Electricity for the farm Part 11

[Ill.u.s.tration: Detail of wooden moulding]

If the moulding is run along the walls flush with the ceiling, as is usual, a branch is made for a wall light, or wall tap, by means of a porcelain "T," or branch-block, which provides the means for running the circuit at right angles to itself without letting the wires come in contact with each other where they cross. Separable current taps should be installed in handy places on all circuits, so that small heating devices may be used without removing the lamps from their sockets. The two wires are bared for half an inch where they run through these current taps, and are fastened by means of bra.s.s screws.

_"Multiple" Connections_

All electric devices for this installation--lamps, irons, vacuum cleaners, motors--must be connected _across_ the circuit--that is, bridged, from one wire to the other. This is called _multiple_, or shunt connection. There is only one exception to it, in wiring the house. That one exception is installing a wall switch, the ordinary snap switch. Since this wall switch, is, in effect, merely an instrument, which opens or closes a circuit, it should be connected to only one wire, which is cut to provide two ends for the screw connections in the switch. When a moulding branch is run down from the ceiling to some convenient spot for a snap switch (with which to turn the lights of a room on or off), a porcelain "T" is not used. All that is necessary to do is to loop the bottom wire of the circuit down through the branch moulding, and connect it to the switch at a terminal block, or porcelain base.

In wiring lamp fixtures, No. 14 rubber-covered wire will usually prove too large. For this purpose, No. 18 may be used, with one lamp to each loop. Hanging lamps may not be supported by electric lamp cord itself, if there is more than one lamp in the cl.u.s.ter, because the weight is apt to break the electrical connections. In such a case, the lamp should be supported by a chain, and the twisted cord conveying current to the electric bulbs, is woven in the links of the chain. For the pantry, kitchen, woodshed, barn, etc., a single hanging lamp may be suspended from a fielding rosette, as shown in the cut, provided a single knot is tied inside both the rosette and the lamp socket, to make it secure. This makes a very cheap fixture. The rosette of porcelain will cost 15 cents; the lamp socket 20 cents, and the lamp cord suspending the lamp and carrying the current will cost 1-1/2 cents a foot; while a tin shade will cost another 15 cents.

[Ill.u.s.tration: Detail of simple hanging lamp supported by rosette]

_Official Inspection_

In all communities, your insurance agent must inspect and pa.s.s your wiring before you are permitted to throw the main switch and turn on the electricity. Frequently they require that the moulding be left uncapped, until they have inspected it. If you have more than 660 watts in lamps to a circuit; if your joints are not soldered and well taped; if the moulding is used in any concealed or damp place, the agent is liable to condemn your work and refuse permission to turn on the electricity. However the rules are so clearly defined that it is difficult to go wrong; and a farmer who does his own wiring and takes pride in its appearance is more apt to be right than a professional electrician who is careless at his task. After the work has been pa.s.sed, tack on the moulding capping, with brads, and paint the moulding to match the woodwork.

Wooden moulding wiring is perfectly satisfactory if properly installed. It is forbidden in many large cities, because of the liability of careless workmans.h.i.+p. It should never be installed in damp places, or out of sight. If the work is well done, the system leaves nothing to be desired; and it has the additional advantage of being cheap, and easily done by any farmer who can use carpenter tools. Farmers with moulding machinery can make their own moulding.

The code prescribes it shall be of straight-grained wood; that the raceways for the wires shall be separated by a tongue of wood one-half inch wide; and that the backing shall be at least 3/8 inch thick. It must be covered, inside and out, with at least two coats of moisture-repellant paint. It can be had ready-made for about 2 cents a foot.

_Special Heating Circuits_

If one plans using electricity for heavy-duty stoves, such as ranges and radiators, it is necessary to install a separate heating circuit.

This is the best procedure in any event, even when the devices are all small and suited to lamp circuits. The wire used can be determined by referring to the table for carrying capacity, under the column headed "rubber-covered." A stove or range drawing 40 amperes, would require a No. 4 wire, in moulding. A good plan is to run the heating circuit through the bas.e.m.e.nt, attaching it to the rafters by means of porcelain k.n.o.bs. Branches can then be run up through the floor to places where outlets are desired. Such a branch circuit should carry fuses suitable to the allowed carrying capacity of the wire.

_k.n.o.b and Cleat Wiring_

k.n.o.b and cleat wiring, such as is used extensively for barns and out-buildings, requires little explanation. The wires should not be closer than 2-1/2 inches in open places, and a wider s.p.a.ce is better.

The wires should be drawn taut, and supported by cleats or k.n.o.bs at least every four feet. In case of branch circuits, one wire must be protected from the other it pa.s.ses by means of a porcelain tube. It should never be used in damp places, and should be kept clear of dust and litter, and protected from abrasion.

[Ill.u.s.tration: k.n.o.b and cleat wiring]

k.n.o.b and tube wiring is frequently used in houses, being concealed between walls or flooring. In this case, the separate wires are stretched on adjoining beams or rafters, and porcelain tubes are used, in pa.s.sing through cross beams. For a ceiling or wall outlet, a spliced branch is pa.s.sed through the plaster by means of porcelain tubes or flexible loom.

Wires from the house to the barn should be uniform with transmission wires. At the point of entry to buildings they must be at least six inches apart, and must take the form of the "drop loop" as shown in the ill.u.s.tration. A double-pole entrance switch must be provided, opening downward, with a double-pole fuse. In pa.s.sing over buildings wires must not come closer than 7 feet to flat roofs, or one foot to a ridge roof. Feed-wires for electric motors should be determined from the table of safe carrying capacities, and should be of liberal size.

CHAPTER IX

THE ELECTRIC PLANT AT WORK

Direct-connected generating sets--Belt drive--The switchboard--Governors and voltage regulators--Methods of achieving constant pressure at all loads: Over-compounding the dynamo; A system of resistances; (A home-made electric radiator); Regulating voltage by means of the rheostat--Automatic devices--Putting the plant in operation.

Dynamos may be connected to water wheels either by means of a belt, or the armature may spin on the same shaft as the water wheel itself. The latter is by far the more desirable way, as it eliminates the loss of power through shafting and belting, and does away altogether with the belts themselves as a source of trouble. An installation with the water wheel and armature on the same shaft is called a "direct-connected set" and is of almost universal use in large power plants.

To be able to use such a direct-connected set, the dynamo must be designed to develop its full voltage when run at a speed identical with that of the water wheel. That is, if the dynamo is wound to be run at a speed of 800 revolutions per minute, it must be driven by a water wheel which runs at this speed and can be governed within narrow limits. Small impulse wheels running under great heads attain high speed, and for such wheels it is possible to obtain a suitable dynamo at low cost. For instance, a 12-inch impulse wheel, running under a 200-foot head will develop 6-3/4 horsepower when running at a speed of 875 revolutions per minute. A dynamo for direct coupling to such a wheel should have a rated speed within 5 per cent of 875 r.p.m.; and, as generators of this speed are to be had from the stock of almost all manufacturers, there would be no extra charge.

When it comes to the larger wheels, however, of the impulse type, or to turbines operating under their usual head the question becomes a little more difficult. In such cases, the speed of the water wheel will vary from 150 revolutions per minute, to 400, which is slow speed for a small dynamo. As a general rule, the higher the speed of a dynamo, the lower the cost; because, to lower the speed for a given voltage, it is necessary either to increase the number of conductors on the armature, or to increase the number of field coils, or both.

That means a larger machine, and a corresponding increase in cost.

In practice, in large plants, with alternating-current machines it has become usual to mount the field magnets on the shaft, and build the armature as a stationary ring in whose air s.p.a.ce the field coils revolve. This simplifies the construction of slow-speed, large-output dynamos. Such a machine, however, is not to be had for the modest isolated plant of the farmer with his small water-power.

[Ill.u.s.tration: Instantaneous photograph of high-pressure water jet being quenched by buckets of a tangential wheel]

[Ill.u.s.tration: A tangential wheel, and a dynamo keyed to the same shaft--the ideal method for generating electricity. The centrifugal governor is included on the same base]

Dynamos can be designed for almost any waterwheel speed, and, among small manufacturers especially, there is a disposition to furnish these special machines at little advance in price over their stock machines. Frequently it is merely a matter of changing the winding on a stock machine. The farmer himself, in many cases, can re-wind an old dynamo to fit the speed requirements of a direct-connected drive if the difference is not too great. All that would be necessary to effect this change would be to get the necessary winding data from the manufacturer himself, and proceed with the winding. This data would give the gauge of wire and the number of turns required for each spool of the field magnets; and the gauge of wire and number of turns required for each slot in the armature. The average boy who has studied electricity (and there is something about electricity that makes it closer to the boy's heart than his pet dog) could do this work. The advantages of direct drive are so many that it should be used wherever possible.

When direct drive cannot be had, a belt must be used, either from a main shaft, or a countershaft. The belt must be of liberal size, and must be of the "endless" variety--with a scarfed joint. Leather belt lacing, or even the better grades of wire lacing, unless very carefully used, will prove unsatisfactory. The dynamo feels every variation in speed, and this is reflected in the lights. There is nothing quite so annoying as flickering lights. Usually this can be traced to the belt connections. Leather lacing forms a knot which causes the lights to flicker at each revolution of the belt. The endless belt does away with this trouble. Most dynamos are provided with sliding bases, by which the machine can be moved one way or another a few inches, to take up slack in the belt. To take advantage of this, the belt must be run in a horizontal line, or nearly so.

Vertical belting is to be avoided.

The dynamo is mounted on a wooden base, in a dry location where it is protected from the weather, or dampness from any source. It must be mounted firmly, to prevent vibration when running up to speed; and the switchboard should occupy a place within easy reach. Wires running from the dynamo to the switchboard should be protected from injury, and must be of ample size to carry the full current of the machine without heating. A neat way is to carry them down through the flooring through porcelain tubes, thence to a point where they can be brought up at the back of the switchboard. If there is any danger of injury to these mains they may be enclosed in iron pipe. Keep the wires out of sight as much as possible, and make all connections on the back of the switchboard.

_The Switchboard_

[Ill.u.s.tration: Connecting switchboard instruments]

The switchboard is constructed of some fireproof material, preferably slate or marble. When the cost of this material is an item to consider, build a substantial wooden frame for your switchboard. You can then screw asbestos s.h.i.+ngles to this to hold the various instruments and with a little care such a switchboard can be made to look business-like, and it is fully as serviceable as the more expensive kind. The switchboard instruments have already been described briefly. They consist of a voltmeter (to measure voltage); an ammeter (to measure the strength of the current drawn, in amperes), a rheostat (to regulate the voltage of the machine to suit the individual requirements); and the usual switches and fuses. The main switch should be so wired that when open it will throw all the current off the line, but still leave the field coils, the voltmeter, and the switchboard lamp in circuit. The main-switch fuses should have a capacity about 50 per cent in excess of the full load of the dynamo.

If the machine is rated for 50 amperes, 75-ampere fuses should be installed. This permits throwing on an overload in an emergency; and at the same time guards against a short circuit. If the capacity of the machine is under 30 amperes, plug fuses, costing 3 cents each, can be used. If it is above this capacity, cartridge fuses, costing a little more, are required. A supply of these fuses should be kept handy at all times.

_Governors and Voltage Regulators_

[Ill.u.s.tration: A centrifugal governor (Courtesy of the C. P. Bradway Company, West Stafford, Conn.)]

The necessity for water wheel governors will vary with conditions. As a general rule, it may be said that reaction turbines working under a low head with a large quant.i.ty of water do not require as much governing as the impulse wheel, working under high heads with small quant.i.ties of water. When governing is necessary at all, it is because the prime mover varies in speed from no load to full load. Planning one's plant with a liberal allowance of power--two water horsepower to one electrical horsepower is liberal--reduces the necessity of governors to a minimum. As an instance of this, the plant described in some detail in Chapters One and Six of this volume, runs without a governor.

However, a surplus of water-power is not usual. Generally plants are designed within narrow limits; and then the need of a governor becomes immediately apparent. There are many designs of governors on the market, the cheapest being of the centrifugal type, in which a pair of whirling b.a.l.l.s are connected to the water wheel gate by means of gears, and open or close the gate as the speed lowers or rises.

Constant speed is necessary because voltage is directly dependent on speed. If the speed falls 25 per cent, the voltage falls likewise; and a plant with the voltage varying between such limits would be a constant source of annoyance, as well as expense for burned-out lamps.

Since constant voltage is the result aimed at by the use of a governor, the same result can be attained in other ways, several of which will be explained here briefly.

_Over-Compounding_

(1) Over-compounding the dynamo. This is simple and cheap, if one buys the right dynamo in the first instance; or if he can do the over-compounding himself, by the method described in the concluding paragraphs of Chapter Seven. If it is found that the speed of the water wheel drops 25 per cent between no load and full load, a dynamo with field coils over-compounded to this extent would give a fairly constant regulation. If you are buying a special dynamo for direct drive, your manufacturer can supply you with a machine that will maintain constant voltage under the normal variations in speed of your wheel.

_A System of Resistances_

(2) Constant load systems. This system provides that the dynamo shall be delivering a fixed amount of current at all times, under which circ.u.mstances the water wheel would not require regulation, as the demands on it would not vary from minute to minute or hour to hour.