Electric Bells and All About Them

y, the system will surely be continually breaking down, and giving rise to dissatisfaction. It is therefore of the highest importance that

s. 1st, The amount of current (in ampères) required to ring the bell. 2nd, The battery power it is intended to employ. 3rd, The distance to which the lines are to be carried. From practical experience I have found that it is just possible to ring a 2?" bell with ? an ampère of current. Let us consider what this would allow us to use, in the way of batteries and wire, to ring such a bell. The electro-motive force of a single Leclanchè cell is, as we have seen at § 38, about 1·6 volt, and the internal resistance

olts. A

1·60

with one single bell in circuit; and as the difference in price between No. 18 and No. 20 is very trifling, I should strongly recommend the bell-fitter to adhere to No. 18, as his smallest standard size. It would also be well to so proportion the size and arrangement of the batteries and wires, that, at the time of setting up, a current of at least one ampère should flow through the entire circuit. This will allow margin for t

ths per lbs. & 100 yards of

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pairing, or adding on fresh branch circuits. For outdoor work, wire of the same gauge (No. 18) may generally be used, but it must be covered to the thickness of 1/10" with pure gutta-percha, and over this must be wound tape served with Stockholm tar. Wires of this description, either with or without the tarred tape covering, may be obtained from all the leading electricians' sundriesmen. Many firms use copper wire tinned previous to being insulated. This tinning serves two good purposes, 1st, the copper wire does not verdigris so easily; 2ndly, it is more easily soldered. On the other hand, a tinned wire is always a little harder, and presents a little higher resistance. Whenever wires are to be joined together, the ends to be joined must be carefully divested of their covering for a length of about three inches, the copper carefully cleaned by scraping and sand-papering, twisted tightly and evenly together, as shown in Fig. 73 A, and soldered with ordinary soft solder (without spirits), and a little resin or composite candle as a flux. A heavy plumber's soldering iron, or

not do for elect

g.

straightest convenient route from bell to battery, etc., should always be chosen where practicable to facilitate drawing the wire through and to avoi

g.

taple, 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, the blocks to which these are to be fastened must be bedded in the plaster. These blocks may be either square or circular pieces 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 o

vered 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 mo

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

ecting 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 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 pass 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 i

g.

ush 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 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

g.

g.

circuit; and here, in view of the probably increased resistance of longer distance, two cells are supposed to be

g.

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 figur

g.

g.

g.

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 low

g.

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sing 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-plate E returning to the left-hand earth-plate E. In doing this, it throws i

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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, a

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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 othe

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arting 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

g.

g.

is to take a branch wire out of the nearest battery wire (the wire coming from the carbon pole), and c

se 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 l

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t 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 t

e 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 pu

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ht 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 scraped off to prevent any bumps affecting the smooth working of the contact springs. It will be evident on examination of Fig. 91, that if any

ad of the system of stretched wires herein recommended; but this practice cannot be advocated, as the continual bendi

g.

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 t

g.

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each to earth. A combined generator and bell is shown at Fig. 94. These instruments are always ready for use, require no battery or press-buttons. The generator, Fig. 92, will ring seven bells simult

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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 large quantities of electricity (many ampères) at a low pressure; this is called a quantity coil. If, on the other hand, the coil be one of fine wire, in many convolutions, as it requires more pressure, or E.M.F., or "intensity" to force the current through the fine high-resistance

ry 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 4? inches long by 2 inches wide, double it to the form of a T?ndstickor 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 2? inches long by ? 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 mah

rn our attenti

nstrument 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 l

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 defect has been discovered. In testing underground wires for a loss or break, it will be necessary first to uncouple the distant end, 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 th

n 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. Pulls are 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

h I have received in the compilation of the foregoing pages from the electrica

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END

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ARTS, SCIENCES, MANUF

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ok by Sir David Sa

nd Enlarged, with 32 I

a poor compliment, as it is practically the only work on

l Handbook. By S. R. Bottone, Author of "The Dynamo,"

. R. Bottone. With n

epara

dern Point of View. Being the substance of two lectures delivered before the Society of Arts in March,

ations and additions, with the

unt of their historical development, their modern For

UR WORKSHOPS. A Practical H

dy S

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auge" ( ... cotton-covered cop

harge" ( ... losing at the same

"gauge" ( ... 1 foot of No.

t" ( ... of the exact diameter of

is" to "Rivetting is," (Rivetti

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. the possible defects of electric bell

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to "Instead" (Instead of t

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to "electro-magnet" ( ... if the

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t" should perhaps be "Emmott" (... the ele

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f "Ampére" to "Ampère" in the ind