Connections of shunt motor and starting rheostat
Just as there are three types of direct current generators, so there are three types of direct current motors:series,shunt, andcompound, with features already explained in the case of generators. Motors are rated by horsepower, and generators are rated by kilowatts. Thus a one kilowatt generator has a capacity of 1,000 watts; as a motor, it would be rated as 1000/746 horsepower, or 1.34 horsepower. Their efficiency varies with their size, ranging from 40 to 60 per cent in very small motors, and up to 95 per cent in very large ones. The following table may be taken as a guide in calculating the power required by motors, on 110-volt circuits:
An electric motor, in operation, actually generates electricity, which it pushes back into the line as a counter-electromotive-force. The strength of this counter force, in volts, depends on the motor's speed, the same as if it were running as a dynamo. For this reason, when a motor is started, and before it comes up to speed, there would be a rush of current from the line, with nothing to hold it back, and the motor would be burned out unless some means were provided to protect it for the moment. This is done by means of a starting rheostat, similar to the regulating rheostat on the dynamo switchboard. This resistance box is connected in "series" with the armature, in the case of shunt and compound motors; and with the entiremotor circuit in the case of a series machine.
Aseriesmotor has a powerful starting torque, and adjusts its speed to the load. It is used almost altogether in street cars. It can be used in stump pulling, or derrick work, such as using a hay fork. It must always be operated under load, otherwise, it would increase in speed until it tore itself to pieces through mechanical strain. The ingenious farmer who puts together an electric plow, with the mains following behind on a reel, will use a series motor.
Ashuntmotor should be used in all situations where a fairly uniform speed under load is required, such as separating, in milking machines, running a lathe, an ensilage cutter, vacuum cleaners, grinders, etc.
Thecompoundmotor has the characteristics of the series and shunt motors, giving an increased starting torque, and a more nearly constant speed under varying loads than the shunt motor, since the latter drops off slightly in speed with increasing load.
Flexible Power
An electric motor is an extremely satisfactory form of power because it is so flexible. Thus, one may use a five horsepower motor for a one horsepower task, and the motor will use only one electrical horsepower in current—just enough to overcome the task imposed on it. For this reason, a large-sized motor may be used for any operation, from one requiring small power, up to its full capacity. It will take an overload, the same as a dynamo. In other words it is "eager" for any task imposed on it; therefore it must be protected by fuses, or it will consume itself, if too big an overload is imposed on it.
A one horsepower shunt or compound motor is very serviceable for routine farm operations, such as operating the separator, the churn, the milking machine, grinder, pump, and other small power jobs. Motors of ¼ horsepower are handy in the kitchen, for grinding knives, polishing silver, etc., and can be used also for vacuum cleaners, and running the sewingmachine. For the larger operations, motors will vary from three horsepower for cutting ensilage, to fifteen horsepower for threshing. They can be mounted on trucks and conveyed from one point to another, being fed current from the mains by means of suitable wires wound on reels.
Remember, in estimating the size of your plant for light, heat, and power, that it does not have to be big enough to use all the devices at one time. Also remember, that two water horsepower to one electrical horsepower is a very liberal allowance; and that a generator working under one-half or two-thirds capacity at normal loads will require less attention than a machine constantly being worked above its capacity. Therefore, let your generator be of liberal size, because the difference in cost between a 5 and 10 kilowatt machine is not in proportion to their capacity. In fact (especially among second-hand machines), the difference in cost is very small. The mere fact that the generator is of 110 electrical horsepower capacity does not requirea turbine of 20 horsepower. The chances are that (unless you wish to heat your house and do large power jobs) you will not use more than 3 to 5 electrical horsepower normally; therefore an allowance of 10 water horsepower, in this case, would be ample. A plant used simply for lighting the house and barn, for irons, and toasters, and one horsepower motors, need not exceed 2 or 2½ kilowatts for the generator, and 5 or 6 horsepower for the turbine wheel. Normally it would not use one-half this capacity.
TRANSMISSION LINES
Copper wire—Setting of poles—Loss of power in transmission—Ohm's Law and examples of how it is used in figuring size of wire—Copper-wire tables—Examples of transmission lines—When to use high voltages—Over-compounding a dynamo to overcome transmission loss.
Copper wire—Setting of poles—Loss of power in transmission—Ohm's Law and examples of how it is used in figuring size of wire—Copper-wire tables—Examples of transmission lines—When to use high voltages—Over-compounding a dynamo to overcome transmission loss.
Having determined on the location of the farm water-power electric plant, and its capacity, in terms of electricity, there remains the wiring, for the transmission line, and the house and barn.
For transmission lines, copper wire covered with waterproof braid—the so-called weatherproof wire of the trade—is used. Under no circumstances should a wire smaller than No. 8, B. & S. gauge be used for this purpose, as it would not be strong enough mechanically. The poles should be of chestnut or cedar, 25 feet long, and set four feet in the ground. Where it is necessary to follow highways, theyshould be set on the fence line; and in crossing public highways, the ordinance of your own town must guide you. Some towns prescribe a height of 19 feet above the road, others 27 feet, some 30. Direct current, such as is advised for farm installations, under ordinary circumstances, does not affect telephone wires, and therefore transmission lines may be strung on telephone poles. Poles are set at an average distance of 8 rods; they are set inclined outward on corners. Sometimes it is necessary to brace them with guy wires or wooden braces. Glass insulators are used to fasten the wires to the cross-arms of the poles, and the tie-wires used for this purpose must be the same size as the main wire and carry the same insulation.
Size of Wire for Transmission
To determine the size of the transmission wires will require knowledge of the strength of current (in amperes) to be carried, and the distance in feet. In transmission, the electric current is again analogous to water flowing inpipes. It is subject to resistance, which cuts down the amount of current (in watts) delivered.
Bringing wires into the house or barn
The loss in transmission is primarily measured in volts; and since the capacity of an electric current for work equals thevoltsmultiplied byamperes, which giveswatts, every volt lost reduces the working capacity of the current by so much. This loss is referred to by electrical engineers as the "C^2R loss," which is another way of saying that the loss is equal to thesquare of the current in amperes, multiplied byohmsresistance. Thus, if theamperes carried is 10, and the ohms resistance of the line is 5, then the loss in watts to convey that current would be (10 × 10) × 5, or 500 watts, nearly a horsepower.
The pressure ofone volt(as we have seen in another chapter) is sufficient to forceone ampere, through a resistance ofone ohm. Such a current would have no capacity for work, since its pressure would be consumed in the mere act of transmission.
If, however, the pressure were110 volts, and the currentone ampere, and the resistanceone ohm, the effective pressure after transmission would be 110-1, or 109 volts.
To force a 110-volt current of50 amperesthrough the resistance ofone ohm, would require the expenditure of50 voltspressure. Its capacity for work, after transmission, would be 110-50, or60 volts, × 50 amperes, or 3,000 watts. As this current consisted of110 × 50, or 5,500 watts at the point of starting, the loss would be 2,500 watts, or about 45 per cent. It is bad engineering to allow more than 10 per cent loss in transmission.
There are two ways of keeping this loss down. One is by increasing the size of the transmission wires, thus cutting down the resistance in ohms; the other way is by raising the voltage, thus cutting down the per cent loss. For instance, suppose the pressure was 1,100 volts, instead of 110 volts. Five amperes at 1,100 volts pressure, gives the same number of watts, power, as 50 amperes, at 110 volts pressure. Therefore it would be necessary to carry only 5 amperes, at this rate. The loss would be 5 volts, or less than ½ of 1 per cent, as compared with 45 per cent with 110 volts.
Splicing transmission wire
In large generating stations, where individual dynamos frequently generate as much as 20,000 horsepower, and the current must be transmitted over several hundred miles of territory, the voltage is frequently as high as 150,000, with the amperes reduced in proportion. Then the voltage is lowered to a suitable rate, and the amperage raised in proportion, by special machinery, at the point of use.
It is the principle of the C^2R loss, which thefarmer must apply in determining the size of wire he is to use in transmitting his current from the generator switchboard to his house or barn. The wire table on page 159, together with the formula to be used in connection with it, reduce the calculations necessary to simple arithmetic. In this table the resistance of the various sizes of wire is computed from the fact that a wire of pure copper 1 foot long, and 1/1000 inch in diameter (equal to one circular mill) offers a resistance of 10.6 ohms to the foot. The principle of the C^2R loss is founded on Ohm's Law, which is explained in Chapter V.
The formula by which the size of transmission wire is determined, for any given distance, and a given number of amperes, is as follows:
(Distance ft. one way × 22 × No. of amperes) / (Number of volts lost) = circular mills.
In other words, multiply thedistance in feetfrom mill to house by 22, and multiply this product by thenumber of amperesto becarried. Then divide the product by thenumber of voltsto be lost; and the result will be the diameter of the wire requiredin circular mills. By referring to the table above, the B. & S. gauge of the wire necessary for transmission, can be found from the nearest corresponding number under the second column, entitled "circular mills area."
COPPER WIRE TABLE
CARRYING CAPACITY OF WIRES AND WEIGHT
Since two wires are required for electrical transmission, the above formula is made simple by counting the distance only one way, in feet, and doubling the resistance constant, 10.6, which, for convenience is taken as 22, instead of 21.2.
Examples of Transmission Lines
As an example, let us say that Farmer Jones has installed a water-power electric plant on his brook,200 yards distantfrom his house. The generator is a 5 kilowatt machine, capable of producing45 amperesat110 volts pressure. He has a 3 horsepower motor, drawing 26 amperes at full load; he has 20 lights of varying capacities, requiring1,200 watts, or 10 amperes when all on; and his wife uses irons, toasters, etc., which amount to another 9 or 10 amperes—say 45 altogether. The chances are that he will never use all of the apparatus at one time; but for flexibility, and his own satisfaction in not having to stop to think if he is overloading his wires, he would like to be able to draw the full45 amperesif he wishes to. He is willing to allow5 per cent lossin transmission.What size wires will be necessary, and what will they cost?Substituting these values in the above formula, the result is:
Answer: (600 × 22 × 45) / 5.5 = 108,000 circular mills.
Transmission wire on glass insulator
Referring to the table, No. 0 wire is 105,534 circular mills, and is near enough; so this wire would be used. It would require 1,200 feet,which would weigh, by the second table, 435.6 pounds. At 19 cents a pound, it would cost $82.76.
Farmer Jones says this is more money than he cares to spend for transmission. As a matter of fact, he says, he never uses his motor except in the daytime, when his lights are not burning; so the maximum load on his line at any one time would be26 amperes, not 45.What size wire would he use in this instance?
Substituting 26 for 45 in the equation, the result is 61,300 circular mills, which corresponds to No. 2 wire. It would cost $57.00.
Now, if Farmer Jones, in an emergency, wished to use his motor at the same time he was using all his lights and his wife was ironing and making toast—in other words, if he wanted to use the45 amperescapacity of his dynamo,how many volts would he lose?To get this answer, we change the formula about, until it reads as follows:
(Distance in feet × 22 × amperes) / circular mills = Number of volts lost
Substituting values, we have, in this case,
(600 × 22 × 45) / 66,373 (No. 2) = 9 volts,
nearly, less than 10 per cent. This is a very efficient line, under the circumstances. Now if he is willing to lose 10 per cent onhalf-load, instead of full load, he can save still more money in line wire. In that case (as you can find by applying the formula again), he could use No. 5 wire, at a cost of $28.50. He would lose 11 volts pressure drawing 26 amperes; and he would lose 18 volts pressure drawing 45 amperes, if by any chance he wished to use full load.
In actual practice, this dynamo would be regulated, by means of the field resistance, to register 110 plus 11 volts, or 121 volts at the switchboard to make up for the loss at half-load. At full load, his voltage at the end of the line would be 121 minus 18, or 103 volts; his motor would run a shade slower, at this voltage, and his lights would be slightly dimmer. He would probably not notice the difference. If he did, he could walk over to his generating station, and raisethe voltage a further 7 volts by turning the rheostat handle another notch.
A barn-yard light
Thousands of plants can be located within 100 feet of the house. If Farmer Jones could do this, he could use No. 8 wire, costing $2.62. The drop in pressure would be 5.99 volts at full load—so small it could be ignored entirely. In this case the voltmeter should be made to read 116 volts at the switchboard, by means of the rheostat.
If, on the other hand, this plant were 1,000 feet away from the house and the loss 10 volts the size wire would be
(1,000 × 22 × 45) / 10 = 99,000 circular mills;
a No. 0 wire comes nearest to this figure, and its cost, for 2,000 feet, at 19 cents a pound, would be $137.94.A No. 0000 wire, costing $294.00, would give a 5 per cent drop at full load. In this case, the cost of transmission can be reduced to a much lower figure, by allowing a bigger drop at half-load, with regulation at the switchboard. Thus, a No. 2 wire here, costing but $95, would be satisfactory in every way. The loss at half-load would be about 9 volts, and the rheostat would be set permanently for 119 or 120 volts. A modern dynamo can be regulated in voltage by over 25 per cent in either direction, without harm, if care is taken not to overload it.
Benefit of Higher Voltages
If Farmer Jones' plant is a half of a mile away from the house, he faces a more serious proposition in the way of transmission. Say he wishes to transmit 26 amperes with a loss of 10 volts. What size wire will be necessary?
Thus: (2640 × 22 × 26) / 10 = 151,000 circular mills.
A No. 000 wire is nearest this size, and 5,280 feet of it would cost over $650.00. This costwould be prohibitive. If, however, he installed a 220-volt dynamo—at no increase in cost—then he would have to transmit only a half of 26 amperes, or 13 amperes, and he could allow 22 volts loss, counting 10 per cent. In this case, the problem would work out as follows:
(2640 × 22 × 13) / 22 = 34,320 circular mills,
or approximately a No. 5 wire which, at 19 cents a pound, would cost $120.65.
Install a 550-volt generator, instead of a 220-volt machine and the amperes necessary would be cut to 5.2, and the volts lost would be raised to 55. In this case a No. 12 wire would carry the current; but since it would not be strong enough for stringing on poles, a No. 8 wire would be used, costing about $63.
It will be readily seen from these examples how voltage influences the efficiency of transmission. Current generated at a pressure in excess of 550 volts is not to be recommended for farm plants unless an expert is in charge.A safer rule is not to exceed 220 volts, for while 550 volts is not necessarily deadly, it is dangerous. When one goes into higher voltages, it is necessary to change the type of dynamo toalternating current, so that the current can be transformed to safe voltages at the point where it is used. Since only the occasional farm plant requires a high-tension system, the details of such a plant will not be gone into here.
In transmitting the electric current over miles of territory, engineers are accustomed to figure 1,000 volts for each mile. Since this is a deadly pressure, it should not be handled by any one not an expert, which, in this case, the farmer is not.
Over-Compounding the Generator
One can absorb the loss in transmission frequently, by over-compounding the machine. In describing the compound machine, in Chapter Five, it is shown that the usual compound dynamo on the market is the so-called flat-compounded type. In such a dynamo, thevoltage remains constant at the switchboard, from no load to full load, allowing for a slight curve which need not be taken into account.
Now, by adding a few more turns to the series wires on the field coils of such a dynamo, a machine is to be had which gradually raises its voltage as the load comes on in increasing volume. Thus, one could secure such a machine, which would begin generating at 110 volts, and would gradually rise to 150 at full load. Yet the voltage would remain constant at the point of use, the excess being absorbed in transmission. A machine of this type can be made to respond to any required rise in voltage.
As an example of how to take advantage of this very valuable fact, let us take an instance:
Say that Farmer Jones has a transmission line 1,000 feet long strung with No. 7 copper wire. This 2,000 feet of wire would introduce a resistance of one ohm in the circuit. That is, every ampere of current drawn at his house would cause the working voltage there to fallone volt. If he drew 26 amperes, the voltage would fall, at the house, 26 volts. If his switchboard voltage was set at say 120, the voltage at his house, at 26 amperes of load, would fall to 94 volts, which would cause his lights to dim considerably. It would be a very unsatisfactory transmission line, with a flat-compounded dynamo.
On the other hand, if his dynamo was over-compounded 25 per cent—that is, if it gained 28 volts from no load to full load, the system would be perfect. In this case, the dynamo would be operated at 110 volts pressure at the switchboard with no load. At full load the voltmeter would indicate 110 plus 26, or 136 volts. The one or two lights burned at the power plant would be subject to a severe strain; but the 50 or 100 lights burned at the house and barn would burn at constant voltage, which is very economical for lamps.
The task of over-compounding a dynamo can be done by any trained electrician. The farmer himself, if he progresses far enough in his study of electricity, can do it. It is necessaryto remove the top or "series" winding from the field coils. Count the number of turns of this wire to each spool. Then procure some identical wire in town and begin experimenting. Say you found four turns of field wire to each spool. Now wind on five, or six, being careful to wind it in the same direction as the coils you removed and connect it in the same way. If this additional number of turns does not raise the voltage enough, in actual practice, when the dynamo is running from no load to full load, add another turn or two. With patience, the task can be done by any careful mechanic. The danger is in not winding the coils the same way as before, and getting the connections wrong. To prevent this mistake, make a chart of the "series" coils as you take them off.
To make the task of over-compounding your own dynamo even more simple, write to the manufacturers, giving style and factory number of your machine. Tell them how much voltage rise you wish to secure, and ask them how many turns of "series" wire shouldbe wound on each spool in place of the old "series" coil. They could tell you exactly, since they have mathematical diagrams of each machine they make.
Avoid overloading an over-compounded machine. Since its voltage is raised automatically, its output in watts is increased a similar amount at the switchboard, and, for a given resistance, its output in amperes would be increased the same amount, as can be ascertained by applying Ohm's Law. Your ammeter is the best guide. Your machine is built to stand a certain number of amperes, and this should not be exceeded in general practice.
WIRING THE HOUSE
The insurance code—Different kinds of wiring described—Wooden moulding cheap and effective—The distributing panel—Branch circuits—Protecting the circuits—The use of porcelain tubes and other insulating devices—Putting up chandeliers and wall brackets—"Multiple" connections—How to connect a wall switch—Special wiring required for heat and power circuits—Knob and cleat wiring, its advantages and drawbacks.
The insurance code—Different kinds of wiring described—Wooden moulding cheap and effective—The distributing panel—Branch circuits—Protecting the circuits—The use of porcelain tubes and other insulating devices—Putting up chandeliers and wall brackets—"Multiple" connections—How to connect a wall switch—Special wiring required for heat and power circuits—Knob and cleat wiring, its advantages and drawbacks.
The task of wiring your house is a simple one, with well-defined rules prescribed by your insurance company. Electricity, properly installed, is much safer than oil lamps—so much so indeed that insurance companies are ready to quote especial rates. But they require that the wiring be done in accordance with rules laid down by their experts, who form a powerful organization known as the National Board of Fire Underwriters. Ask your insurance agent for a copy of the code rules.
Danger of fire from an electric current comes from the "short circuit," partial or complete; and it is against this danger that the rules guard one. The amount of electricity flowing through a short circuit is limited only by the fuse protecting that line; and since there is no substance known that can withstand the heat of the electric arc, short circuits must be guarded against. Happily the current is so easily controlled that the fire hazard is eliminated entirely—something which cannot be done with oil lamps.
In house-wiring for farm plants, the wire should be rubber-covered, and not smaller than No. 14 B. & S. gauge. This is the wire to use on all lamp circuits. It costs about $0.85 cents per 100 feet. There are four kinds of wiring permitted, under the insurance code:
(1)Flexible armoured cable: This consists of two-wire cable, protected with a covering of flexible steel. It is installed out of sight between the walls, and provides suitable outlets for lamps, etc., by means of metal boxesset flush with the plaster. It is easily installed in a house being built, but requires much tearing down of plaster for an old house. Since its expense prohibits it in the average farm house, this system will not be described in detail here.
(2)Rigid and flexible conduit: As the name implies this system consists of iron pipe, in connection with flexible conduit, run between the walls. It differs from the above system, in that the pipes with their fittings and outlet boxes are installed first, and the wires are then "fished" through them. Duplex wires—the two wires of the circuit woven in one braid—are used; and a liberal amount of soapstone, and occasionally kerosene, are used to make the wires slip easily into place. This is the most expensive system, and the best; but it is difficult to install it in an old house without tearing down a good deal of plaster. It has the advantage of being absolutely waterproof and fireproof.
(3)Wooden moulding: This is simply moulding, providing two raceways for the insulated wires to run in, and covered with a capping. It is nailed or screwed firmly to the wall, on top of the plaster; and when the wires have been installed in their respective slots and the capping tacked on, the moulding is given a coat of paint to make it in harmony with the other moulding in the room. This system is cheap, safe, and easily installed, and will be described in detail here.
Detail of wooden moulding
(4)Open wiring: In open wiring, the wires are stretched from one support to another (such as beams) and held by means of porcelain cleats, or knobs. It is the simplest to install; but it has the objection of leaving the wires unprotected, and is ugly. It is very satisfactory in barns or out-buildings however.
The Distributing Panel
The first point to consider in wiring a house with wooden moulding is the distribution board. It should be located centrally, on the wall near the ceiling, so as to be out of ordinary reach. It consists of a panel of wood—though fireproof material is better—firmly screwed to the wall, and containing in a row, the porcelain cut-outs, as shown in the cut, from which the various branch circuits are to be led. Each cut-out provides for two branch circuits; and each branch contains receptacles for two plug fuses. These fuses should be of 6 amperes each. The Insurance Code limits the amount of electricity that may be drawn on any branch lamp circuit to 660 watts; and these fuses protect the circuit from drafts beyond this amount.
Porcelain cut-out and plug fuse
The mains, leading from the entrance switch, as shown in the diagram, to the panelboard, should be of the same size as the transmission wire itself, and rubber-covered. These mains terminate at the distributing board. They are connected to the terminals of the cut-outs by means of heavy brass screws.
Wire Joints
Examples of cleat and knob wiring, 1, 2, 3; wire joints, 4; flexible armoured conductor, 5
The branch circuits are, as has been said, of No. 14 rubber-covered wire, running concealed in wooden moulding. All joints or splices in this wire are made, as shown in the illustration, by first scraping the wires bright, and fastening them stoutly together. This joint is then soldered, to make the connection electrically perfect. Soft solder is used, withordinary soldering salts. There are several compounds on the market, consisting of soft solder in powder form, ready-mixed with flux. Coat the wire joint with this paste and apply the flame of an alcohol lamp. The soldered joint is then covered with rubber tape, and over this ordinary friction tape is wound on. A neat joint should not be larger than the diameter of the wire before insulation is removed.
Branch Circuits
First, make a diagram of your rooms and indicate where you wish lamps, or outlets for other purposes. Since wooden moulding can be run across ceilings, and up or down walls, lamps may be located in places where they are out of the way. In planning the circuit, remember that you will want many outlets in handy places on the walls, from which portable cords will convey current to table lamps, to electric irons and toasters and other handy devices which can be used on the lamp circuit. These outlets are made of porcelain,in two pieces. One piece is merely a continuation of the moulding itself; and the other is a cap to connect permanently to the end of the lamp or iron cord, which may be snapped into place in a second. Since there are a great many designs of separable current taps on the market, it is well to select one design and stick to it throughout the house, so that any device can be connected to any outlet.
The code permits 660 watts on each circuit. This would allow 12 lamps of 55 watts each. It is well to limit any one circuit to 6 lamps; this will give leeway for the use of small stoves, irons, toasters, etc. without overloading the circuit and causing a fuse to blow.
Having installed your distributing board, with its cut-outs, figure out the course of your first branch circuit. Let us say it will provide lights and outlets for the dining room and living room. It will be necessary to run the wires through the partitions or floors in several places. For this purpose porcelain tubes should be used, costing one to three cents each. Knock holes in the plaster at the determinedpoint, insert the tubes so they project ¾ inch on each side, and fill up the ragged edge of the hole neatly with plaster.
The distributing panel
When all the tubes have been set in place, begin laying the moulding. Run it in a straight line, on the wall against the ceiling wherever possible, mitering the joints neatly. Whenever it is necessary to change the run from the ceiling to the wall and a miter cannot be made, the wires should be protected inpassing from one slot to the other by being enclosed in non-metallic flexible conduit, called circular loom.
In running wooden moulding, avoid brick walls liable to sweat or draw dampness; keep away from places where the heat of a stove might destroy the rubber insulation of the wires; do not pass nearer than six inches to water pipes when possible—and when it is necessary to pass nearer than this, the wooden moulding should pass above the pipe, not below it, with at least an inch of air space intervening, thus avoiding dampness from sweating of pipes.
Snap switch connections
Places where chandeliers or wall bracket lamps are to be installed permanently are fitted with wooden terminal blocks, which fitover the moulding and flush with the plaster. These, after holes have been bored in them for the wires, and the wires drawn through, should be screwed firmly to the wall or ceiling, always choosing a joist or beam for support. Then a crow's-foot, or tripod of iron, tapped and threaded for iron pipe, is screwed to the terminal block. The iron pipe of the chandelier or wall bracket is then screwed home in this crow's-foot.
Detail of wooden moulding
Do not begin stringing wires until all the moulding of the circuit has been laid. Then thread the wires through the wall or floor tubes and lay them in their respective slots. If trouble be found making them stay in place before the capping is put on, small tacks may be driven into the moulding beside them to hold them. When a terminal block is reached, a loop is made of each wire, through the hole cut in the block, if the circuit is to continue in the same direction. If it is to end there, the two wires are drawn through taut, and cut off at a length of 5 or 6 inches. These end wires, or loops, are then scraped bare andspliced to the two wires coming out of the chandelier or wall bracket. This joint is then soldered and covered with tape, and the shell of the chandelier is screwed into place, covering the joint.
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 brass screws.
"Multiple" Connections
All electric devices for this installation—lamps, irons, vacuum cleaners, motors—must be connectedacrossthe circuit—that is, bridged, from one wire to the other. This is calledmultiple, 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 wallswitch, 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 cluster, 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., asingle 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 1½ cents a foot; while a tin shade will cost another 15 cents.