* UNIVERSITY OF CALIFORNIA COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION BERKELEY, CALIFORNIA MAINTENANCE OF FARM ELECTRIC WIRING J. R. TAVERNETTI' Natural wear, deterioration, accidents, misuse, improper equipment, and faulty workmanship make necessary a certain amount of repair and main- tenance on farm wiring systems. While ordinarily this repair and maintenance is not great, con- siderable trouble and expense may be saved if it is done before failure or accidents occur. Al- though the average farmer is not an electrician, and should not attempt to do major electrical work, usually he is capable of making minor addi- tions and repairs which would contribute to safety from shock, accidental operation of ma- chines, failure of equipment, breakdowns in the wiring, and to lessen fire hazards due to short circuits, overloading, and improper protection. Electricity must always return to its source, or in other words, must make a complete circuit. The wiring system provides a path for the current to flow to and from the appliances being used, and is made up of two main parts: the conductors (usually copper) through which the current flows, and the insulators (rubber, porcelain, glass, etc.) which keep the electricity within the con- ductor and prevent it from taking an unintended path. It is also equipped with switches for turning the electricity on and off, outlets for connecting appliances, and fuses for protection against overloads (fig. l) . ELECTRICAL TERMS In order to care for and use appliances and wiring materials properly, it is necessary to understand the meaning of certain electrical terms and their use in connection with electric circuits and equipment. Volt : The volt is the unit of electrical pres- sure; and the voltage is the force that causes the electric current to flow. The common voltages supplied to farms by power companies are 115 (110 to 120) and 230 (220 to 240). On some farms only 115 volts are available, while on other farms both 115 and 230 are supplied. Irrigation-pump motors are generally made for 230 volts, although, some are 460 volts. Appliance equipment such as mo- tors, heaters, and lights are designed to be operated on a given voltage which is generally written on them. Some motors and heaters have two voltages on the name plate which means that they can be operated on either; but they must be Associate Agricultural Engineer in the Experiment Station. connected in a different way for each voltage which is given in the set of instructions or on the name plate. Wiring equipment such as switches, outlets, fuses, and wire usually have a voltage marked on them which is the maximum for which they should be used. Ampere : The ampere is the unit for the rate of flow of electric current. The number of amperes flowing in the wiring system is determined by the appliances being used. Each appliance has a given resistance in its wires which limits the amount of current (amperes) that will flow through it. In the case of a short circuit--that is when the current does not flow through an appliance — the only resistance limiting the amount of current is that in the wiring system. This resistance is very low causing a large current flow; this re- sults in overloading and burning out of fuses. The sizes of fuses are rated according to the num- ber of amperes they will carry without burning out . When current flows through wires and wiring de- vices, heat is generated, the amount depending on their size and the amperage. If too much current goes through they overheat, causing injury to the insulation and sometimes fires; also there is wast- ing of electricity. Table 1 gives the safe loads for various sizes of wires commonly used on farms. Switches, outlets, plugs, and sockets usually have the maximum amperes or watts for which they should be used marked on them. Watt : Watt is the unit for electric power and is used as the basis for rating the sizes of lamps and heaters. The watts are equal to the volts times amperes. A kilowatt is 1,000 watts and is equivalent to 1 1/3 horsepower. Phase : Two types of electric service, single- phase and three-phase are supplied to farms. Single-phase service requires only two wires and is the type supplied for the home and general use. Three-phase service requires three wires and is the type supplied for irrigation and other motors over 5 horsepower. Three-phase service should not be confused with dual voltage (115 and 230), single-phase service which also requires three wires. Single-phase current can be obtained from three-phase by using any two wires, but three- phase can never be obtained from single-phase. Ground : A ground is an electrical connection with the earth, usually made by connecting to a water pipe or to a metal rod or pipe driven at least 8 feet into the soil. There are two types [1] UNIVETvS!TY OF CALIFORNIA '?ARY COLLEGE OF AGRICULTURE DAVIS TABLE 1 Maximum Safe Capacity, and Length of Rubber-Covered Copper Wires That Will Maintain Voltage Drop Within Five Per Cent Maximum Maximum Maximum allow- Wire carrying allowable able length of gauge capacity, load in wire in feet no . amperes watts, with with full load 115 volts on 115 volts* 18t 3 345 250 16t 6 690 200 14* 15 1,725 125 12 20 2,300 150 10 25 2,875 200 8 35 4,025 225 6 50 5,750 250 4 70 8,050 275 *Since two wires are necessary, the distance from the source of current to the load would be half of the length. For loads less than the maxi- mum, the length can be increased in the same pro- portion as the decrease in load. For example, if the load is only two thirds of the maximum, the length can be multiplied by 3/2. With 230 volts, the maximum load and length can be doubled. TUsed only for lamp and appliance cords. ^Minimum size for permanent wiring. of grounds used. One is when the frame of a piece of electric equipment or the housing for a switch is connected to the earth, and is for pro- tection against shock in case the frame or hous- ing becomes shorted to the electric circuit. The other type of ground is when one of the wires forming the electric circuit is connected to the earth, and is for protection of the wiring system against lightning and breakdowns in the trans- former. This ground is always made at the transformer and is now required to be made also at the main switch. Neutral and Live Legs : The wire which is grounded is known as the "neutral" or "grounded" leg of the circuit while the other wire is known as the live or "hot" leg. In properly installed wiring, the two legs are identified by using dif- ferent-colored wires — usually white for the neutral wire, and black for the live wire. Fuses and switches should always be installed in the live leg (fig. 1) . Voltage Drop: Voltage drop is the loss in voltage between the source of the current and the appliance being used. It is the electrical pres- sure lost in overcoming the resistance of the wires, and its magnitude depends on the number of amperes flowing and the size and length of the wires. The voltage drop is not great in short wires if the current is within the safe limit, but may be sufficient in long wires, even if the load is within the safe limit, to have consider- able effect on the operation of appliances. For example, the voltage at the source is 115, but the voltage at the appliance is only 105 with the re- sult that lamps give out less light, heating de- vices do not develop sufficient heat, and motors do not develop their rated power. Table 1 gives the maximum length of wires of various sizes that can be used to keep the voltage drop within 5 per cent of that at the source. CARE OF OUTSIDE WIRING 1. Outside wiring should be securely fastened on the ends to strain insulators which are at- tached to the solid part of a building, such as the framework, or to poles which are sufficiently strong or supported by guy wires or braces to stand the pull. 2. The wires should be at least 6 inches apart and preferably farther, and should be securely fastened to the insulators and not allowed to touch anything but insulators. Tree branches should be trimmed away from the wire, and anything that might fall on them eliminated. 3. Excess sagging should be eliminated by proper tension and support (usually every 100 to 125 feet) and sufficient clearance allowed over driveways (16 feet) and walks (12 feet). 4. Insulators should be of the outdoor type made of glazed porcelain or glass (fig. 2). Split Fig. 1.--A typical branch electric circuit showing fuse block, insulators, outlets, and switch. The white wire is the grounded or neu- tral leg, and the black wire is the "hot" or live leg. Fuses and switches should be in the "hot" leg. Fig. 2. --Various kinds of glazed-porcelain in- sulators suitable for outdoor use. A, Solid knob used for intermediate supports. J3, Spool-type strain. C, Screw-type strain for attaching ends of wires. [2] knobs should never be used outside as they are not moistureproof , and because they may work loose and allow the wire to become disconnected or to wear off the insulation. 5. Fixtures such as sockets and switches should be of the weatherproof type or should be so en- closed as to protect them from moisture. Water is a conductor of electricity and may cause a short circuit. 6. All joints and connections should be tight, and tapping the wires for branch circuits should be done near a support and not in the middle of a span where it puts an extra strain on the wires. CARE OF INSIDE WIRING 1. Excess wire should be eliminated and the es- sential wiring kept tight and supported by insu- lators at least every 4| feet. 2. Exposed wires should be kept at least 2 s inches apart, and should have extra insulation of porcelain tubes or loom over them when crossed and where run through walls or into fixture boxes (fig. 1). 3. Fixtures such as outlets, switches, etc. , should be securely fastened to a solid support. 4. Conduit and flexible cables should be fas- tened to junction, outlet, and switch boxes so that they are held by the mechanical protection and not by the c.onductors (fig. 3). 5. Broken insulation and damaged or worn fix- tures should be repaired or replaced (fig. 4). There is always danger of receiving a shock from^ exposed conductors while the failure of a fixture when needed may cause considerable delay and ex- tra work. 6. Fixtures or equipment from which a shock is received should never be used until the trouble is remedied. The next shock may result in serious injury or death. Switch boxes, conduit, covered cables, and motor frames should be grounded. 7. Where wires or fixtures may be exposed to mechanical injury from accidents they should be given extra protection. A board nailed over or alongside of wires or fixtures may keep them from being hit by tools or otherwise. 8. Wires and fixtures should never be used to hang things on or as a support for resting tools, lumber, or other materials. 9. All splices and connections should be tight (fig. 5). A loose connection may cause overheating at the connection and may also re- sult in fluctuating voltage which causes lights to flicker, and uneven motor operation. Screws on switches or other connections should be kept tight with care being taken not to strip the threads. Fuse holders and switch contacts should be tight. I C Fig. 3. --Conduit and flexible cables should be securely fastened by lock nuts and connectors to a junction, outlet, or switch boxes, and should be supported at intervals by straps. Fig. 4. — Damaged and worn wires and fixtures are dangerous and unreliable and should be re- placed or repaired. [3] Fig. 5- --Types and methods of wire splicing: A, Rattail splice used in joining wires in junc- tion and outlet boxes; B, tap splice used in con- necting branch lines; C, Western Union splice used when splice is under tension. In making splices, the wires should be scraped clean, twisted tightly together and soldered, as at D, then covered with rubber insulating tape (E) , and then with friction tape (F) . 10. All wiring, fixtures, and switches should be kept clean of dirt, spider webs, wasp nests or other matter. Such foreign material not only may interfere with the operation, but may cause a short circuit, particularly if wet. 11. -Switches should be set so that they can- not accidentally go on in case they become loose; they should be within easy reach in case it is necessary to turn them off in a hurry; they should be easily turned on and off without expos- ing the operator to the danger of contacting the current -carrying parts; and they should be out of the reach of small children. Knife switches should be turned on and off with a quick movement to decrease burning of the contacts. 12. Extra fuses, plugs, sockets, insulators, friction and rubber tape, and a test lamp (fig. 7) should be kept on hand at all times. CARE OF PORTABLE CORDS 1. Mechanical injury to cords can be lessened by keeping them away from heat and moisture, by not hanging them over nails and pipes, by not running them under rugs or on floors where they will be stepped on, by not running them through doors or windows where they may be squeezed, and by not subjecting them to unnecessary bending and twisting. 2. In removing the plug from an outlet, one should take hold of the plug and not pull on the cord. 3. Cords should be checked occasionally for broken insulation, plugs, or sockets, and the damaged parts repaired or replaced (fig. 4). The points that should be especially checked are where the cord enters the plug, socket, or appliance, as these places receive the most wear and bending. 4. Silk- or cotton-covered cords, or cords with brass-shelled sockets should not be used outdoors or in moist locations; rubber-covered cords with weatherproof sockets should be used instead. 5. Plugs should fit tightly, as a loose fit not only allows the cord to become disconnected easily but causes excess heating at this point. Bending the prongs of the plug outward helps to make a good connect ion. 6. Cords and the connections for them are not designed for carrying heavy loads and care should be taken not to overload them (table l) . If the cord or the connections feel extra warm to the touch, it is a sign of overload. Particular care should be exercised in the use of double and triple sockets (fig. 6). 7. Cords should never be used for permanent wiring. SOME "DON'TS" THAT SHOULD BE REMEMBERED 1. Don't touch broken wires or the current- carrying parts of an electric circuit unless you know the current is off and the line dead. 2. Don't attempt to repair wiring or equipment without opening the switch ahead of it or remov- ing the equipment from the line. 3. Don't touch equipment or fixtures with wet hands, or when standing in water or touching plumbing. 4. Don't try to change fuses in the dark or use more than one hand in changing them. 5. Don't use substitutes for fuses or replace a fuse until the cause of its blowing has been fixed or removed from the line. 6. Don't use equipment or fixtures from which an electric shock has been received until the trouble is remedied. 7. Don't use electricity for experimenting or for practical jokes. 8. Don't take a chance on using wiring, fix- tures, or equipment unless you know they are suit- able for the job. Obtain advice and help from the power company, or from an electric contractor or dealer. Fig. 6. --The use of double and triple sockets is a dangerous practice. The socket and con- necting cord are designed for light loads (usu- ally less than 300 watts) and overloading not only causes excess heating, but also a drop in voltage which affects the operation of appliances, Fig. 7- — A test lamp consisting of a weatherproof socket and an ordinary lamp is an inexpensive and convenient device for checking electric circuits. On farms where both 115- and 230-volt power is used, the lamp should be a 230-volt so that it can be used on either voltage; on 115 volts, it will burn with a dim yellowish-red light while on 230 volts it will burn with full brightness. A, Method of checking a portable cord; the leads of the lamp are inserted in the slots of the plug. B, Method of checking for current at a switch; a lead is touched to each leg of the circuit ahead of the fuses. C, Method of checking for blown- out fuse. One lead is touched to the cir- cuit behind the fuse to be checked while the other is touched to the other leg ahead of the other fuse. 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