Electric Bells and All About Them Part 9

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.

[Ill.u.s.tration: Fig. 74.]

-- 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 [box open up], 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 pa.s.s 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 use _iron_ wires 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 other words, 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 the _earth_, 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 ma.s.s of some good conductor plunged into the moist ground. In _towns_, where there are plenty of water mains and gas mains, this is a matter of no difficulty, the only point being to ensure _good_ contact with these ma.s.ses 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 the _earth_ wires are soldered, the hole then filled in with ordinary c.o.ke, 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 are _main_ pipes, so that they _do_ lead 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 quite dry, 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 the _return_ wire. On no account should the two opposite _earth_ wires 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 good _earth_ except 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 always present 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. For _line wires_ we 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 spirits_ in soldering. With the _line wire_, it is best, as far as possible, to convey it all the way from the push to the signal box or bell in _one continuous_ length. 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 wood casing 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 pa.s.s along a damp wall, it is best to fix a board and _loosely_ staple 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 staples _tight 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. 16 B.W.G., covered with gutta-percha, to No. 9 or 10 B.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 prevent rusting, 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 3/8 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 pa.s.s through the tube, and having stretched it, pa.s.s 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 be _perfectly clean_. _Joints_ in 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, the _tubes_ only should be fixed until the plastering is finished, the wires to be run in at the same time that the other work is completed."

[Ill.u.s.tration: 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 to _connect up_.

No two houses or offices will admit of this being done in _exactly_ the same way; but in the following sections most of the possible cases are described and ill.u.s.trated, 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 a _single bell, battery, and push_, connected by wire only. This is ill.u.s.trated at Fig. 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 the contact 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. 76 shows 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 pa.s.s from the carbon pole of the battery to the push, thence along the line wire to the bell. After pa.s.sing through the bell, it goes to the right-hand earth-plate E, pa.s.sing through the soil till it reaches the left-hand earth-plate E, 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. At Fig. 77 is 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 two pushes 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).

[Footnote 15: It must be borne in mind that the negative element is that to which the positive pole is attached, and _vice versa_ (see ss. 8 and 9).]

[Ill.u.s.tration: Fig. 76.]

[Ill.u.s.tration: Fig. 77.]

In Fig. 78, we have a slight modification of the same arrangement, a front-door _pull_ contact being inserted in the circuit; and here, in view of the probably increased resistance of longer distance, _two_ cells are supposed to be employed instead of _one_, and these are coupled up in series (-- 40), in order to overcome this increased resistance.

[Ill.u.s.tration: 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 ill.u.s.trated both at Figs. 79 and 80. As in these cases the current has to divide itself among the bells, larger cells must be used, to provide for the larger demand; or several cells may be coupled up in parallel (-- 40). At Fig.

79 is shown the arrangement for two adjoining rooms; at Fig. 80, that to be adopted when the rooms are at some distance apart. If, as shown at Fig. 81, a switch similar to that figured in the cut Fig. 64 be 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.

[Ill.u.s.tration: Fig. 79.]

[Ill.u.s.tration: Fig. 80.]

[Ill.u.s.tration: 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 the _series_ arrangement. As we have already noticed at -- 63, owing to the difference in the times at which the 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 at Fig. 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 pa.s.ses 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."

[Ill.u.s.tration: Fig. 82.]

[Ill.u.s.tration: Fig. 83.]

Fig. 83 ill.u.s.trates 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 pa.s.ses into the relay at the distant station, and out at the right-hand earth-plate E returning to the left-hand earth-plate E. 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.

[Ill.u.s.tration: Fig. 84.]

[Ill.u.s.tration: Fig. 85.]

At Fig. 84, we have ill.u.s.trated 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 when _not_ pressed down, and in the other _when_ pressed 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 at Fig. 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 each station 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, pa.s.s 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-hand E. If, on the contrary, the _left_-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 contact_ pushes (that is, pushes making contact in one direction when _not_ pressed, and in the opposite _when_ pressed) may advantageously be employed. This latter arrangement is shown at Fig. 86.

[Ill.u.s.tration: Fig. 86.]

It is also possible, as shown at Fig. 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. Three wires, besides the earth-plate or return wire, are required in this case. The whole of the wires, except the _return_, must be carefully insulated. Suppose in this case we press the right-hand b.u.t.ton. 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 pa.s.ses through the left-hand push, traverses the central line wire, pa.s.ses into the bell, rings it, and descends to the right-hand earth plate E, traverses the earth circuit till it reaches the left-hand earth plate E, whence it returns to the zinc pole of the battery by the lower dotted line.

[Ill.u.s.tration: Fig. 87.]

Fig. 88 shows 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 and either carried overhead or underground, buried in tubes.

Fig. 89 shows 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 ill.u.s.tration 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-b.u.t.tons 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 wires _carefully cleaned_ and _tightly clamped down_.

[Ill.u.s.tration: Fig. 88.]

[Ill.u.s.tration: Fig. 89.]

When it is desired to connect separate bells to ring in other parts of the building, the quickest way is to take a branch wire out of the nearest _battery 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 [battery] 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 ill.u.s.trates 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-hand corner) is set. As it is set in the engraving, only the lodge bell rings.

[Ill.u.s.tration: 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 of _ships_.

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 the _pendulum_, or other easily displaced type; but either of the form shown at Fig. 67 or 68, 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 j.a.panned, and the bra.s.s work well lacquered, to protect all parts from damp. The second case requiring notice is that of _lifts_. Every well-appointed lift should be fitted with electric bells and indicators. 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 bra.s.s) 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 latter _rub_ the 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 wires _furthest_ from 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 the _lower_ contact spring of the double contact push, to the _main battery carbon wire_ in the shaft. A second wire is led from the _upper contact stop_ of the double contact push to the bell, and thence to the _main battery zinc wire_ on the shaft. Lastly, a third wire is taken from the _upper contact spring_ of 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 ill.u.s.trated at Fig. 87.

[Ill.u.s.tration: Fig. 91.]

A glance at Fig. 91 will 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 neatly to the _back_ of the shaft wire. Any solder which may flow over to the _front_ of the wire must be carefully sc.r.a.ped off to prevent any b.u.mps affecting the smooth working of the contact springs. It will be evident on examination of Fig. 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 wires to 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 in Fig. 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.

-- 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. The _generator_ or _inductor_ consists 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 the receiver 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.

[Ill.u.s.tration: Fig. 92.]

[Ill.u.s.tration: Fig. 93.]

[Ill.u.s.tration: Fig. 94.]