharp edges of the zinc tube. The backs of the pushes should be examined to see if too much wire has been bared, and is touching another wire at the back of the push-case itself. Or the same thing may be taking place at the junction with the relays or at the indicator cases. Should the defect not be at any of these places, the indicator should next be examined, and wire by wire detached (not cut) until the particular wire in which the loss is going on has been found. This wire should then be traced until the defecthas been discovered. In testing underground wires for a loss or break, it will be necessary first to uncouple thedistantend, then to disconnect the other end from the instruments, and attach the wire going underground to the screw of the galvanometer. A piece of wire must then be taken from the other screw of the detector to the carbon end of the battery, and a second wire from the zinc end of the battery to the earth plate or other connection. Proceeding to that part of the wire where the injury is suspected, the wire is taken up, and a temporary earth connection having been made (water main, gas pipe, etc.), and by means of a sharp knife connected with this latter, the covering of the suspected wire penetrated through to the wire, so as to make a good connection between this suspected wire and the temporary earth plates. If, when this is done, the needle is deflected fully, the injury is farther away from the testing end, and other trials must be made farther on, until the spot is discovered. Wherever the covering of the wire has been pierced for testing, it must be carefully recovered, finished off with Prout's elastic glue, or gutta-percha, and made quite sound. The connections with the earth plates very frequently give trouble, the wires corrode or become detached from the iron pipes etc., and then the circuit is broken.
§ 78. When the fitter is called to localise defects which may have occurred in an installation which has been put up some time, before proceeding to work let him ask questions as to what kind of defect there is, and when and where it evinces itself. If all thebells have broken down, and will not ring, either the battery or the main go and return wires are at fault. Let him proceed to the battery, examine the binding screws and connected wires for corrosion. If they are all right, let the batteries themselves be tested to see if they are giving the right amount of current. This should be done with the quantity coil of the detector. Should the battery be faulty, it will be well to renew the zincs and recharge the battery, if the porous cell be still in good condition; if not, new cells should be substituted for the old ones. Should the battery be all right, and still none of the bells ring, a break or bad contact, or short circuit in the main wires near the battery may be the cause of the mischief. If some bell rings continuously, there must be a short circuit in the push or pushes somewhere; the upper spring of one of the pushes may have got bent, or have otherwise caught in the lower spring.Pullsare very subject to this defect. By violent manipulations on the part of mischievous butcher or baker boys, the return spring may be broken, or so far weakened as not to return the pull into the "off" position. If, the batteries being in good order, any bell rings feebly, there is either leakage along its line, or else bad contact in the push or in the connections of the wires to and from the push. There should be platinum contacts at the ends of the push springs; if there are not, the springs may have worked dirty at the points of contact, hence the poor current and poor ringing. It is seldom that the bells themselves, unless, indeed, of the lowest quality,give any serious trouble. Still the set screw may have shaken loose (which must then be adjusted and tightened up), or the platinum speck has got solder on its face and therefore got oxidised. This may be scraped carefully with a penknife until bright. Or, purposely or inadvertently, no platinum is on the speck at all, only the solder. A piece of platinum foil should be soldered on the spot, if this is so. Or again (and this only in very bad bells), the electro-magnets being of hard iron, may have retained a certain amount ofpermanent magnetism, and pull the armature into permanent contact with itself. This can be remedied by sticking a thin piece of paper (stamp paper will do) over the poles of the magnet, between them and the armature. In no case should the fittercutordraw upout of tubes, etc., any wire or wires, without having first ascertained that the fault is in that wire; for, however carefully joints are made, it is rare that the jointed places are so thoroughly insulated as they were before the cutting and subsequent joining were undertaken. To avoid as much as possible cutting uselessly, let every binding screw be examined and tightened up, and every length of wire, which it is possible to get at, be tested for continuity before any "slashing" at the wires, or furious onslaughts on the indicator be consummated.
In conclusion, I beg to record my thanks for the very generous assistance which I have received in the compilation of the foregoing pages from the electrical firms of Messrs. Blakey Emmot, Binswanger, Gent, Judson, Jensen, and Thorpe.