Hawkins Electrical Guide, Vol 4, by Hawkins And Staff. -- a Project Gutenberg eBook

The trough conduit consists of ducts about 3 inches square made of horizontal boards and vertical partitions, usually of yellow pine about one inch in thickness. This form of conduit can be laid in convenient lengths of 10 or 12 feet, or it can be built along continuously.

Ans. The decay of the wood tends to form acid which corrodes the lead sheath of the cable.

Fig. 979.—Wooden pipe type of conduit. It consists of pieces of wood about 4½ inches square, and three to six feet long, with a wide hole about three inches in diameter, bored through them longitudinally.

Ans. The decay of the wood can be prevented to a certain extent by the application of sterilizing processes, thereby preserving it in fairly good condition for about ten to fifteen years.

Ans. For temporary installations which will be discontinued before the wood decays.

Wooden Built-in Conduits.—Within recent years several forms of wooden built-in conduit have been designed and successfully used for permanent work. They possess several advantages over any of the duct systems, the chief of which are high insulating quality, the capability of using bare wire and rods for underground conductors, and reduced cost. An approved form of wooden built-in conduit is shown in fig. 980.

Fig. 980.—Perspective view of wooden built-in conduit. It consists of an outer rectangular casing of wood which is lined inside with impregnated felt.

Ans. A wooden trough is laid in a trench about 18 inches deep. Porcelain carriers as shown in figs. 981 and 982 are placed in the trough at intervals of 4 to 5 feet, to act as bridgework for supporting the conductors. This bridgework is placed on and is surrounded by impregnated felt or similar material, and the spaces between the carriers, after the conductors have been placed in position on them, is filled with voltax, which hardens rapidly and forms a solid insulating material throughout the conduit.

Wrought Iron or Steel Pipe Conduits.—These are formed of pipes similar to gas or steam pipes, with screw or other connections. They are laid either simply in the earth, or in hydraulic cement, and are the strongest and one of the most satisfactory forms of underground conduit. An appropriate standard of this kind of work is shown in fig. 983.

Figs. 981 and 982.—Porcelain bridgework or carriers for supporting underground conductors.

Ans. A trench, the width of which will depend upon the number of pipes to be laid, is first dug in the ground, and after its bottom has been carefully leveled, is braced with side planking and filled to the depth of two to four inches with a layer of good concrete, consisting of two parts of Rosendale cement, three parts of sand, and five parts of broken stone capable of passing through a one and one-half inch mesh. This concrete is well secured in place and forms the bed for the lowermost layer or tier of pipes. Ordinary wrought iron pipe is employed, in 20 foot lengths about three to four inches in diameter, depending upon the size and number of cables they are intended to carry. After the last tier of pipes have been put in place, and a layer of concrete from two to four inches placed over it, a layer of two inch yellow pine planking is laid over the whole.

Fig. 983.—Cross section of wrought iron pipe conduit laid in hydraulic cement.

Ans. To protect the conduit against the tools of workmen making later excavations.

Ans. Pipe lined with cement. The internal surfaces of these pipes are usually covered with a lining of pure Rosendale cement about ⅝ inch thick and containing no sand. The internal surface of the cement lining does not offer much friction to the introduction or withdrawal of the conductors.

Cast Iron Pipe and Trough Conduit.—Cast iron pipe for underground conduits is similar to ordinary wrought iron pipe, except that it is thicker. The additional thickness is necessary to make the strength equal to that of wrought iron; it is therefore heavier to handle and more expensive.

Ans. It consists of shallow troughs of cast iron in six foot lengths, laid directly in the earth so as to form a system of continuous troughing in which the conductors are placed and then covered over by cast iron covers which are bolted to the trough.

Ans. First, the cables can be laid directly in place, thus eliminating any chance of injury during the process of drawing in, and second, the cables are easily accessible at any point by simply removing one or two of the sectional cast iron covers, thus permitting of their being readily inspected and repaired.

Fig. 984.—Fibre conduit. It consists of pipes made of wood pulp, having about the same thickness as cast iron pipe. Slip joint conduit for electrical subways is three inches inside diameter. The socket joints keep the lengths centered and make it easier to lay than a mere butt joint. It is laid in cement like iron pipe.

Fibre Conduits.—This form of conduit consists of pipes made of wood pulp impregnated with a bituminous preservative and insulating compound. These pipes are laid in concrete in a manner similar to iron pipe. Fibre conduits are made in sizes ranging from 1 inch to 4 inches in diameter and from 2½ to 5 feet in length, with walls ranging from ¼ to ½ inch in thickness.

Ans. The socket joint type, as shown in fig. 984, the sleeve type, fig. 985, and the screw joint type, fig. 986.

Ques. What is the usual method of laying the socket joint type of fibre conduit?

Ans. After the trench has been dug to the required width and depth, depending upon the number or pipes to be placed in a tier and the number of tiers, a bed of concrete about 3 inches deep is placed on the bottom and a line drawn on one side for the alignment of the first line of pipes. The other lines of pipe or ducts are laid parallel to the first line, and are separated from it and from each other by means of ¼ inch or ½ inch wooden or iron pegs. The pipes are well grouted and covered with a layer of concrete to the depth of ¼ or ½ inch, and the next tier laid in place in the same manner. When the final tier of pipes has been installed, it is covered with a layer of concrete about 2 to 3 inches deep.

Fig. 985.—Sleeve joint type of fibre. Both the socket type (fig. 984), and the sleeve type here shown are easily aligned without the use of a mandrel.

Ques. What is done when it is necessary to cut a length of pipe to break joints, or to enter a manhole?

Ans. The remaining part of the length may be utilized by using a fibre conduit sleeve having an inside diameter ½ inch greater than the pipe being used on the system.

Fig. 986.—Screw joint type of fibre conduit. This method of connection will form a tight line and is suitable for running under the lawns of private houses and parks, under the streets of towns and villages, and in other places where the cost of building electric subways is prohibitive.

Edison Tube System.—Of the various built in or solid underground conduit systems other than those already described under wooden conduit systems, the most satisfactory are the Edison tube system, the Crompton naked conductor system, the Kennedy system, which is a modification of the Crompton and the Callender systems.

Ans. It consists of a series of iron tubes or pipes containing one or more copper conductors which are placed therein before each complete section or pipe leaves the factory, so that they only need to be joined together to form a continuous line of underground conduit with conductors in place. The arrangement of wires and the details of the Edison tube system are shown in figs. 987 to 989.

Fig. 987.—Cross section of Edison "feeder" tube. This runs from the power station to the centers of distribution, and contains two principal conductors and a smaller conductor to serve as a neutral wire, and also three insulated cables of seven strands of No. 19 B. W. G. wire each. These cables form independent circuits and enable the voltages at the distant end of the feeder to be read at the central station. For this reason they are commonly called pressure wires.

Underground Cables.—Electric light and power cables for use in conduit may be divided into two classes: moisture proof, and non-moisture proof, according to the character of the insulator. In the moisture proof cables, the insulation consists of some form of rubber, or of bitumen, and a metal sheath or covering, usually of lead, is provided to protect the cable from mechanical or chemical injuries. The non-moisture proof cables are insulated with paper impregnated with oil, wax, or resinous compounds.

Fig. 988.—Cross section of Edison "main" tube. A number of these tubes, which radiate from the center of distribution and loop the ends of the feeders together, have three conductors of the same size. These tubes are placed in the ground so as to bring the positive and negative conductors on one side of the center of the tube, and the neutral conductor on the other side. The mains are always laid with the neutral conductor adjacent to the curb line, and for convenience this side of the tube is commonly called the inside. The feeders are always laid with the positive conductor on the right hand side, as shown in fig. 989.

Metal Sheaths on Underground Cables.—Metal sheaths are used on rubber covered cables to protect the insulating compounds from the deteriorating effects of electrolysis and various kinds of acids and gases which, under present methods of construction, are ever present in the underground conduits. It is a fact, however, that the lead sheath on a low tension cable, which is used as one side of a grounded circuit, has been, in some cases the cause of, instead of, cure for electrolysis. The proper cure lies in the omission of the sheath altogether, but as this is not practical except in the case of very large conductors, the best thing that can be done is to interrupt the continuity of the sheath by some form of insulating joint.

Fig. 989.—Method of laying Edison underground tube system. The tubes are laid in trenches about 30 inches deep and 20 inches wide at the bottom, each trench usually containing two lines of pipes—a main adjacent to the curb and a feeder on the outside. The copper rods forming the conductors are uniformly 20 feet, 4 inches in length and project from 2 to 3½ inches from each end of the pipes, which are connected together by means of coupling boxes. The coupling box usually employed consists of a two part egg shaped casting into which the ends of the pipes enter through water tight sleeves at the opposite ends of the oval. The projecting ends of the copper conductors are joined by short pieces of flexible cable with sockets on each end, which are drilled to fit easily over the conductor rods to which they are thoroughly soldered in order to make a perfect electrical joint. After the conductors have been thus properly connected the cover is bolted down on the lower half, and the whole of the interior of the box is filled with insulating compound through the small hole at the top of the cover, thereby completely insulating the copper conductors, the cable connectors, and the ends of the tubes. Finally, the hole in the cover is closed with a cast iron cap. These coupling boxes are also made in the form of tees for making branch connections, and in the form of elbows for turning corners, the ball ends attached to the tubes and the sockets into which they fit being designed to permit of variation in direction through an arc of 18 degrees on either side of the central position. Services or branches to the consumers' premises consist of short lengths of tube which tap the mains by means of three way or four way service boxes, the latter readily permitting the taking of two services from one joint. Services are never taken from the feeders, but the latter are brought to distributing boxes containing three copper rings to which the conductors are connected and branched out to one or more mains which are led out through fuses to supply the districts.

Pot Heads.—The upper end of a lateral cable is equipped with a discharge bell, which is commonly called a pot head. The purpose of a pot head is to hermetically seal the end of the cable and bring the conductors out in such a manner as to permit of their being conveniently connected to the primary service boxes.

Fig. 990.—Bottom of General Electric manhole junction box; view from manhole interior. The cables enter the bottom of the box as shown through composition nozzles to which the lead sheathes are united by a wiped solder connection, forming a permanent water and gas tight joint. Stuffing boxes are sometimes substituted, doing away with the wiped joint, rendering the boxes suitable for use with unleaded or braided cables. The normal position of the distributing cables is in the upper ducts so that they may be brought to the junction box without crossing other lines. The entrance nozzles and seats are so arranged that all terminals are soldered to cables outside of box and any cable may be removed without disturbing any soldered joint. The wiped joints unite electrically the lead sheathes of all cables entering the box and by connecting a single earth bond to the shell of the box all cable sheathes are solidly grounded. Incombustible shields prevent the arc from a blown fuse making a ground connection to the shell or inner cover.

Ans. They are usually made in three parts, the base being of cast brass, having a diameter depending upon the size of the conductors, with a hole in the lower end threaded within in such a manner as to make a tight fit on the cable.

Ans. After the cable has been bent in to the proper position, the brass base is slipped down over it with the larger end up, and then screwed down on the lead sheath. The threads cut down into the lead sheath to a distance of about ½ inch along the sheath, thus making an air tight connection without necessitating the making of a wiped joint.

CHAPTER XLI
WIRING OF BUILDINGS

In laying out the circuits for a dwelling house, the cut out cabinets should be located first. In many houses only one cut out cabinet is necessary, but in large houses it is convenient to have one on each floor, with vertical mains running through them from the top to the bottom of the house.

If only one distributing point be used, it should be either in the cellar or attic and risers run to the different floors.

Ans. They should be installed near a partition that is so located as to make the running of risers easy, and should be on an inside wall to guard against dampness.

Ques. What instructions are usually given the electrician who does the wiring?

Ans. In many cases simply a plan showing the location and number of lights, from which he must figure out how to install them using the least amount of material and labor consistent with a good installation that will pass inspection.

Ques. What provision should be made in rooms where lamps are suspended from the ceiling?

Ans. A switch should be placed at a point where it will be convenient for any one entering to turn on the light.

Fig. 991.—Ceiling button. If a lamp be needed not more than 3 feet from the direct line of the wires, it can be hung where required by means of a ceiling button, as shown in the figure, but the lamp cord must not be used to run lamps in this way more than two or three feet from the rosette.

Ans. The switching arrangement should be so designed that the lights may be turned on or off either from the hall or floor above.

Fig. 992.—Two way lighting circuit permitting control from two points. This is the usual arrangement for hall when it is desired that the lights may be turned on or off from either floor. The circuit contains two two way switches connected by "travellers." From the diagram it is seen that the light may be controlled from either switch. It is a bad arrangement to have travellers and return wire located near each other, as it is possible by this method to connect two individual circuits together and possibly overload one of the two feed wires of each circuit. However, should each feed wire run to a fuse direct, without any other lamps than those contained in the three way circuit being connected, it is not objectionable and becomes a convenient method in many cases.

Fig. 993.—Four way lighting circuit, permitting control from three points. This arrangement consists of a four way switch connected between two two way switches as shown. In making the connections it should be noted that the travellers connecting one side of the four way switch to the two way switches should be crossed. On the opposite side of the four way switch, the connections are direct. For the various positions of the switches, the corresponding circuits through them are as follows: ABDGHJ—ABDEIJ—ACFGHJ—ACFEIJ.

Ans. By the use of a 4 way switch and two 2 way switches connected as shown in fig. 993.

Ques. Before laying out the wiring system for a building, what should be done?

Ans. It is necessary to ascertain whether power will be supplied from the central station, or whether a private plant is to be installed.

Fig. 994.—Two wire multiple system as used with isolated plant.

Ques. When the central station is to supply power as an auxiliary in case of break down, how should the connection be made?

Ans. The supply from the central station should be connected to the wiring system through a double throw switch, as in fig. 995, so that either source may be thrown into circuit.

Ques. How are the connections made when the auxiliary supply is brought in through a three wire system?

Fig. 995.—Double throw switch for use in isolated plants when auxiliary power is used from the central station in case of breakdown.

Ques. When power from an outside source only is to be used what must be determined before wiring?

Ans. The system of wiring of the supply. If a three wire system be used, the general arrangement will be as shown in fig. 997.

Fig. 996.—Double throw three pole switch for use in isolated plants where auxiliary power is brought in through three wire system. The side of the switch controlling the current is bridged as shown.

Ques. Would it be expensive to change a regular three wire system to a two wire system?

Ans. It would require the reinforcement of all mains and feeders by an additional wire. This wire would be connected with the neutral wire so as to make the capacity of the neutral equal to the sum of the other two. If a three wire two wire system had been originally installed, no change in the wiring system would be necessary. The only change would be at the service end of the switchboard, and the doubling of the size of the center fuses.

Fig. 997.—Three wire convertible, or three wire two wire system; used to advantage where power is supplied from an outside source and brought in through the three wire system. The only difference between the three wire convertible, and the straight three wire system is that the center, or neutral, wire of the mains and feeders should have a current capacity equal to the other two. The reason for this is that it allows the system to be readily changed over to a two wire system for use in connection with a private plant. It sometimes happens that after using power from the local electric illuminating company for some time, conditions arise which make it expedient for the owners to install a private electric plant. If a straight three wire system had been originally installed, the mains and the feeders when used on a two wire system would not be heavy enough by 25 per cent., as the neutral wire of a straight three wire system is the same in size as one of the two outer wires, and theoretically carries one-half the current or less.

Ans. It is more expensive to install than one for a two wire system, as it is necessary to add a balancer in connection with a 240 volt dynamo. This balancer set should have one-tenth the capacity of the plant. Such an equipment has its advantages when 240 volt motors and 120 volt lamps are connected to the system. With this plant no changes in the motors are necessary, whereas in a straight 120 volt system, the motors would have to be changed from 240 to 120 volt machines.

Fig. 998.—Diagram showing reinforcement of neutral wire necessary to change regular three wire system to two wire system. The capacity of the neutral wire must equal that of the sum of the two other wires.

Ques. After deciding on the system of wiring to be used, how should the electrician proceed with the work?

Ans. He should lay out the mains, feeders and branches of the wiring system. The outlets are first located and then the distributing centers. There is no fixed rule or plan by which to go, but the current density and source of supply are the main points to be considered in locating these centers. He must also consider the construction of the building and select runways and shafts which provide easy runs for feeders.

Ans. Panel boards in loft buildings or in any building requiring 8 to 10 circuits to a floor should be distributed one to a floor. In private houses it is sometimes advisable to install only one panel for the entire house. This is good practice for a three-story house not requiring over twelve circuits.

Fig. 999.—Diagram showing current required on each floor of building. A sketch of this kind is useful in laying out the feeder system. In the building here shown it will be seen that the basement and first floor require the most power. In such a case a feeder is run for these floors, and a sub-feeder from the basement to the first floor. It is not worth while to reduce the size of the sub-feeder unless the amount of current used on the sub-feeder be a small percentage of that used in the feeder. Another reason is that in changing the size of a wire, the underwriters require a fuse to be inserted. This makes it necessary to install a larger panel with larger trim, etc., and the consequent expense easily offsets any gain made by installing a smaller wire.

Ques. How should the arrangement of feeders for a large building be determined?

Ans. A good method is to draw an elevation of the building as in fig. 999, and note on each floor the current requirements.

Fig. 1,000.—Diagram showing arrangement of switches in wiring system where provision is made that any circuit can be fed from an outside source in case of overload or accident.

Ans. Feeders requiring over 2 inch pipe should not be used. It is better to subdivide them, especially if there be many bends or offsets, since two inch pipe is about the limiting size for economical handling.

Ans. They should radiate from a distributing panel, having a proper sized switch and fuse for each feeder.

Fig. 1,001.—Sectional view showing method of cutting a pocket or opening in floor for the insertion of wires.

Ans. It is advisable to install them in iron pipe even though the circuit wires be run otherwise. Since the former carry the main supply of current it is important to have them well protected as they usually run up side walls.

Ans. In laying out the branch circuits, it is not good practice to use up the underwriters' circuit allowance of 660 watts.

Fig. 1,002.—View of outlet pocket showing base board, and cover supports in position.

Ques. If concealed wiring is to be installed in a finished building what should be done first?

Ans. The outlets should be marked on the ceilings and walls with a pencil cross at the spot, marking also the location of switches, etc.

Ques. If an outlet is to be placed at the center of a room, how is the center of the ceiling located?

Ans. It is first located on the floor, then transferred to the ceiling by means of a plumb bob.

Ans. A small hole is bored through the ceiling and the bit pushed up till it comes in contact with the flooring of the room above, this flooring is also bored, as in fig. 1,001.

Fig. 1,003.—View of completed pocket and ceiling outlet showing method of bringing out the wires.

Ans. One-quarter inch holes are bored to insert a keyhole saw through the joint between two boards at each end of the pocket, and as near the beams as possible, then the board is cut at an angle as indicated in fig. 1,001. Having sawed across the board at both ends, it is pried out with a chisel as shown.

Ans. They are bored about two inches from the top with a ⁹/₁₆ inch bit, slanting downward just enough to give clearance for the brace.

Fig. 1,004.—Device for examining partition interiors. A pocket flash lamp and a little mirror are the only apparatus required to inspect the interior of a wall or partition which would ordinarily be inaccessible. For fishing wires, retrieving cable and inspecting finished work, the lamp and mirror will be found most useful. The mirror has only to be introduced in the outlet hole in the wall, the flash lamp and eye being held behind it as illustrated. The mirror reflects the light of the lamp onto the place to be illuminated, at the same time reflecting the image back to the eye near the lamp. The usefulness of this little device is as great as its simplicity.

Ans. Screws may be used but stout wire nails are satisfactory and are inserted with less labor.

Ques. How is a ceiling outlet completed after the work has reached the stage shown in fig. 1,002?

Ans. A baseboard is next installed as in fig. 1,003 to have a secure hold for the screws used in fastening the fixtures. Two holes are then bored diagonally with a ¹¹/₁₆ inch bit inserting the bit in the small hole bored in the ceiling as in fig. 1,001. The outlet wires are then tied around the knobs and the upper ends being bared and tapped on to the main wire. A piece of loom is slipped on each outlet wire after which it is thrust through the outlet as in fig. 1,003.

Fig. 1,005.—Plan showing one floor of a dwelling house wired with conduits. The numbers on the various outlets indicate the number of lamps supplied. The wiring is carried out on the loop system, and it will be noticed that no branches are taken off between outlets. Four circuits are used in order that there may not be more than ten lamps on any one circuit.

Ans. By taking a turn around the intermediate knobs and a dead end hitch at the end knobs, or they may be hitched at each knob. The main may be secured also by use of a tie wire.

Ans. A splice is the joining of two wires at their ends; a tap is the joining of the end of one wire with an intermediate point of another wire.

Fig. 1,006.—Wiring for heating appliances in two story house; plan of basement.

Ans. All wires joined together should be soldered as this insures good electrical contact.

Ans. They should be covered with rubber tape twisted tightly while it is hot. When the rubber has melted it will adhere to the joint and can be moulded with the fingers. Adhesive tape is then wound over the rubber, the insulation thus being made equal to that which was removed to unite the wires.

Fig. 1,007.—Wiring for heating appliances; plan of first floor.

Wiring for Heating Appliances.—There are now on the market a great number of heating appliances which absorb such small amounts of energy that they can be used readily on the lighting circuit. These appliances include the coffee percolator, chafing dish, heating pad, small water heater, cigar lighter and many other miscellaneous devices. By adapting these smaller devices to the lighting circuit, not only is the cost of wiring decreased, but the convenience and cleanliness of the electrical system is secured.

CHAPTER XLI WIRING OF BUILDINGS

CHAPTER XLI
WIRING OF BUILDINGS