Fig. 1,008.—Wiring for heating appliances; plan of second floor.
The location of the outlets for the heating appliances is not of the least importance. For many purposes, the flush receptacle in the baseboard of the room answers many requirements. In other places, for instance, a receptacle placed beneath the bracket lamp in the bathroom upon the same circuit as the lamp, is very convenient as a connection for the electric shaving mug or the massage motor. Similarly, a suitable outlet placed near the head of the bed is most convenient for operating a heating pad as it does not necessitate unscrewing a lamp at night.
The house illustrated in figs. 1,006 to 1,008 is an example of the use of a single electric heating circuit with a restricted use of the lighting circuit for heating purposes.
Fig. 1,009.—Diagram illustrating wiring with combination of moulding, flexible tubing or conduit in non-fireproof building, where wiring had not been originally installed. In such cases the moulding may be run in a cornice in the hall. When objectionable to have the work exposed in the rooms, taps may be made in the moulding opposite each room and the circuit extensions from the moulding to the center outlets in the rooms may be run in flexible conduit, fishing the wires from the moulding to the ceiling outlet. The use of wooden moulding in new buildings is not to be recommended for the reason that it is not usually fireproof, and it would be better to run the conductors concealed in some form of conduit; if the circuit work were installed at the time the building is erected, it would cost but little more than moulding, and would be much more substantial. In some cases, however, wooden moulding might be provided in a new building on the ceiling as a means of affording facilities for making connections to outlets over desks, tables, etc., where it would be impossible to locate the outlet exactly before the building was plastered. In such cases, the moulding could be installed on the ceiling at a distance of 18 to 24 inches from the walls, forming a rectangle on the ceiling.
Fig. 1,010.—Feeder system for large hotel. The cellar, basement, and ground floors are supplied by separate feeders, because of the importance of having continuous and uninterrupted lighting service at these floors. The three distributing centers at the cellar are supplied by a single feeder. Three of the eight distributing centers at the basement floor serve to supply the outside lights, as described above. The distributing center for the outside street lamps is supplied by a separate feeder from the main switchboard. Five of the distributing centers at the basement floor serve for the basement lights only; they are fed by two separate feeders, one of which serves two centers and the other three centers as shown. Each of the three centers at the ground floor is supplied by a separate feeder. The upper floors, from the first to the fourteenth inclusive, are divided into two symmetrical sections. Each section has its own distributing center, and its own set of supply feeders. The feeder terminates at the middle center of a group of three, and is extended by mains to the corresponding centers at the floors immediately above and below. Each feeder from the first to the twelfth floor inclusive serves to supply three distributing centers.
As can be seen in the basement plan, the main supply circuit enters the basement and from this the heating circuit and lighting circuits branch, as shown by the arrows. The heating circuit runs direct to the basement laundry, a branch running to the flat iron. Connections are made with the kitchen on the first floor and with the dining room by branch circuits running through the partitions to the respective rooms. The heating circuit at the dining room is provided with flush wall receptacles, to which connection is made for the chafing dish and percolator.
In the kitchen the electric baking outfit is arranged as shown. This electric outfit is used for auxiliary cooking, such as a gas range would be, and the oven, placed by itself on the opposite side of the coal range, is controlled from the main table.
Upstairs the heating circuit, upon which the dining room appliances are operated, is extended to supply current to the electric luminous radiator, either in the chamber or bathroom.
The arrangements for the lighting circuits are shown in the figures. Landing and basement lights are controlled by three way switches to make them convenient.
In the living room a flush floor receptacle is installed so that the reading lamp, chafing dish or coffee percolator can be operated without necessitating the use of a long cord. A few of the electrical outlets suitable for the purposes mentioned are illustrated.
Where several heating circuits are used it is essential that an appliance taking a large current be not placed on the regular lighting circuit. To guard against this possibility, special receptacles should be installed, constructed for plugs which will not fit any other receptacle.
CHAPTER XLII
SIGN FLASHERS
The devices used for giving the flashing and changeable effects to electric lights in any form are called "flashers." The mechanism may be constructed to flash a sign by spelling the words out, one letter at a time, flashing border lights around a window, changing colors in glass signs, or in fact in any way to attract the eye.
There are two advantages in favor of using a flasher: 1, it causes the passerby to look at the sign, and 2, reduces the cost of electricity, because the lamps are switched off periodically.
There are numerous kinds of flasher, and they may be classified, according to construction of the switch contacts, as:
1. Carbon type;
2. Brush type;
3. Knife type.
Again, with respect to operation or the electrical effects, they may be classified as
1. Simple on and off flashers;
2. High speed flashers;
3. Lightning flashers;
4. Script breakers;
5. Chaser flashers;
6. Thermo flashers;
7. Carriage calls;
8. Talking signs;
9. Electric clocks.
Fig. 1,011—Dull's carbon type flasher. This is a main line flasher; that is, it is set into the main wires instead of carrying down each circuit. The circuits are opened and closed on carbon contacts, reinforced with standard knife switches. The blades are opened and the current broken by gravity alone. Each switch can be made to hold the lights for any period from 18% to 81% of a revolution of the shaft. They can throw on the circuits progressively or all on and all off together. Again, the circuits may be closed progressively, remain on a few seconds, and then be opened progressively. No circuit or circuits can be closed more than once per revolution.
Carbon Flashers.—In this type of flasher, carbon breaks are provided, that is, the arc which is formed when the circuit is broken, falls on carbon, while metal switches are provided to carry the load. Thus the carbon gets the arc which prevents the switches burning, while the switches carry the load to prevent the carbons becoming heated and disintegrated. The carbons must be adjusted occasionally according to the load they are carrying. Carbon machines are made either double, triple, or series break.
Figs. 1,012 to 1,014.—Wiring diagrams for Dull's carbon flashers. Fig. 1,012, usual method of wiring. The load is balanced by running the neutral wire around the machine, to the cut outs, breaking the outside "legs" only of a 220-110 volt system. While this method of wiring is entirely feasible, it is no harder on the contacts, and permits the use of a cheaper machine, but it is technically a violation of the underwriters' rules, which say that all circuits of more than 660 watts must be broken double pole. If the load be balanced there would be double pole break at 220 volts, and the lamps would be in series, but if the load be not exactly balanced, there would be single breaking to the extent of the amperes over the average balance. In other words, it is a double break and it is not according to circumstances, and the use of this machine wired as above is a matter that should be taken up with the local inspector before installing. Fig. 1.013, diagram for connecting a straight two wire carbon flasher on a two wire system. Fig. 1,014, diagram for connecting a straight three wire carbon flasher on a three wire system and breaking the neutral.
Fig. 1,015.—Reynolds' brush type flasher. The brush type, as its name indicates, is of brush construction and is limited to 5 amperes capacity on each switch. The cams constituting a drum are of heavy construction while the brushes are of fine copper several leaves thick. It is most commonly used for spelling signs, that is, for letter by letter flashing.
Fig. 1,016.—Reynolds' knife type of flasher with metal contacts. The construction is cheaper than the carbon type. It is mounted on a slate base, and is heavily built throughout. The switches are designed for 15 amperes capacity double break.
Brush Flashers.—These machines are provided with brush contacts. These bear on cams constituting a drum, and they are usually made of several strips of copper. Brush flashers are generally used for spelling out signs one letter at a time, or work of a similar nature.
Fig. 1,017—Sign flasher transmission gearing. The view shows an oil tight gear case with cover plate removed. The gears are equipped with ball bearings and run in graphite grease. By means of the worm gear the large speed reduction necessary between the flasher shaft and motor is obtained without a multiplicity of gear wheels.
Knife Flashers.—This type of construction is cheaper than the carbon type. The switches are of the knife type with metal contacts. One manufacturer states that it is not advisable to build knife flashers for more than 15 amperes per double pole switch, as they cannot be depended upon to break a greater load for any length of time.
Simple On and Off Flashers.—These are used for flashing whole signs or heavy loads on and off. A flasher of this type consists essentially of a revolving double pole switch with reducing gear and connection to a small motor for operating same.
Fig. 1,018.—Simple on and off double pole flasher for "all on" or "all off" sign flashing. The machine is furnished with any number of switches ranging from 5 amperes up.
The machine may have only one switch or any number of switches. The connection to motor may be by belt or chain, or the motor may be directly connected to the worm gear.
Flash System of Gas Lighting—This system for simultaneously lighting a large number of gas burners, is used in large halls, churches, theatres, etc. Two sparking points, each insulated one from the other and from the burner, are arranged at each burner, so that a spark between the points passes through the jet of gas and ignites it. A number of sparking points and the secondary of an induction coil are connected in series. When the circuit through the primary of the induction coil is closed, sufficient pressure is induced in the secondary to cause sparks to jump across every jet in the series. Since the voltage is high, the wires must be installed with great precaution. The wire should be enclosed in glass tubing wherever it comes within less than 1¼ in. from the gas piping, except where purposely grounded.
High Speed Flashers.—Machines of this type are used for giving what is generally known as high speed effects, such as fountains, water, steam, smoke and fire effects, whirling borders, revolving wheels and work of a similar nature.
Fig. 1,019.—Dull's high speed flasher. It is mounted on a slate base 12 inches wide, the length being governed by the size of the machine. Motion is given to the rotary switches through worm and belt gearing. Iron cams are used, the current being taken therefrom by six-leaf brushes, provided with stiffeners. The wiring for the machine is simple; 4 c.p. lamps can be run on one wire. A border or ornament containing 160 lamps requires 12 wires between the sign and flasher. The flasher is made in 4 switch sizes only, viz.: No. 4, 8, 12, 16, etc. This is due to the fact that there are three parts of light to one of darkness.
Lightning Flashers.—These machines are for giving the appearance of a streak of lightning going across a display. There is very little expense attached to their operation, because not more than two-thirds of the lamps are turned on at one time, and this number for only about one-sixth of the time, as compared with the sign burning steadily.
Lightning strokes can be utilized in various ways, either alone or with other advertising pieces. Alone they can be placed along a cornice, across the front of a building, up and down the corners leading to a doorway, etc. They can be used in the center of a sign with letters above and below. In this case, it is best to alternate the stroke with the letters, that is, flash the wording on and then off. As soon as it goes out, the stroke flies across in the darkness, then the wording comes up again, say six times a minute.
Fig. 1,020—Wiring diagram for flags. These may be wired for high speed flashers by gradually increasing the lamp centers between the vertical rows from the flag staff to the end.
Fig. 1,021.—Diagram showing method of wiring for high speed effects on single lines. This wiring diagram would be carried out the same in the case of a travelling border, whether it be straight or otherwise. In the case of a fountain, begin numbering each stream at the bottom and carry out the same scheme to the end of that stream. When several streams are parallel, all the lamps may be connected in a row the same as though they were an individual lamp. Care should be taken not to get more than twenty No. 1 lamps on a circuit. Among the effects that may be obtained are a revolving wheel, a column of flame, and a straight travelling border with part of the No. 1 lamps from each effect to the same No. 1 wire, carry it back to any No. 1 switch on the machine, and the effect will come out right. For instance, in a flame effect with sixteen No. 1 lamps, four No. 1 lamps could be taken in the straight border, and put on the same wire, and the effect would come out right. The spacings for high speed effects vary, according to the size of the sign. Travelling borders around an ordinary sign 3 x 10 feet should have their lamps spaced about six inches apart. In a fountain fifteen feet high, the lamps should be spaced about nine inches apart.
Fig. 1.022.—Method of wiring for a torch. This wiring diagram gives the correct method of wiring smoke, flames, steam, and water effects. It may be the flame in the top of a torch as here shown, liquid pouring out of a bottle, smoke rising from a cigar, or dust behind an automobile wheel. The only difference being in the direction each goes and the outline of the bank of lamps. Wire the lamps in unequal lines across; avoid any straight lines because it gives a mechanical effect which is not natural. If the effect be to rise, mark the lower row No. 1, the next row above No. 2, etc. Pick up all the No. 1 rows until there are twenty lamps, and attach them to No. 1 wire which will go back to any No. 1 switch on the machine. Do the same with the other numbers. Do not overload line as this will decrease the life of the contacts.
Figs. 1,023 and 1,024.—Wiring diagrams for high speeds. Where a high speed flasher is used on a spoked wheel containing more lamps in the rim than the number of spokes, the extra rim lamps must be connected to the spoke circuits, so that the number of rim circuits will equal the number of spokes; otherwise, the rim will appear to travel slower than the spokes.
In the case of a sign already in use, on the front of a building or over the sidewalk, a stroke can be placed leading to the sign from any point above. The flash goes down and when it hits the sign the latter lights up, holds a few seconds, goes out, and repeats about four times a minute.
Fig. 1,025—Dull's lightning type flasher for giving the appearance of a streak of lightning going across a display.
Lightning flashes are not usually constructed for heavy loads, the one shown in fig. 1,025 being designed for two amperes.
Script Breakers.—Flashers of this type are used for breaking large script signs, one socket at a time; that is, each lamp is lighted one after another until all are on. After a few seconds they all go out simultaneously and repeat. This gives the appearance of an invisible hand, writing the name in the darkness, and is very effective. The result can be accomplished only with script, and to get the proper effect the smallest letter in a sign should be not less than two feet high; the larger the letter, the better the effect.
Fig. 1,026.—Betts' script breaker (brush type). This flasher is especially designed for spelling out signs one letter at a time, or work of a similar nature, The brushes for the revolving cam contacts are of copper, several leaves thick and provided with special brush holder to prevent loose contact and abnormal burning.
Script breakers are also used for fancy border signs of other kinds, and in order to produce these results, it is necessary that the return wire of every lamp go back to the flashers independently, which means a wire for each lamp.
Chaser Flashers.—This class of flasher is designed to operate signs whose lamps are arranged to give the effect of snakes chasing each other around the border. This peculiar effect is produced by having a separate wire and a separate switch on the flasher for each two lamps in the border, and the mechanism so arranged that when the tenth lamp is lighted (assuming the snake to be ten lamps long) the first lamp goes out; when the eleventh is lighted, the second goes out, etc., progressing in this way around the entire border.
Fig. 1,027.—Reynolds chaser type of flasher, as used on electric signs whose lamps are arranged to give the effect of snakes chasing each other around the border of a sign.
In operation, the lamps are turned on and off so rapidly that it produces the effect of snakes.
It is not advisable to build these signs small nor cheaply, as in order to produce the desired effect, the curved path taken by the snake should cover at least 10 inches width, which would mean a total of 20 inches lateral space for the snake in addition to the electric letters in the center. In order to get the proper effect, the sign should be at least ten feet long.
Ques. Why are chaser signs expensive?
Ans. It is on account of the care required in their construction, large amount of wiring necessary and large flasher required.
A sign four by ten feet outside dimensions, would require in the neighborhood of 150 lamps in the border alone on each side. This would require a flasher with 75 switches and about 82 wires to run between the sign and flasher.
Fig. 1,028.—Chaser wiring diagram for two snakes. Draw a line diagonally through the sign (as shown in dotted line) so that one-half the total lamps will be on either side. Begin to number from one consecutively to the line. Over the line commence again at 1 and number as before. For three snakes, divide total lamps into three parts and number as before. In each case, connect all lamps of the same number to the same wire whether the sign be single or double face. The wire containing all the No. 1 lamps goes to the No. 1 switch on the flasher, and the remaining sets are connected similarly.
Ques. How are chaser signs worked?
Ans. There are several ways of operating these signs. The border is generally working continuously, while the center can be flashed or not, as may be desired. Flashing the wording reduces the current expense, which offsets in a measure the extra cost of the sign.
The border, although working continuously consumes very little current.
Ques. What is the relative cost of a one snake sign as compared with a two snake sign?
Ans. One snake running around the border would cost twice as much for flasher and wiring as a two snake flasher.
Three snakes would cost about 25 per cent. less for flasher and wiring than for two snakes. The smaller the number of snakes travelling around the border at one time, the greater the expense of wiring and flasher.
Fig. 1,029.—Thermo flasher. It consists of two metal strips, one of brass and the other of iron, about 5"x ½" x 1/32" each. The brass strip is provided with a winding of fine wire over asbestos and the two strips are connected to the base as shown. One terminal of the winding is connected to J, and the other end to M. At the end of the strips is a small contact screw N with locknut O, and below is a contact plate L, fastened to the base and terminal post R. The flasher is connected at P and R in series with the lamp it is to flash, and N adjusted so that it clears the plate about 1/32 inch when there is no current flowing in the winding. When the switch is turned on there will be a current through the lamp and winding in series. The brass strip will be heated more than the iron and it will expand more, thus forcing the point of the screw N down upon the brass plate, which will result in the winding about the brass strip being shorted and the full voltage will be impressed upon the lamp, and it will burn at normal candle power. When the coil is shorted there will of course be no current in its winding and the brass strip will cool down, the screw N will finally be drawn away from contact with the brass plate, and the winding again connected in series with the lamp. The lamp will apparently go out when the winding is in series with it, as the total resistance of the lamp and winding combined will not permit sufficient current to pass through the lamp to make its filament glow. The time the lamp is on and off may be varied to a certain extent by adjusting the screw N.
Ques. How many snakes should there be for best effect?
Ans. Two is considered best. Three may be used on some signs, but more than four would, in most cases, so crowd them as to spoil the effect entirely.
Thermo Flashers.—These flashers work on the thermo or heat expansion principle, that is, the movement of the contact points of the flasher necessary to open and close the circuit is obtained automatically by the alternate heating and cooling of the metal of the flasher, which causes it to expand and contract.
Fig. 1,030.—Thermal flasher. This simple flasher consists of a brass strip fixed at each end to a porcelain base and slightly arched upwards. The amount of this arching, however, is much less than is shown in the figure. The center of the strip carries a platinum contact on its upper surface, and opposite this is a platinum tipped contact screw which is carried in a brass angle piece fixed to the base. One terminal is fitted on one end of the strip, and the other is connected, through the angle piece, with the contact screw. The strip is wound from end to end with an insulated resistance wire, one end of this being soldered to the strip, and the other connected to the right hand terminal. When this device is switched into circuit with the lamps, the current first flows through the resistance, which cuts it down so much that the lamps are not visibly affected. The heat generated in the resistance causes the strip to curve still more, till at length contact is made, the resistance short circuited, and the lamps lighted.
Fig. 1,031.—General Electric thermal flasher. It consists of a small brass cylinder fixed at its left hand end to one of the terminal blocks. The junction between the two is hidden by a portion of the cover, which is shown broken away. The right hand end of the cylinder carries a cross piece bearing a platinum contact; and opposite this is the platinum tip of a contact screw carried in the other terminal block. The cylinder is wound with a heating coil of manganin resistance wire, one end being soldered to the cylinder and the other to the right hand terminal. When the current is switched on, the coil and the cylinder warm up and the cylinder elongates sufficiently to make contact and light the lamps. The coil being then short circuited, it and the cylinder cool down, and contact is broken, whereupon the coil is put in circuit once more, and warms up again. In some sizes of this flasher, the contact gap is shunted by a small condenser fitted beneath the base. This helps to eliminate the sparking at the contacts.
Carriage Calls.—These are used to avoid the confusion and noise at the theatre, club house or department store when vehicles are called by a megaphone.
Fig. 1,032.—Monogram or unit for carriage call or talking sign. It consists of a collection of metal compartments each arranged to receive an incandescent lamp. The purpose of these compartments is to confine the light to a certain space, thus forming a clearly defined number or letter which can be read from a distance.
Fig. 1,033 and 1,034.—Wiring diagrams showing proper methods of wiring for illuminating a painted sign. The lamps are placed about one foot apart in an overhead inverted trough. They should project out in front of the sign one-half its width, but no sign should be more than eight feet wide, as ordinary 16 c.p. lamps will not carry any farther. Black and white paint only should be used. The lamps may be flashed on and off as a whole, saving one-half the current, or they can be flashed in different colors as desired. For flashing in colors, only red and amber should be used. No other colors, such as green, blue, etc., will give sufficient light to produce a good effect.
The call itself consists of two or more sheet steel boxes, one of which is shown in fig. 1,032, with incandescent lamps arranged in metal compartments in such order that any number may be produced by lighting the proper lamps.
Fig. 1,035.—Operating keyboard for three number National carriage call. The keyboard here shown is designed to control a three number call, there being a row of keys for each monogram or unit of the call. Its dimensions are 4 inches deep, 18 inches wide and 19 inches long. The base is of slate. There are fourteen wires for each monogram and one return wire, coming out of the call.
The flashing of the number is controlled by a keyboard or switch which may be placed in any convenient location. When the switch and call are connected together, any numeral may be flashed by pressing the corresponding key. The numeral automatically remains lighted until the releasing button is pressed.
Fig. 1,036.—Clock monogram or electric sign clock, operated by the mechanism shown in fig. 1,037.
Fig. 1,037.—Betts' clock mechanism for operating electric monogram time flasher. The secondary mechanism consists of a three cylinder flasher and is controlled by a master clock which transmits an electric impulse through a relay switch one each minute. This flashes the time in figures on the monogram, viz.: 11.45, 11.46, 11.47, 11.48, etc. The first monogram to the left consists simply of a vertical row of lights representing the figure one. Each of the other monograms of metal compartments so arranged that any figure may be produced by lighting the proper combination of lamps.
Talking Signs.—This type of electric sign automatically flashes out in brilliant letters, different phrases or announcements. These are flashed out repeatedly and continuously during the operation of the sign and the changes follow each other without intermission of darkness.
Fig. 1,038.—Two way thermal flasher. The moving portion consists of a rocking arm A pivoted at p, and carrying two sealed bulbs, B, B', whose bottoms are united by the tube T. Inside there is sufficient mercury M to fill T and the bottoms of the bulbs, the remainder containing air. At each end of A is fixed an insulating block I, I', carrying two contact prongs P and P', which are connected together at the top through heater wires H, H' sealed in the bulbs B and B' respectively. MC, MC' are pairs of mercury cups, the further one of each pair whose stud is marked +, being connected together to the positive pole of the circuit, while the front ones are joined up to the respective groups of lamps. The action is as follows: If the apparatus be in the position illustrated, when the circuit is closed at the time P is down, lamp group No. 1 will light up, the current passing through H on its way. The air in B consequently expands, and gradually forces the mercury down in B, along T, and up in B'. The arm A will gradually become horizontal, and will then overbalance, P being withdrawn from MC, and P' dipped into MC'. Lamp group No. 1 will consequently be extinguished and lamp group No. 2 lighted; H will cool down, and H' will warm up. Thus, in due course, A will be tilted the other way again.
The talking sign consists of any desired number of monograms or units, in each of which any letter or figure can be formed by lighting certain combinations of incandescent lamps. A unit is shown in fig. 1,032. The lamps are controlled by a simple mechanical arrangement operated by a small motor. Any reading matter can be flashed by properly setting the mechanism.
The flashing of the letters or numerals in the monogram is controlled by commutators, one commutator being required for each monogram, except for a double faced sign where the corresponding monogram on each side is controlled by the same commutator.
CHAPTER XLIII
LIGHTNING PROTECTION
A lightning arrester is an apparatus designed to provide a path by which lightning disturbances or other static discharges may pass to earth. Lightning arresters may be divided into three classes, according as their action depends upon the effects of:
1. Sharp points;
2. Air gaps;
3. Sharp turns.
Lightning Rods.—This form of arrester consists of a conducting rod or cable erected on the outside of a building and connected to earth, in order to afford protection from lightning by carrying the lightning discharge into the ground; or to prevent lightning by leading the electricity from the earth to the cloud without disturbance.
Ques. Why do lightning rods terminate in sharp points?
Ans. The action of the rod depends on the discharging effect of a sharp point as follows: When an electrically charged cloud approaches a building provided with a lightning rod, it induces an opposite charge in the earth and in the rod which is connected to the earth. As soon as the charge on the point becomes strong enough to break apart the molecules of the air in front of it, a stream of electrified particles, opposite in sign to that of the charge on the cloud, passes from the neighborhood of the rod to the cloud and thus neutralizes the charge of the cloud.
Ques. How should a lightning rod be erected?
Ans. The conductor should be carried to all high points of the building it is to protect and should be well insulated from the latter and grounded in deep wet earth, independent of gas or water pipes. Sharp bends and corners should be avoided.
Fig. 1,039.—Diagram showing principle of air gap arrester: lightning discharges more readily at sharp points than along flat surfaces.
Ques. Why have lightning rods fallen into disfavor?
Ans. On account of numerous failures due to faulty installations, and non-maintenance of the rod in good condition, also because of the excessive prices charged by unscrupulous dealers for rods and their erection.
A lightning rod with defective insulation or broken ground connection is a danger rather than a protection.
Air Gap Arresters.—Many of the lightning arresters used for the protection of electrical apparatus depend upon the fact that lightning discharges will jump across air spaces that are good insulators for the regular working current, while they find difficulty in passing through circuits containing electromagnets.
Fig. 1,040.—Union lightning arrester and ground wire switch for telegraph lines. Two line wires are attached to the two plates provided with points. The ground wire being connected to the third or central plate. The pin serves as a ground wire switch and cut out. This is a good form for short lines.
The principle of air gap arresters is illustrated in fig. 1,039. There are two brass plates slightly separated; one is connected to the line and the other is grounded. The air gap between the plates is very small and the resistance thus interposed, while sufficient to prevent the regular working current jumping across, is not great enough to interfere with a lightning discharge which readily jumps the gap and passes off to earth.
Ques. Why are teeth provided on the plates?
Ans. For the same reason that points are used on lightning rods. That is, when electricity at high pressure accumulates at such points the surrounding air is electrified and the charge escapes by means of the charged air particles.
Fig. 1,041.—Mason multi-discharge lightning arrester. The construction of this arrester is based on the well known principle that lightning discharges more readily at points or angles than elsewhere. The wire is wound around square carbon rods, which are connected to the ground, the line being insulated from the rods by sheets of mica. The wire itself being square, instead of round, adds to the efficiency of the arrester, by increasing the number of points or angles.
Ques. For what kind of service is the form of arrester just described used?
Ans. It is suitable for telegraph and telephone lines where currents of very low voltage are employed.
Ques. Why is it not used on lines employing higher voltage, such as in electric light and power stations?
Ans. Current at high pressure would follow the lightning across the gap and establish an arc or continuous flame from one plate to the other thus quickly destroying the plates and causing other more serious damage.
Ques. What provision is made to prevent the destruction of arresters by the line current?
Ans. Lightning arresters used on heavy duty circuits are designed to rupture the arc as soon as formed.
Fig. 1,042.—Diagram showing operation of variable gap arc breaker used on heavy duty lightning arresters. When a lightning discharge passes across the gap to earth, the dynamo current follows it and energizes the magnet M, which attracts the short arm of the double lever, thus quickly jerking the terminal B away from C. The wider air gap thus interposed between B and C greatly increases the resistance which breaks the arc.
Ques. How is this done?
Ans. There are several methods, of which may be mentioned the variable gap method described in fig. 1,042, and the magnetic blow out method shown in fig. 1,043.
Ques. Where should lightning arresters be placed?
Ans. They should be placed as near as possible to the point where wires enter a building, and in an easily accessible place away from combustible material.
Ques. What should be avoided in installing lightning arresters?
Ans. Kinks and sharp bends in the wire running from the outdoor lines to the arresters and from arresters to ground should be avoided as far as possible.
Ques. Why should kinks and sharp bends be avoided?
Ans. Because they offer resistance to the lightning discharge.
Fig. 1,043.—Horn type lightning arrester. In this type of arrester, two wires, after approaching within a short distance of one another, are bent divergently. These wires are supported on insulators. One of them is connected to the line to be protected and the other is earthed. The normal line pressure is insufficient to bridge the gap, even at its narrowest portion, but an extra high pressure whether due to lightning or to other disturbing phenomena, will bridge the gap at its narrowest point and establish a path to earth. When, however, the main current attempts to flow across, phenomena of electromagnetic repulsion force the arc upward along the horns, lengthening and attenuating it, until it finally becomes extinguished.
Ques. How should lightning arresters be grounded?
Ans. They should be connected to ground with No. 6 B. & S. gauge copper wire or larger. Gas pipes within a building must not be used for a ground connection.
Fig. 1,044.—Ground connection for lightning arrester.
Fig. 1,045.—Carbon lightning arrester with fuses as used on telephone lines. The arrester consists of two blocks of carbon separated a small distance by a thin sheet of insulating mica, which is perforated with one or more holes; a high voltage charge on the line will jump through the hole in the mica from the carbon on the line side to the lower carbon, which is connected with the ground; the fuses protect the instruments against foreign currents which might damage, although not of sufficiently high pressure to jump to earth; sometimes the connections are reversed so that the fuse is between the line and the earth.
Ground connections may be made with a one inch galvanized iron pipe driven about 8 feet or until it reaches permanently moist earth, and extending at least 7 feet above ground. The ground wire should be securely soldered to a brass plug firmly screwed into the pipe, and both strongly stapled to the pole so there will be little danger of the connection being broken.
A good ground is important, as the efficiency of the protection would be impaired if the ground connection were poor. Wherever the earth is dry and a good ground cannot surely be obtained, an excavation 4 or 5 feet deep should be made, and after placing the copper ground plate or iron pipe in the hole, it should be filled with crushed coke or charcoal about pea size. This improves the electrical connection between pipe or plate and earth.
Ques. Does lightning often strike telephone or electric light lines?
Ans. No, the lines become charged to a high pressure by induction from lightning flashes or from the passing of clouds that are highly charged.
CHAPTER XLIV
STORAGE BATTERIES
Introduction.—The practical development of the storage battery is comparatively recent, although a knowledge of the phenomena upon which its actions are based, dates back to 1801. In 1800, the year made memorable by Volta's discovery of the galvanic battery, Nicholson and Carlisle found that a current from Volta's cell could decompose water.
In 1801, Gautherot discovered that if two plates of platinum or silver, immersed in a suitable electrolyte, be connected to the terminals of an active primary cell and current be allowed to flow, a small current could be obtained on an outside circuit connecting these two electrodes as soon as the primary battery had been disconnected.
Erman found that the positive pole of such a cell, was the pole which had been connected to the positive pole of the battery.
In 1803, Ritter observed, with gold wire, the same phenomenon as Gautherot, and constructed the first secondary battery, by superposing plates of gold, separated by cloth discs, moistened with ammonia.
Volta, Davy, Marianini, and others added somewhat to the knowledge on the subject, and in 1837, Schoenbein found that peroxide of lead could be used in secondary batteries.
Sir William Grove next came forward with the discovery that metal plates, with a layer of oxide on them, acted better than the plain metallic plates, and Wheatstone and Siemens found still later that peroxide of lead was the best for such purposes.
In 1842, Grove constructed a gas battery, in which the electromotive force came from the oxygen and hydrogen evolved in the electrolysis of water acidulated with sulphuric acid. By means of fifty such cells, he obtained an arc light.
Michael Faraday, when electrolyzing a solution of lead acetate, found that peroxide was produced at the positive, and metallic lead at the negative pole, and in his "Experimental Researches," he comments on the high conductivity of lead peroxide, and its power of readily giving up its oxygen. Although he made no apparent use of this discovery, it may be considered as the next important step in the development of the storage battery.
According to Niblett, Wheatstone, de la Rue, and Niaudet were well aware that peroxide of lead was a powerful depolarizer, but nobody appears to have made use of this fact until 1860, when M. Gaston Plante constructed his well known cell with coiled plates. Plante's researches extended up to 1879, and practically determined the state of the art.