Electric Bells and All About Them: A Practical Book for Practical Men

by Selimo Romeo Bottone

§ 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 mass 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 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 the earth wires 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 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:

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"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 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 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 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."