CHAPTER VII ELECTRICAL APPURTENANCESWiresElectric currents are usually led from place to place, at will, by means of conductors calledwires. There are a great many kinds of wires, each adapted to some special purpose.Wires are usually covered with a material called aninsulator, in order to prevent the loss of electric current due to the wires coming into contact with other bodies or circuits. Insulators are substances which do not conduct electricity.Wires which areinsulatedby heavy braids of cotton fiber and then impregnated with some compound, such as creosote, are calledweather-proofwires, and are best adapted to outside service, where they must be exposed to the action of the elements.The wires used for interior wiring in buildings, etc., are usually insulated with rubber, over which is placed a cotton braid to protect the rubber.Rubber cannot well be used as an insulator for all wires, although its insulating value is very great, owing to the fact that it deteriorates under many conditions.Rubber-covered and weather-proof wires are made in a variety of insulations. Some may have only one insulating layer, while others have a great many. Different substances are used as insulators to adapt the wire to some special purpose. Copper is usually the only metal used to form the wire or conductor itself. The reason for this is that copper is a better conductor than any other metal except those known as precious metals, such as gold and silver, the cost of which prohibits their use for such purposes. The wire may be solid, or made up of a number of small conductors so that it is flexible.The various combinations of insulating layers, together with either a solid or a stranded conductor, have made possible a variety of current-carriers, known as:Theater or Stage CableElevator CableFixture WireTelephone WireMining CableFeeder CableBrewery CordHeater Cord, etc.depending upon the special use for which they were designed.NUMBER, DIAMETER, WEIGHT, LENGTH, AND RESISTANCE OF COPPER WIREThe wires which the young experimenter is likely to use in his work the most are known asmagnet wires, and are used for making electro-magnets, coils, and various windings. Magnet wires may be insulated with either silk, cotton, or enamel.NUMBER, DIAMETER, WEIGHT, LENGTH, AND RESISTANCE OF COPPER WIRESilk-covered and cotton-covered wires may be obtained with either a single or double covering.Wires with a single covering of silk or enamel are used when it is desirable to save space, for the covering of these two classes of magnet wires is thinner than either the cotton or double-silk-covered wire, and consequently they require less room for winding.The size of the wire is indicated by its diameter, and in the United States is measured by the Brown and Sharpe gauge, often indicated by the term, "B. & S."The preceding table shows the various sizes of wire of the Brown and Sharpe gauge, and also several of their characteristics, such as weight, resistance, etc.InsulatorsThe covering placed over wires is not the only precaution taken to insulate them, but in the case of permanent wiring they are usually mounted on glass or porcelain supports.Fig. 89.—Staples and Wooden Cleat used for running Low Voltage Wires.Fig. 89.—Staples and Wooden Cleat used for running Low Voltage Wires.Wires used for batteries, bells, telephones, etc., operated by batteries and where the voltage is not over 20 volts, may be run underinsulatedstaples or wooden cleats inside of a building. If outside and exposed to the weather, they should be mounted on suitable glass or porcelain knobs.Fig. 90.—Porcelain Insulators to support Electric Light Wires.Fig. 90.—Porcelain Insulators to support Electric Light Wires.Electric-light wires for inside use are commonly supported by insulators made of porcelain and known as cleats, knobs, and tubes according to the shape.Telegraph, telephone, and power lines are usually supported by glass knobs or large porcelain insulators which screw on to wooden pins.Fig. 91.—Glass Insulator Binding-Posts and Pin used to support Telegraph and Telephone wires.Fig. 91.—Glass Insulator Binding-Posts and Pin used to support Telegraph and Telephone wires.Binding-PostsBinding-posts are the most convenient device to make quick connections between wires and other parts of electrical apparatus.Binding-posts may be either made or purchased. Those which are purchased are of course the best, and will add greatly to the appearance of any instrument upon which they are mounted.Several of the best-known types of manufactured posts are shown in Figure 92.Fig. 92.—Types of Binding-Posts.Fig. 92.—Types of Binding-Posts.Figure 93 shows different ways of making simple binding-posts and connectors from screws, washers, screw-eyes, and strips of metal. The drawings are self-explanatory and should need no comment.Fig. 93.—Home-made Binding-Posts.Fig. 93.—Home-made Binding-Posts.The screws and nuts obtainable from old dry cells are very convenient to use for binding-posts and other similar purposes.Switches and Cut-OutsSwitches and cut-outs are used in electrical work for turning the current on and off.If the experimenter chooses to make them himself, care should be taken, to construct them in a strong and durable fashion, for they usually are subjected to considerable use, with consequent wear and tear.Fig. 94.—Binding-Post removed from the Carbon of a Dry Cell.Fig. 94.—Binding-Post removed from the Carbon of a Dry Cell.Several very simple home-made switches are illustrated in Figure 95.Fig. 95.—Simple Switches.Fig. 95.—Simple Switches.A, Single-Point Switch.B, Two-Point Switch.C, Three-Point Switch.D, Five-Point Switch.E, Lever with End Rolled up to form Handle.F, Lever with Handle made from part of a Spool.The first one shown (A) has one contact, formed by driving a brass-headed tack through a small strip of copper or brass.The movable arm is a strip of copper or brass, rolled up to form a handle at one end. The other end is pivoted with a brass screw. The brass screw passes through a small strip of copper or brass having a binding-post mounted on the end. A small copper washer should be placed between the movable arm and the copper strip to make the switch work more easily.A somewhat similar switch is shown byBin the same illustration, only in this case a handle made from half of a spool is used, instead of rolling up the end of the arm.The other illustrations show how the same method of construction may be applied to make switches having more than one "point" or contact.No dimensions have been given for constructing these switches, because it is doubtless easier for the young experimenter to use materials which he may have at hand, and construct a switch of his own proportions. Only one suggestion is necessary, and that is to bevel the under edges of the arm with a file, so that it will slip over the head of the brass tack more easily.The switches shown in Figure 96 are capable of carrying heavier currents than those just described, and more nearly approach the type used on lighting and power switchboards.The base may be made of wood, but preferably should be made of some insulating substance such as fiber or slate.Fig. 96.—Knife Switches.Fig. 96.—Knife Switches.The patterns for the metal parts are shown in Figure 97. These are cut from heavy sheet-brass or sheet-copper, and then bent into shape with a pair of flat-nosed pliers.The handle of the single-pole switch is driven on over the metal tongue.The double-pole switch is almost a duplicate of the single-pole type, but has two sets of levers and contacts, actuated by the handle, in place of one.Fig. 97.—Metal Parts for the Knife Switches.Fig. 97.—Metal Parts for the Knife Switches.The ends of the blades to which the handle is connected are turned over at right angles and a hard-wood cross-bar fastened between the ends. The handle is fastened to the center of the cross-bar.After the switch is assembled, bend the various parts until they "line up" that is, are in proper position in respect to each other, so that the blades will drop into the contacts without bringing pressure to bear on either one side or the other of the handle in order to force the blades into line.FusesFuses are used to prevent electrical instruments and wires from damage due to too much current flowing through. When an electric current passes through a resistance it producesheat.A fuse is usually a short piece of lead or some alloy which melts at a low temperature, and which is inserted in the circuit so that the current must flow through it. If too much current flows through the fuse it will become hot and melt, because of its low melting-point, thus interrupting the circuit and shutting the current off until the cause which occasioned the surplus current to flow can be ascertained.Fuses are rated according to the amount of current which is required to "blow" them out, and therefore are called 1, 3, 5, or 10 ampere fuses, as the case may be.Fig. 98.—Simple Fuses. *A*, Fuse-Block with plain Wire Fuse. *D*, Fuse-Block with Mica Fuse in position.Fig. 98.—Simple Fuses.A, Fuse-Block with plain Wire Fuse.D, Fuse-Block with Mica Fuse in position.When a fuse burns out in a trolley car or in a light or power circuit, it is because a greater amount of current is trying to pass than the circuit can safely carry. If a fuse were not placed in such a circuit so as to shut the current off before the danger point is reached, any electrical device might become "burned out," or in extreme cases, the wires become so hot as to cause a serious fire.Figure 98 shows several simple forms of fuses which the experimenter may easily make to protect the batteries, etc., from short circuits.The simplest possible fuse consists merely of a small piece of lead wire or a strip of thick tinfoil held between two binding-posts mounted upon a wooden block.The same form of fuse may be made from a strip of mica about two and one-half inches long and one-half an inch wide.A strip of thin sheet-copper is bent around the ends of the mica strip.A piece of fuse wire is stretched between the two copper contacts and fastened to each with a drop of solder. Fuse wire of any desired ampere-carrying capacity can be obtained from most electrical supply houses.Such a fuse is held in a mounting as shown byD. The contacts are made from sheet-copper or brass. They should spring together very tightly, so as to make perfect contact with the copper ends on the mica strip.Lightning-ArrestersLightning-arresters are used to protect all wires which run into a building from outdoors, especially telegraph or telephone wires, so that static electricity due to lightning will not damage the instruments.Lightning-arresters may be constructed in many ways and of different materials, but there are only two types for which the average experimenter will have any use.Fig. 99.—Lightning-Arrester and Ground-Wire Switch.Fig. 99.—Lightning-Arrester and Ground-Wire Switch.The arrester shown in Figure 99 is the type known as "lightning-arrester and ground-wire switch." It is used principally on telegraph lines.It consists of three pieces of sheet-brass about one-sixteenth of an inch thick, and shaped as shown byA,B, andCin Figure 100.The metal pieces are mounted on a wooden block with a narrow space of about one-thirty-second of an inch separating them.Fig. 100.—Home-made Lightning-Arrester.Fig. 100.—Home-made Lightning-Arrester.The two outside pieces are each fitted with two binding-posts, and the center triangular-shaped piece is fitted with one post.A hole about one-eighth of an inch in diameter is bored between each of the metal pieces.Make a tapered metal pin which can be placed tightly in the holes, and will make contact between the metal pieces.The two outside line wires of the telegraph circuit are connected to the outside metal piecesCandB.Ais connected to the earth or ground.In case of a lightning storm, if the wires become charged, the small space between the metal plates will permit the charge to jump across and pass harmlessly into the ground.If complete protection is desired, it is merely necessary to insert the plug in one of the holes, and thus "ground" either wire or short-circuit both of them.Fig. 101.—Lightning-Arrester for Telephone Wires.Fig. 101.—Lightning-Arrester for Telephone Wires.The lightning-arrester shown in Figure 101 is designed for service on telephone wires. It is an ordinary fuse provided with an arrester in the shape of two carbon blocks about one inch square. The blocks rest on a copper strip, and are held in place by a spring-strip connected toB.The carbon blocks are separated by a piece of thin sheet-mica, of the same size as the blocks.The post,B, is connected to one of the telephone-line wires near the point where it enters the building from outdoors. The post,A, is connected to the instrument;Cis connected to the ground.An arrester of this kind should be connected to each one of the telephone wires.If the line wires should happen to come into contact with a power wire, there is danger of damage to the instruments, but if an arrester is connected in the circuit such an occurrence would be prevented by the blowing out of the fuse. If the lines become charged by lightning, the charge can easily pass over the edge of the mica between the two blocks and into the ground.ELECTRICAL MEASURING INSTRUMENTS
CHAPTER VII ELECTRICAL APPURTENANCESWiresElectric currents are usually led from place to place, at will, by means of conductors calledwires. There are a great many kinds of wires, each adapted to some special purpose.Wires are usually covered with a material called aninsulator, in order to prevent the loss of electric current due to the wires coming into contact with other bodies or circuits. Insulators are substances which do not conduct electricity.Wires which areinsulatedby heavy braids of cotton fiber and then impregnated with some compound, such as creosote, are calledweather-proofwires, and are best adapted to outside service, where they must be exposed to the action of the elements.The wires used for interior wiring in buildings, etc., are usually insulated with rubber, over which is placed a cotton braid to protect the rubber.Rubber cannot well be used as an insulator for all wires, although its insulating value is very great, owing to the fact that it deteriorates under many conditions.Rubber-covered and weather-proof wires are made in a variety of insulations. Some may have only one insulating layer, while others have a great many. Different substances are used as insulators to adapt the wire to some special purpose. Copper is usually the only metal used to form the wire or conductor itself. The reason for this is that copper is a better conductor than any other metal except those known as precious metals, such as gold and silver, the cost of which prohibits their use for such purposes. The wire may be solid, or made up of a number of small conductors so that it is flexible.The various combinations of insulating layers, together with either a solid or a stranded conductor, have made possible a variety of current-carriers, known as:Theater or Stage CableElevator CableFixture WireTelephone WireMining CableFeeder CableBrewery CordHeater Cord, etc.depending upon the special use for which they were designed.NUMBER, DIAMETER, WEIGHT, LENGTH, AND RESISTANCE OF COPPER WIREThe wires which the young experimenter is likely to use in his work the most are known asmagnet wires, and are used for making electro-magnets, coils, and various windings. Magnet wires may be insulated with either silk, cotton, or enamel.NUMBER, DIAMETER, WEIGHT, LENGTH, AND RESISTANCE OF COPPER WIRESilk-covered and cotton-covered wires may be obtained with either a single or double covering.Wires with a single covering of silk or enamel are used when it is desirable to save space, for the covering of these two classes of magnet wires is thinner than either the cotton or double-silk-covered wire, and consequently they require less room for winding.The size of the wire is indicated by its diameter, and in the United States is measured by the Brown and Sharpe gauge, often indicated by the term, "B. & S."The preceding table shows the various sizes of wire of the Brown and Sharpe gauge, and also several of their characteristics, such as weight, resistance, etc.InsulatorsThe covering placed over wires is not the only precaution taken to insulate them, but in the case of permanent wiring they are usually mounted on glass or porcelain supports.Fig. 89.—Staples and Wooden Cleat used for running Low Voltage Wires.Fig. 89.—Staples and Wooden Cleat used for running Low Voltage Wires.Wires used for batteries, bells, telephones, etc., operated by batteries and where the voltage is not over 20 volts, may be run underinsulatedstaples or wooden cleats inside of a building. If outside and exposed to the weather, they should be mounted on suitable glass or porcelain knobs.Fig. 90.—Porcelain Insulators to support Electric Light Wires.Fig. 90.—Porcelain Insulators to support Electric Light Wires.Electric-light wires for inside use are commonly supported by insulators made of porcelain and known as cleats, knobs, and tubes according to the shape.Telegraph, telephone, and power lines are usually supported by glass knobs or large porcelain insulators which screw on to wooden pins.Fig. 91.—Glass Insulator Binding-Posts and Pin used to support Telegraph and Telephone wires.Fig. 91.—Glass Insulator Binding-Posts and Pin used to support Telegraph and Telephone wires.Binding-PostsBinding-posts are the most convenient device to make quick connections between wires and other parts of electrical apparatus.Binding-posts may be either made or purchased. Those which are purchased are of course the best, and will add greatly to the appearance of any instrument upon which they are mounted.Several of the best-known types of manufactured posts are shown in Figure 92.Fig. 92.—Types of Binding-Posts.Fig. 92.—Types of Binding-Posts.Figure 93 shows different ways of making simple binding-posts and connectors from screws, washers, screw-eyes, and strips of metal. The drawings are self-explanatory and should need no comment.Fig. 93.—Home-made Binding-Posts.Fig. 93.—Home-made Binding-Posts.The screws and nuts obtainable from old dry cells are very convenient to use for binding-posts and other similar purposes.Switches and Cut-OutsSwitches and cut-outs are used in electrical work for turning the current on and off.If the experimenter chooses to make them himself, care should be taken, to construct them in a strong and durable fashion, for they usually are subjected to considerable use, with consequent wear and tear.Fig. 94.—Binding-Post removed from the Carbon of a Dry Cell.Fig. 94.—Binding-Post removed from the Carbon of a Dry Cell.Several very simple home-made switches are illustrated in Figure 95.Fig. 95.—Simple Switches.Fig. 95.—Simple Switches.A, Single-Point Switch.B, Two-Point Switch.C, Three-Point Switch.D, Five-Point Switch.E, Lever with End Rolled up to form Handle.F, Lever with Handle made from part of a Spool.The first one shown (A) has one contact, formed by driving a brass-headed tack through a small strip of copper or brass.The movable arm is a strip of copper or brass, rolled up to form a handle at one end. The other end is pivoted with a brass screw. The brass screw passes through a small strip of copper or brass having a binding-post mounted on the end. A small copper washer should be placed between the movable arm and the copper strip to make the switch work more easily.A somewhat similar switch is shown byBin the same illustration, only in this case a handle made from half of a spool is used, instead of rolling up the end of the arm.The other illustrations show how the same method of construction may be applied to make switches having more than one "point" or contact.No dimensions have been given for constructing these switches, because it is doubtless easier for the young experimenter to use materials which he may have at hand, and construct a switch of his own proportions. Only one suggestion is necessary, and that is to bevel the under edges of the arm with a file, so that it will slip over the head of the brass tack more easily.The switches shown in Figure 96 are capable of carrying heavier currents than those just described, and more nearly approach the type used on lighting and power switchboards.The base may be made of wood, but preferably should be made of some insulating substance such as fiber or slate.Fig. 96.—Knife Switches.Fig. 96.—Knife Switches.The patterns for the metal parts are shown in Figure 97. These are cut from heavy sheet-brass or sheet-copper, and then bent into shape with a pair of flat-nosed pliers.The handle of the single-pole switch is driven on over the metal tongue.The double-pole switch is almost a duplicate of the single-pole type, but has two sets of levers and contacts, actuated by the handle, in place of one.Fig. 97.—Metal Parts for the Knife Switches.Fig. 97.—Metal Parts for the Knife Switches.The ends of the blades to which the handle is connected are turned over at right angles and a hard-wood cross-bar fastened between the ends. The handle is fastened to the center of the cross-bar.After the switch is assembled, bend the various parts until they "line up" that is, are in proper position in respect to each other, so that the blades will drop into the contacts without bringing pressure to bear on either one side or the other of the handle in order to force the blades into line.FusesFuses are used to prevent electrical instruments and wires from damage due to too much current flowing through. When an electric current passes through a resistance it producesheat.A fuse is usually a short piece of lead or some alloy which melts at a low temperature, and which is inserted in the circuit so that the current must flow through it. If too much current flows through the fuse it will become hot and melt, because of its low melting-point, thus interrupting the circuit and shutting the current off until the cause which occasioned the surplus current to flow can be ascertained.Fuses are rated according to the amount of current which is required to "blow" them out, and therefore are called 1, 3, 5, or 10 ampere fuses, as the case may be.Fig. 98.—Simple Fuses. *A*, Fuse-Block with plain Wire Fuse. *D*, Fuse-Block with Mica Fuse in position.Fig. 98.—Simple Fuses.A, Fuse-Block with plain Wire Fuse.D, Fuse-Block with Mica Fuse in position.When a fuse burns out in a trolley car or in a light or power circuit, it is because a greater amount of current is trying to pass than the circuit can safely carry. If a fuse were not placed in such a circuit so as to shut the current off before the danger point is reached, any electrical device might become "burned out," or in extreme cases, the wires become so hot as to cause a serious fire.Figure 98 shows several simple forms of fuses which the experimenter may easily make to protect the batteries, etc., from short circuits.The simplest possible fuse consists merely of a small piece of lead wire or a strip of thick tinfoil held between two binding-posts mounted upon a wooden block.The same form of fuse may be made from a strip of mica about two and one-half inches long and one-half an inch wide.A strip of thin sheet-copper is bent around the ends of the mica strip.A piece of fuse wire is stretched between the two copper contacts and fastened to each with a drop of solder. Fuse wire of any desired ampere-carrying capacity can be obtained from most electrical supply houses.Such a fuse is held in a mounting as shown byD. The contacts are made from sheet-copper or brass. They should spring together very tightly, so as to make perfect contact with the copper ends on the mica strip.Lightning-ArrestersLightning-arresters are used to protect all wires which run into a building from outdoors, especially telegraph or telephone wires, so that static electricity due to lightning will not damage the instruments.Lightning-arresters may be constructed in many ways and of different materials, but there are only two types for which the average experimenter will have any use.Fig. 99.—Lightning-Arrester and Ground-Wire Switch.Fig. 99.—Lightning-Arrester and Ground-Wire Switch.The arrester shown in Figure 99 is the type known as "lightning-arrester and ground-wire switch." It is used principally on telegraph lines.It consists of three pieces of sheet-brass about one-sixteenth of an inch thick, and shaped as shown byA,B, andCin Figure 100.The metal pieces are mounted on a wooden block with a narrow space of about one-thirty-second of an inch separating them.Fig. 100.—Home-made Lightning-Arrester.Fig. 100.—Home-made Lightning-Arrester.The two outside pieces are each fitted with two binding-posts, and the center triangular-shaped piece is fitted with one post.A hole about one-eighth of an inch in diameter is bored between each of the metal pieces.Make a tapered metal pin which can be placed tightly in the holes, and will make contact between the metal pieces.The two outside line wires of the telegraph circuit are connected to the outside metal piecesCandB.Ais connected to the earth or ground.In case of a lightning storm, if the wires become charged, the small space between the metal plates will permit the charge to jump across and pass harmlessly into the ground.If complete protection is desired, it is merely necessary to insert the plug in one of the holes, and thus "ground" either wire or short-circuit both of them.Fig. 101.—Lightning-Arrester for Telephone Wires.Fig. 101.—Lightning-Arrester for Telephone Wires.The lightning-arrester shown in Figure 101 is designed for service on telephone wires. It is an ordinary fuse provided with an arrester in the shape of two carbon blocks about one inch square. The blocks rest on a copper strip, and are held in place by a spring-strip connected toB.The carbon blocks are separated by a piece of thin sheet-mica, of the same size as the blocks.The post,B, is connected to one of the telephone-line wires near the point where it enters the building from outdoors. The post,A, is connected to the instrument;Cis connected to the ground.An arrester of this kind should be connected to each one of the telephone wires.If the line wires should happen to come into contact with a power wire, there is danger of damage to the instruments, but if an arrester is connected in the circuit such an occurrence would be prevented by the blowing out of the fuse. If the lines become charged by lightning, the charge can easily pass over the edge of the mica between the two blocks and into the ground.ELECTRICAL MEASURING INSTRUMENTS
CHAPTER VII ELECTRICAL APPURTENANCESWiresElectric currents are usually led from place to place, at will, by means of conductors calledwires. There are a great many kinds of wires, each adapted to some special purpose.Wires are usually covered with a material called aninsulator, in order to prevent the loss of electric current due to the wires coming into contact with other bodies or circuits. Insulators are substances which do not conduct electricity.Wires which areinsulatedby heavy braids of cotton fiber and then impregnated with some compound, such as creosote, are calledweather-proofwires, and are best adapted to outside service, where they must be exposed to the action of the elements.The wires used for interior wiring in buildings, etc., are usually insulated with rubber, over which is placed a cotton braid to protect the rubber.Rubber cannot well be used as an insulator for all wires, although its insulating value is very great, owing to the fact that it deteriorates under many conditions.Rubber-covered and weather-proof wires are made in a variety of insulations. Some may have only one insulating layer, while others have a great many. Different substances are used as insulators to adapt the wire to some special purpose. Copper is usually the only metal used to form the wire or conductor itself. The reason for this is that copper is a better conductor than any other metal except those known as precious metals, such as gold and silver, the cost of which prohibits their use for such purposes. The wire may be solid, or made up of a number of small conductors so that it is flexible.The various combinations of insulating layers, together with either a solid or a stranded conductor, have made possible a variety of current-carriers, known as:Theater or Stage CableElevator CableFixture WireTelephone WireMining CableFeeder CableBrewery CordHeater Cord, etc.depending upon the special use for which they were designed.NUMBER, DIAMETER, WEIGHT, LENGTH, AND RESISTANCE OF COPPER WIREThe wires which the young experimenter is likely to use in his work the most are known asmagnet wires, and are used for making electro-magnets, coils, and various windings. Magnet wires may be insulated with either silk, cotton, or enamel.NUMBER, DIAMETER, WEIGHT, LENGTH, AND RESISTANCE OF COPPER WIRESilk-covered and cotton-covered wires may be obtained with either a single or double covering.Wires with a single covering of silk or enamel are used when it is desirable to save space, for the covering of these two classes of magnet wires is thinner than either the cotton or double-silk-covered wire, and consequently they require less room for winding.The size of the wire is indicated by its diameter, and in the United States is measured by the Brown and Sharpe gauge, often indicated by the term, "B. & S."The preceding table shows the various sizes of wire of the Brown and Sharpe gauge, and also several of their characteristics, such as weight, resistance, etc.InsulatorsThe covering placed over wires is not the only precaution taken to insulate them, but in the case of permanent wiring they are usually mounted on glass or porcelain supports.Fig. 89.—Staples and Wooden Cleat used for running Low Voltage Wires.Fig. 89.—Staples and Wooden Cleat used for running Low Voltage Wires.Wires used for batteries, bells, telephones, etc., operated by batteries and where the voltage is not over 20 volts, may be run underinsulatedstaples or wooden cleats inside of a building. If outside and exposed to the weather, they should be mounted on suitable glass or porcelain knobs.Fig. 90.—Porcelain Insulators to support Electric Light Wires.Fig. 90.—Porcelain Insulators to support Electric Light Wires.Electric-light wires for inside use are commonly supported by insulators made of porcelain and known as cleats, knobs, and tubes according to the shape.Telegraph, telephone, and power lines are usually supported by glass knobs or large porcelain insulators which screw on to wooden pins.Fig. 91.—Glass Insulator Binding-Posts and Pin used to support Telegraph and Telephone wires.Fig. 91.—Glass Insulator Binding-Posts and Pin used to support Telegraph and Telephone wires.Binding-PostsBinding-posts are the most convenient device to make quick connections between wires and other parts of electrical apparatus.Binding-posts may be either made or purchased. Those which are purchased are of course the best, and will add greatly to the appearance of any instrument upon which they are mounted.Several of the best-known types of manufactured posts are shown in Figure 92.Fig. 92.—Types of Binding-Posts.Fig. 92.—Types of Binding-Posts.Figure 93 shows different ways of making simple binding-posts and connectors from screws, washers, screw-eyes, and strips of metal. The drawings are self-explanatory and should need no comment.Fig. 93.—Home-made Binding-Posts.Fig. 93.—Home-made Binding-Posts.The screws and nuts obtainable from old dry cells are very convenient to use for binding-posts and other similar purposes.Switches and Cut-OutsSwitches and cut-outs are used in electrical work for turning the current on and off.If the experimenter chooses to make them himself, care should be taken, to construct them in a strong and durable fashion, for they usually are subjected to considerable use, with consequent wear and tear.Fig. 94.—Binding-Post removed from the Carbon of a Dry Cell.Fig. 94.—Binding-Post removed from the Carbon of a Dry Cell.Several very simple home-made switches are illustrated in Figure 95.Fig. 95.—Simple Switches.Fig. 95.—Simple Switches.A, Single-Point Switch.B, Two-Point Switch.C, Three-Point Switch.D, Five-Point Switch.E, Lever with End Rolled up to form Handle.F, Lever with Handle made from part of a Spool.The first one shown (A) has one contact, formed by driving a brass-headed tack through a small strip of copper or brass.The movable arm is a strip of copper or brass, rolled up to form a handle at one end. The other end is pivoted with a brass screw. The brass screw passes through a small strip of copper or brass having a binding-post mounted on the end. A small copper washer should be placed between the movable arm and the copper strip to make the switch work more easily.A somewhat similar switch is shown byBin the same illustration, only in this case a handle made from half of a spool is used, instead of rolling up the end of the arm.The other illustrations show how the same method of construction may be applied to make switches having more than one "point" or contact.No dimensions have been given for constructing these switches, because it is doubtless easier for the young experimenter to use materials which he may have at hand, and construct a switch of his own proportions. Only one suggestion is necessary, and that is to bevel the under edges of the arm with a file, so that it will slip over the head of the brass tack more easily.The switches shown in Figure 96 are capable of carrying heavier currents than those just described, and more nearly approach the type used on lighting and power switchboards.The base may be made of wood, but preferably should be made of some insulating substance such as fiber or slate.Fig. 96.—Knife Switches.Fig. 96.—Knife Switches.The patterns for the metal parts are shown in Figure 97. These are cut from heavy sheet-brass or sheet-copper, and then bent into shape with a pair of flat-nosed pliers.The handle of the single-pole switch is driven on over the metal tongue.The double-pole switch is almost a duplicate of the single-pole type, but has two sets of levers and contacts, actuated by the handle, in place of one.Fig. 97.—Metal Parts for the Knife Switches.Fig. 97.—Metal Parts for the Knife Switches.The ends of the blades to which the handle is connected are turned over at right angles and a hard-wood cross-bar fastened between the ends. The handle is fastened to the center of the cross-bar.After the switch is assembled, bend the various parts until they "line up" that is, are in proper position in respect to each other, so that the blades will drop into the contacts without bringing pressure to bear on either one side or the other of the handle in order to force the blades into line.FusesFuses are used to prevent electrical instruments and wires from damage due to too much current flowing through. When an electric current passes through a resistance it producesheat.A fuse is usually a short piece of lead or some alloy which melts at a low temperature, and which is inserted in the circuit so that the current must flow through it. If too much current flows through the fuse it will become hot and melt, because of its low melting-point, thus interrupting the circuit and shutting the current off until the cause which occasioned the surplus current to flow can be ascertained.Fuses are rated according to the amount of current which is required to "blow" them out, and therefore are called 1, 3, 5, or 10 ampere fuses, as the case may be.Fig. 98.—Simple Fuses. *A*, Fuse-Block with plain Wire Fuse. *D*, Fuse-Block with Mica Fuse in position.Fig. 98.—Simple Fuses.A, Fuse-Block with plain Wire Fuse.D, Fuse-Block with Mica Fuse in position.When a fuse burns out in a trolley car or in a light or power circuit, it is because a greater amount of current is trying to pass than the circuit can safely carry. If a fuse were not placed in such a circuit so as to shut the current off before the danger point is reached, any electrical device might become "burned out," or in extreme cases, the wires become so hot as to cause a serious fire.Figure 98 shows several simple forms of fuses which the experimenter may easily make to protect the batteries, etc., from short circuits.The simplest possible fuse consists merely of a small piece of lead wire or a strip of thick tinfoil held between two binding-posts mounted upon a wooden block.The same form of fuse may be made from a strip of mica about two and one-half inches long and one-half an inch wide.A strip of thin sheet-copper is bent around the ends of the mica strip.A piece of fuse wire is stretched between the two copper contacts and fastened to each with a drop of solder. Fuse wire of any desired ampere-carrying capacity can be obtained from most electrical supply houses.Such a fuse is held in a mounting as shown byD. The contacts are made from sheet-copper or brass. They should spring together very tightly, so as to make perfect contact with the copper ends on the mica strip.Lightning-ArrestersLightning-arresters are used to protect all wires which run into a building from outdoors, especially telegraph or telephone wires, so that static electricity due to lightning will not damage the instruments.Lightning-arresters may be constructed in many ways and of different materials, but there are only two types for which the average experimenter will have any use.Fig. 99.—Lightning-Arrester and Ground-Wire Switch.Fig. 99.—Lightning-Arrester and Ground-Wire Switch.The arrester shown in Figure 99 is the type known as "lightning-arrester and ground-wire switch." It is used principally on telegraph lines.It consists of three pieces of sheet-brass about one-sixteenth of an inch thick, and shaped as shown byA,B, andCin Figure 100.The metal pieces are mounted on a wooden block with a narrow space of about one-thirty-second of an inch separating them.Fig. 100.—Home-made Lightning-Arrester.Fig. 100.—Home-made Lightning-Arrester.The two outside pieces are each fitted with two binding-posts, and the center triangular-shaped piece is fitted with one post.A hole about one-eighth of an inch in diameter is bored between each of the metal pieces.Make a tapered metal pin which can be placed tightly in the holes, and will make contact between the metal pieces.The two outside line wires of the telegraph circuit are connected to the outside metal piecesCandB.Ais connected to the earth or ground.In case of a lightning storm, if the wires become charged, the small space between the metal plates will permit the charge to jump across and pass harmlessly into the ground.If complete protection is desired, it is merely necessary to insert the plug in one of the holes, and thus "ground" either wire or short-circuit both of them.Fig. 101.—Lightning-Arrester for Telephone Wires.Fig. 101.—Lightning-Arrester for Telephone Wires.The lightning-arrester shown in Figure 101 is designed for service on telephone wires. It is an ordinary fuse provided with an arrester in the shape of two carbon blocks about one inch square. The blocks rest on a copper strip, and are held in place by a spring-strip connected toB.The carbon blocks are separated by a piece of thin sheet-mica, of the same size as the blocks.The post,B, is connected to one of the telephone-line wires near the point where it enters the building from outdoors. The post,A, is connected to the instrument;Cis connected to the ground.An arrester of this kind should be connected to each one of the telephone wires.If the line wires should happen to come into contact with a power wire, there is danger of damage to the instruments, but if an arrester is connected in the circuit such an occurrence would be prevented by the blowing out of the fuse. If the lines become charged by lightning, the charge can easily pass over the edge of the mica between the two blocks and into the ground.ELECTRICAL MEASURING INSTRUMENTS
WiresElectric currents are usually led from place to place, at will, by means of conductors calledwires. There are a great many kinds of wires, each adapted to some special purpose.Wires are usually covered with a material called aninsulator, in order to prevent the loss of electric current due to the wires coming into contact with other bodies or circuits. Insulators are substances which do not conduct electricity.Wires which areinsulatedby heavy braids of cotton fiber and then impregnated with some compound, such as creosote, are calledweather-proofwires, and are best adapted to outside service, where they must be exposed to the action of the elements.The wires used for interior wiring in buildings, etc., are usually insulated with rubber, over which is placed a cotton braid to protect the rubber.Rubber cannot well be used as an insulator for all wires, although its insulating value is very great, owing to the fact that it deteriorates under many conditions.Rubber-covered and weather-proof wires are made in a variety of insulations. Some may have only one insulating layer, while others have a great many. Different substances are used as insulators to adapt the wire to some special purpose. Copper is usually the only metal used to form the wire or conductor itself. The reason for this is that copper is a better conductor than any other metal except those known as precious metals, such as gold and silver, the cost of which prohibits their use for such purposes. The wire may be solid, or made up of a number of small conductors so that it is flexible.The various combinations of insulating layers, together with either a solid or a stranded conductor, have made possible a variety of current-carriers, known as:Theater or Stage CableElevator CableFixture WireTelephone WireMining CableFeeder CableBrewery CordHeater Cord, etc.depending upon the special use for which they were designed.NUMBER, DIAMETER, WEIGHT, LENGTH, AND RESISTANCE OF COPPER WIREThe wires which the young experimenter is likely to use in his work the most are known asmagnet wires, and are used for making electro-magnets, coils, and various windings. Magnet wires may be insulated with either silk, cotton, or enamel.NUMBER, DIAMETER, WEIGHT, LENGTH, AND RESISTANCE OF COPPER WIRESilk-covered and cotton-covered wires may be obtained with either a single or double covering.Wires with a single covering of silk or enamel are used when it is desirable to save space, for the covering of these two classes of magnet wires is thinner than either the cotton or double-silk-covered wire, and consequently they require less room for winding.The size of the wire is indicated by its diameter, and in the United States is measured by the Brown and Sharpe gauge, often indicated by the term, "B. & S."The preceding table shows the various sizes of wire of the Brown and Sharpe gauge, and also several of their characteristics, such as weight, resistance, etc.
Electric currents are usually led from place to place, at will, by means of conductors calledwires. There are a great many kinds of wires, each adapted to some special purpose.
Wires are usually covered with a material called aninsulator, in order to prevent the loss of electric current due to the wires coming into contact with other bodies or circuits. Insulators are substances which do not conduct electricity.
Wires which areinsulatedby heavy braids of cotton fiber and then impregnated with some compound, such as creosote, are calledweather-proofwires, and are best adapted to outside service, where they must be exposed to the action of the elements.
The wires used for interior wiring in buildings, etc., are usually insulated with rubber, over which is placed a cotton braid to protect the rubber.
Rubber cannot well be used as an insulator for all wires, although its insulating value is very great, owing to the fact that it deteriorates under many conditions.
Rubber-covered and weather-proof wires are made in a variety of insulations. Some may have only one insulating layer, while others have a great many. Different substances are used as insulators to adapt the wire to some special purpose. Copper is usually the only metal used to form the wire or conductor itself. The reason for this is that copper is a better conductor than any other metal except those known as precious metals, such as gold and silver, the cost of which prohibits their use for such purposes. The wire may be solid, or made up of a number of small conductors so that it is flexible.
The various combinations of insulating layers, together with either a solid or a stranded conductor, have made possible a variety of current-carriers, known as:
Theater or Stage CableElevator CableFixture WireTelephone WireMining CableFeeder CableBrewery CordHeater Cord, etc.
Theater or Stage Cable
Elevator Cable
Fixture Wire
Telephone Wire
Mining Cable
Feeder Cable
Brewery Cord
Heater Cord, etc.
depending upon the special use for which they were designed.
NUMBER, DIAMETER, WEIGHT, LENGTH, AND RESISTANCE OF COPPER WIRE
The wires which the young experimenter is likely to use in his work the most are known asmagnet wires, and are used for making electro-magnets, coils, and various windings. Magnet wires may be insulated with either silk, cotton, or enamel.
NUMBER, DIAMETER, WEIGHT, LENGTH, AND RESISTANCE OF COPPER WIRE
Silk-covered and cotton-covered wires may be obtained with either a single or double covering.
Wires with a single covering of silk or enamel are used when it is desirable to save space, for the covering of these two classes of magnet wires is thinner than either the cotton or double-silk-covered wire, and consequently they require less room for winding.
The size of the wire is indicated by its diameter, and in the United States is measured by the Brown and Sharpe gauge, often indicated by the term, "B. & S."
The preceding table shows the various sizes of wire of the Brown and Sharpe gauge, and also several of their characteristics, such as weight, resistance, etc.
InsulatorsThe covering placed over wires is not the only precaution taken to insulate them, but in the case of permanent wiring they are usually mounted on glass or porcelain supports.Fig. 89.—Staples and Wooden Cleat used for running Low Voltage Wires.Fig. 89.—Staples and Wooden Cleat used for running Low Voltage Wires.Wires used for batteries, bells, telephones, etc., operated by batteries and where the voltage is not over 20 volts, may be run underinsulatedstaples or wooden cleats inside of a building. If outside and exposed to the weather, they should be mounted on suitable glass or porcelain knobs.Fig. 90.—Porcelain Insulators to support Electric Light Wires.Fig. 90.—Porcelain Insulators to support Electric Light Wires.Electric-light wires for inside use are commonly supported by insulators made of porcelain and known as cleats, knobs, and tubes according to the shape.Telegraph, telephone, and power lines are usually supported by glass knobs or large porcelain insulators which screw on to wooden pins.Fig. 91.—Glass Insulator Binding-Posts and Pin used to support Telegraph and Telephone wires.Fig. 91.—Glass Insulator Binding-Posts and Pin used to support Telegraph and Telephone wires.
The covering placed over wires is not the only precaution taken to insulate them, but in the case of permanent wiring they are usually mounted on glass or porcelain supports.
Fig. 89.—Staples and Wooden Cleat used for running Low Voltage Wires.Fig. 89.—Staples and Wooden Cleat used for running Low Voltage Wires.
Fig. 89.—Staples and Wooden Cleat used for running Low Voltage Wires.
Wires used for batteries, bells, telephones, etc., operated by batteries and where the voltage is not over 20 volts, may be run underinsulatedstaples or wooden cleats inside of a building. If outside and exposed to the weather, they should be mounted on suitable glass or porcelain knobs.
Fig. 90.—Porcelain Insulators to support Electric Light Wires.Fig. 90.—Porcelain Insulators to support Electric Light Wires.
Fig. 90.—Porcelain Insulators to support Electric Light Wires.
Electric-light wires for inside use are commonly supported by insulators made of porcelain and known as cleats, knobs, and tubes according to the shape.
Telegraph, telephone, and power lines are usually supported by glass knobs or large porcelain insulators which screw on to wooden pins.
Fig. 91.—Glass Insulator Binding-Posts and Pin used to support Telegraph and Telephone wires.Fig. 91.—Glass Insulator Binding-Posts and Pin used to support Telegraph and Telephone wires.
Fig. 91.—Glass Insulator Binding-Posts and Pin used to support Telegraph and Telephone wires.
Binding-PostsBinding-posts are the most convenient device to make quick connections between wires and other parts of electrical apparatus.Binding-posts may be either made or purchased. Those which are purchased are of course the best, and will add greatly to the appearance of any instrument upon which they are mounted.Several of the best-known types of manufactured posts are shown in Figure 92.Fig. 92.—Types of Binding-Posts.Fig. 92.—Types of Binding-Posts.Figure 93 shows different ways of making simple binding-posts and connectors from screws, washers, screw-eyes, and strips of metal. The drawings are self-explanatory and should need no comment.Fig. 93.—Home-made Binding-Posts.Fig. 93.—Home-made Binding-Posts.The screws and nuts obtainable from old dry cells are very convenient to use for binding-posts and other similar purposes.
Binding-posts are the most convenient device to make quick connections between wires and other parts of electrical apparatus.
Binding-posts may be either made or purchased. Those which are purchased are of course the best, and will add greatly to the appearance of any instrument upon which they are mounted.
Several of the best-known types of manufactured posts are shown in Figure 92.
Fig. 92.—Types of Binding-Posts.Fig. 92.—Types of Binding-Posts.
Fig. 92.—Types of Binding-Posts.
Figure 93 shows different ways of making simple binding-posts and connectors from screws, washers, screw-eyes, and strips of metal. The drawings are self-explanatory and should need no comment.
Fig. 93.—Home-made Binding-Posts.Fig. 93.—Home-made Binding-Posts.
Fig. 93.—Home-made Binding-Posts.
The screws and nuts obtainable from old dry cells are very convenient to use for binding-posts and other similar purposes.
Switches and Cut-OutsSwitches and cut-outs are used in electrical work for turning the current on and off.If the experimenter chooses to make them himself, care should be taken, to construct them in a strong and durable fashion, for they usually are subjected to considerable use, with consequent wear and tear.Fig. 94.—Binding-Post removed from the Carbon of a Dry Cell.Fig. 94.—Binding-Post removed from the Carbon of a Dry Cell.Several very simple home-made switches are illustrated in Figure 95.Fig. 95.—Simple Switches.Fig. 95.—Simple Switches.A, Single-Point Switch.B, Two-Point Switch.C, Three-Point Switch.D, Five-Point Switch.E, Lever with End Rolled up to form Handle.F, Lever with Handle made from part of a Spool.The first one shown (A) has one contact, formed by driving a brass-headed tack through a small strip of copper or brass.The movable arm is a strip of copper or brass, rolled up to form a handle at one end. The other end is pivoted with a brass screw. The brass screw passes through a small strip of copper or brass having a binding-post mounted on the end. A small copper washer should be placed between the movable arm and the copper strip to make the switch work more easily.A somewhat similar switch is shown byBin the same illustration, only in this case a handle made from half of a spool is used, instead of rolling up the end of the arm.The other illustrations show how the same method of construction may be applied to make switches having more than one "point" or contact.No dimensions have been given for constructing these switches, because it is doubtless easier for the young experimenter to use materials which he may have at hand, and construct a switch of his own proportions. Only one suggestion is necessary, and that is to bevel the under edges of the arm with a file, so that it will slip over the head of the brass tack more easily.The switches shown in Figure 96 are capable of carrying heavier currents than those just described, and more nearly approach the type used on lighting and power switchboards.The base may be made of wood, but preferably should be made of some insulating substance such as fiber or slate.Fig. 96.—Knife Switches.Fig. 96.—Knife Switches.The patterns for the metal parts are shown in Figure 97. These are cut from heavy sheet-brass or sheet-copper, and then bent into shape with a pair of flat-nosed pliers.The handle of the single-pole switch is driven on over the metal tongue.The double-pole switch is almost a duplicate of the single-pole type, but has two sets of levers and contacts, actuated by the handle, in place of one.Fig. 97.—Metal Parts for the Knife Switches.Fig. 97.—Metal Parts for the Knife Switches.The ends of the blades to which the handle is connected are turned over at right angles and a hard-wood cross-bar fastened between the ends. The handle is fastened to the center of the cross-bar.After the switch is assembled, bend the various parts until they "line up" that is, are in proper position in respect to each other, so that the blades will drop into the contacts without bringing pressure to bear on either one side or the other of the handle in order to force the blades into line.
Switches and cut-outs are used in electrical work for turning the current on and off.
If the experimenter chooses to make them himself, care should be taken, to construct them in a strong and durable fashion, for they usually are subjected to considerable use, with consequent wear and tear.
Fig. 94.—Binding-Post removed from the Carbon of a Dry Cell.Fig. 94.—Binding-Post removed from the Carbon of a Dry Cell.
Fig. 94.—Binding-Post removed from the Carbon of a Dry Cell.
Several very simple home-made switches are illustrated in Figure 95.
Fig. 95.—Simple Switches.Fig. 95.—Simple Switches.A, Single-Point Switch.B, Two-Point Switch.C, Three-Point Switch.D, Five-Point Switch.E, Lever with End Rolled up to form Handle.F, Lever with Handle made from part of a Spool.
Fig. 95.—Simple Switches.A, Single-Point Switch.B, Two-Point Switch.C, Three-Point Switch.D, Five-Point Switch.E, Lever with End Rolled up to form Handle.F, Lever with Handle made from part of a Spool.
The first one shown (A) has one contact, formed by driving a brass-headed tack through a small strip of copper or brass.
The movable arm is a strip of copper or brass, rolled up to form a handle at one end. The other end is pivoted with a brass screw. The brass screw passes through a small strip of copper or brass having a binding-post mounted on the end. A small copper washer should be placed between the movable arm and the copper strip to make the switch work more easily.
A somewhat similar switch is shown byBin the same illustration, only in this case a handle made from half of a spool is used, instead of rolling up the end of the arm.
The other illustrations show how the same method of construction may be applied to make switches having more than one "point" or contact.
No dimensions have been given for constructing these switches, because it is doubtless easier for the young experimenter to use materials which he may have at hand, and construct a switch of his own proportions. Only one suggestion is necessary, and that is to bevel the under edges of the arm with a file, so that it will slip over the head of the brass tack more easily.
The switches shown in Figure 96 are capable of carrying heavier currents than those just described, and more nearly approach the type used on lighting and power switchboards.
The base may be made of wood, but preferably should be made of some insulating substance such as fiber or slate.
Fig. 96.—Knife Switches.Fig. 96.—Knife Switches.
Fig. 96.—Knife Switches.
The patterns for the metal parts are shown in Figure 97. These are cut from heavy sheet-brass or sheet-copper, and then bent into shape with a pair of flat-nosed pliers.
The handle of the single-pole switch is driven on over the metal tongue.
The double-pole switch is almost a duplicate of the single-pole type, but has two sets of levers and contacts, actuated by the handle, in place of one.
Fig. 97.—Metal Parts for the Knife Switches.Fig. 97.—Metal Parts for the Knife Switches.
Fig. 97.—Metal Parts for the Knife Switches.
The ends of the blades to which the handle is connected are turned over at right angles and a hard-wood cross-bar fastened between the ends. The handle is fastened to the center of the cross-bar.
After the switch is assembled, bend the various parts until they "line up" that is, are in proper position in respect to each other, so that the blades will drop into the contacts without bringing pressure to bear on either one side or the other of the handle in order to force the blades into line.
FusesFuses are used to prevent electrical instruments and wires from damage due to too much current flowing through. When an electric current passes through a resistance it producesheat.A fuse is usually a short piece of lead or some alloy which melts at a low temperature, and which is inserted in the circuit so that the current must flow through it. If too much current flows through the fuse it will become hot and melt, because of its low melting-point, thus interrupting the circuit and shutting the current off until the cause which occasioned the surplus current to flow can be ascertained.Fuses are rated according to the amount of current which is required to "blow" them out, and therefore are called 1, 3, 5, or 10 ampere fuses, as the case may be.Fig. 98.—Simple Fuses. *A*, Fuse-Block with plain Wire Fuse. *D*, Fuse-Block with Mica Fuse in position.Fig. 98.—Simple Fuses.A, Fuse-Block with plain Wire Fuse.D, Fuse-Block with Mica Fuse in position.When a fuse burns out in a trolley car or in a light or power circuit, it is because a greater amount of current is trying to pass than the circuit can safely carry. If a fuse were not placed in such a circuit so as to shut the current off before the danger point is reached, any electrical device might become "burned out," or in extreme cases, the wires become so hot as to cause a serious fire.Figure 98 shows several simple forms of fuses which the experimenter may easily make to protect the batteries, etc., from short circuits.The simplest possible fuse consists merely of a small piece of lead wire or a strip of thick tinfoil held between two binding-posts mounted upon a wooden block.The same form of fuse may be made from a strip of mica about two and one-half inches long and one-half an inch wide.A strip of thin sheet-copper is bent around the ends of the mica strip.A piece of fuse wire is stretched between the two copper contacts and fastened to each with a drop of solder. Fuse wire of any desired ampere-carrying capacity can be obtained from most electrical supply houses.Such a fuse is held in a mounting as shown byD. The contacts are made from sheet-copper or brass. They should spring together very tightly, so as to make perfect contact with the copper ends on the mica strip.
Fuses are used to prevent electrical instruments and wires from damage due to too much current flowing through. When an electric current passes through a resistance it producesheat.
A fuse is usually a short piece of lead or some alloy which melts at a low temperature, and which is inserted in the circuit so that the current must flow through it. If too much current flows through the fuse it will become hot and melt, because of its low melting-point, thus interrupting the circuit and shutting the current off until the cause which occasioned the surplus current to flow can be ascertained.
Fuses are rated according to the amount of current which is required to "blow" them out, and therefore are called 1, 3, 5, or 10 ampere fuses, as the case may be.
Fig. 98.—Simple Fuses. *A*, Fuse-Block with plain Wire Fuse. *D*, Fuse-Block with Mica Fuse in position.Fig. 98.—Simple Fuses.A, Fuse-Block with plain Wire Fuse.D, Fuse-Block with Mica Fuse in position.
Fig. 98.—Simple Fuses.A, Fuse-Block with plain Wire Fuse.D, Fuse-Block with Mica Fuse in position.
When a fuse burns out in a trolley car or in a light or power circuit, it is because a greater amount of current is trying to pass than the circuit can safely carry. If a fuse were not placed in such a circuit so as to shut the current off before the danger point is reached, any electrical device might become "burned out," or in extreme cases, the wires become so hot as to cause a serious fire.
Figure 98 shows several simple forms of fuses which the experimenter may easily make to protect the batteries, etc., from short circuits.
The simplest possible fuse consists merely of a small piece of lead wire or a strip of thick tinfoil held between two binding-posts mounted upon a wooden block.
The same form of fuse may be made from a strip of mica about two and one-half inches long and one-half an inch wide.
A strip of thin sheet-copper is bent around the ends of the mica strip.
A piece of fuse wire is stretched between the two copper contacts and fastened to each with a drop of solder. Fuse wire of any desired ampere-carrying capacity can be obtained from most electrical supply houses.
Such a fuse is held in a mounting as shown byD. The contacts are made from sheet-copper or brass. They should spring together very tightly, so as to make perfect contact with the copper ends on the mica strip.
Lightning-ArrestersLightning-arresters are used to protect all wires which run into a building from outdoors, especially telegraph or telephone wires, so that static electricity due to lightning will not damage the instruments.Lightning-arresters may be constructed in many ways and of different materials, but there are only two types for which the average experimenter will have any use.Fig. 99.—Lightning-Arrester and Ground-Wire Switch.Fig. 99.—Lightning-Arrester and Ground-Wire Switch.The arrester shown in Figure 99 is the type known as "lightning-arrester and ground-wire switch." It is used principally on telegraph lines.It consists of three pieces of sheet-brass about one-sixteenth of an inch thick, and shaped as shown byA,B, andCin Figure 100.The metal pieces are mounted on a wooden block with a narrow space of about one-thirty-second of an inch separating them.Fig. 100.—Home-made Lightning-Arrester.Fig. 100.—Home-made Lightning-Arrester.The two outside pieces are each fitted with two binding-posts, and the center triangular-shaped piece is fitted with one post.A hole about one-eighth of an inch in diameter is bored between each of the metal pieces.Make a tapered metal pin which can be placed tightly in the holes, and will make contact between the metal pieces.The two outside line wires of the telegraph circuit are connected to the outside metal piecesCandB.Ais connected to the earth or ground.In case of a lightning storm, if the wires become charged, the small space between the metal plates will permit the charge to jump across and pass harmlessly into the ground.If complete protection is desired, it is merely necessary to insert the plug in one of the holes, and thus "ground" either wire or short-circuit both of them.Fig. 101.—Lightning-Arrester for Telephone Wires.Fig. 101.—Lightning-Arrester for Telephone Wires.The lightning-arrester shown in Figure 101 is designed for service on telephone wires. It is an ordinary fuse provided with an arrester in the shape of two carbon blocks about one inch square. The blocks rest on a copper strip, and are held in place by a spring-strip connected toB.The carbon blocks are separated by a piece of thin sheet-mica, of the same size as the blocks.The post,B, is connected to one of the telephone-line wires near the point where it enters the building from outdoors. The post,A, is connected to the instrument;Cis connected to the ground.An arrester of this kind should be connected to each one of the telephone wires.If the line wires should happen to come into contact with a power wire, there is danger of damage to the instruments, but if an arrester is connected in the circuit such an occurrence would be prevented by the blowing out of the fuse. If the lines become charged by lightning, the charge can easily pass over the edge of the mica between the two blocks and into the ground.ELECTRICAL MEASURING INSTRUMENTS
Lightning-arresters are used to protect all wires which run into a building from outdoors, especially telegraph or telephone wires, so that static electricity due to lightning will not damage the instruments.
Lightning-arresters may be constructed in many ways and of different materials, but there are only two types for which the average experimenter will have any use.
Fig. 99.—Lightning-Arrester and Ground-Wire Switch.Fig. 99.—Lightning-Arrester and Ground-Wire Switch.
Fig. 99.—Lightning-Arrester and Ground-Wire Switch.
The arrester shown in Figure 99 is the type known as "lightning-arrester and ground-wire switch." It is used principally on telegraph lines.
It consists of three pieces of sheet-brass about one-sixteenth of an inch thick, and shaped as shown byA,B, andCin Figure 100.
The metal pieces are mounted on a wooden block with a narrow space of about one-thirty-second of an inch separating them.
Fig. 100.—Home-made Lightning-Arrester.Fig. 100.—Home-made Lightning-Arrester.
Fig. 100.—Home-made Lightning-Arrester.
The two outside pieces are each fitted with two binding-posts, and the center triangular-shaped piece is fitted with one post.
A hole about one-eighth of an inch in diameter is bored between each of the metal pieces.
Make a tapered metal pin which can be placed tightly in the holes, and will make contact between the metal pieces.
The two outside line wires of the telegraph circuit are connected to the outside metal piecesCandB.Ais connected to the earth or ground.
In case of a lightning storm, if the wires become charged, the small space between the metal plates will permit the charge to jump across and pass harmlessly into the ground.
If complete protection is desired, it is merely necessary to insert the plug in one of the holes, and thus "ground" either wire or short-circuit both of them.
Fig. 101.—Lightning-Arrester for Telephone Wires.Fig. 101.—Lightning-Arrester for Telephone Wires.
Fig. 101.—Lightning-Arrester for Telephone Wires.
The lightning-arrester shown in Figure 101 is designed for service on telephone wires. It is an ordinary fuse provided with an arrester in the shape of two carbon blocks about one inch square. The blocks rest on a copper strip, and are held in place by a spring-strip connected toB.
The carbon blocks are separated by a piece of thin sheet-mica, of the same size as the blocks.
The post,B, is connected to one of the telephone-line wires near the point where it enters the building from outdoors. The post,A, is connected to the instrument;Cis connected to the ground.
An arrester of this kind should be connected to each one of the telephone wires.
If the line wires should happen to come into contact with a power wire, there is danger of damage to the instruments, but if an arrester is connected in the circuit such an occurrence would be prevented by the blowing out of the fuse. If the lines become charged by lightning, the charge can easily pass over the edge of the mica between the two blocks and into the ground.
ELECTRICAL MEASURING INSTRUMENTS