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Trouble shooting electrical problems
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- 1 PREVENTATIVE MAINTENANCE
- 2 PLANNING REQUIREMENTS, PROJECT MAINTENANCE, TROUBLE SHOOTING
- 3 PRECAUTIONS
- 4 SYMPTOMS OF ELECTRICAL TROUBLE
- 5 NO VOLTAGE
- 6 FUSES KEEP BLOWING
- 7 LIGHTS GROW DIM
- 8 LIGHTS BURN BRIGHTLY, BUT BURN OUT
- 9 LIGHTS FLICKER, MOTORS RUN UNEVENLY
- 10 CONNECTIONS GET HOT
- 11 SHOCKS WHEN TOUCHING EQUIPMENT
- 12 MOTORS RUN IN REVERSE OR WILL NOT START
- 13 LOCATION AND TYPE OF FAULT
- 14 TEST EQUIPMENT
- 15 TEST LAMPS
- 16 VOLTAGE TEST
- 17 DETERMINE GROUNDED OR UNGROUNDED LINES
- 18 DETERMINE A DOWN FUSE
- 19 CONTINUITY TESTER
- 20 METERS
- 21 TROUBLE CORRECTION
- 22 FUSE REPLACEMENT
- 23 PREVENTATIVE MAINTENANCE
- 24 PERIODIC VISUAL INSPECTION
A well installed electrical system is relatively trouble free. But troubles arise. A sound preventative maintenance program will reduce the amount of failure. This section covers the basic elements of a preventative maintenance program. It also covers the elements of trouble shooting the problems that do occur.
As the PCVs will stay only two years, the local workers must be trained to perform the maintenance and trouble shooting operations. This section of instruction also describes the preparation of operation manuals to aid the PCVs in this instruction.
The activities of this section stress the learning of trouble shooting techniques. The PCVs cannot effectively teach the local workers if they do not have the skills themselves.
PLANNING REQUIREMENTS, PROJECT MAINTENANCE, TROUBLE SHOOTING
Things can go wrong with an electrical system just as they can with an automobile. Therefore, to keep the electrical system operating after the installation is completed, you must be able to trouble shoot. Trouble shooting has three basic parts. These are: 1. Recognize the existence of trouble. 2. Determine the type and location of the trouble. 3. Correct the trouble.
Always observe the safety rules. Study and memorize the nine safety rules in Section 2 before you start to trouble shoot any electrical difficulty. Also carry with you a sketch of the system with the voltages and currents in each line clearly indicated. You should always know, not guess, how much voltage and current is flowing in a wire before you approach it. Get into the habit of saying to yourself, "This wire should have volts running in it."
SYMPTOMS OF ELECTRICAL TROUBLE
To recognize the existence of trouble in an electrical system, you must be able to recognize the symptoms of trouble. The following are the most common types of trouble in an electrical system.
If the circuit is dead and no current flows there is no voltage. This is usually caused by a blown fuse, loose connection or broken wire. It might also be a failure of the generator.
FUSES KEEP BLOWING
This may be caused by an overload, that is, too many appliances are connected to the circuit, thus drawing too much current. It may be caused by a short circuit, which is a power wire touching a ground or two power wires in contact.
LIGHTS GROW DIM
When the lights grow dim and motors will not start, it usually means that the voltage is lower than it should be. A variety of troubles can cause this problem. There may be a loose connection or an arcing switch. The wiring may be undersized or too long, causing too much voltage drop.
LIGHTS BURN BRIGHTLY, BUT BURN OUT
This usually means that the voltage is too high. Either a generator is not regulated properly or a transformer is improperly connected.
LIGHTS FLICKER, MOTORS RUN UNEVENLY
This may happen when a motor is started. If so it is because the motor draws five times the current while starting than it does while running. While it is starting the voltage drop is five times as great, thus causing the flicker. If the flickering continues after the motor has started ft may be that the motor is improperly grounded. Other causes might be loose connections or too small a transformer.
CONNECTIONS GET HOT
This usually means that the connection is loose and thus creating a high resistance. All electrical connections must be correctly torqued to specifications listed on device.
SHOCKS WHEN TOUCHING EQUIPMENT
This symptom indicates that the appliance or motor has not been properly grounded.
MOTORS RUN IN REVERSE OR WILL NOT START
This occurs in three phase circuits and means that one or more phases are not connected (blown fuse, loose connection, broken wire, etc.) and the motor is said to be "single phasing." Or, this symptom can mean that the connections to the motor have been reversed.
LOCATION AND TYPE OF FAULT
After realizing that the system is not operating properly you still need to determine the type of fault and where this fault is located. These two tasks are accomplished at the same time, The symptom observed gives clues to the type of trouble, but in most cases different faults could produce the same symptom. For example: what is the cause of no voltage? Is a fuse blown, is there a broken wire, is there an open connection, is there a bad switch, transformer, or other piece of equipment, or is there a generator failure? All of these faults could produce the symptom of no voltage. As you locate the fault you are simultaneously finding out what type of fault is present.
A systematic procedure must be used to find the location of the trouble. The design of an electrical system makes this fairly easy. An electrical system is like a tree. From any leaf there of only one stem, one branch, one limb, and one trunk that lead from that leaf to the roots where the energy is received from the soil. Similarly, in an electrical system there is only one branch circuit, one service entrance, one set of secondary lines, one set of distribution lines, and one set of transmission lines that lead from the load to the generator. To locate the fault start from the load that has the symptom and proceed toward the power source. At each convenient point along the system you will need to test to see if the fault exists at that point as well as at the points already checked behind ft. When you find a point where the fault does not exist then work back towards the load testing each point until you find the location of the fault.
To locate the fault in a system you must test the system for the fault at the points successively closer to the power source. There are three pieces of equipment for this testing. They are: 1. Test lamp 2. Continuity tester 3. Meters
There are several types of test lamps that can be used for testing the condition of various electrical circuits. Neon lamps are used in some test lamps and these will glow at any voltage from about 50 volts and UP* Test lamps can be homemade by wiring in series 2 or more-lamp sockets and inserting in each a 110 volt lamp. If 5 or 6 lamps are used, the tester can be used on circuits containing as high as 600 V.
A test lamp can be used to determine if there is a voltage between two wires. If there is electricity lamps will light. The lower the voltage, the dimmer the lamps will be. If two lamps (in series) are placed across 110 volt lines the lamps will each be at half brightness. The same lamps placed across 220 volt lines will each be-at full brightness. Similarly test lamps with 4 lamps or 5 lamps in series can be used to determine when higher voltages are present.
DETERMINE GROUNDED OR UNGROUNDED LINES
After determining that voltage is present, it is useful to know if one of the lines is grounded. Place the test lamp(s) across one of the lines and a known ground. In a properly installed system the boxes or the fuse panel is grounded, or the lamp can be placed across the line and a radiator or other ground. If the test lamp lights the line is ungrounded. If the lamp does not light, the line is either a grounded line or the ground being used to test is not really grounded.
DETERMINE A DOWN FUSE
Fig. 7.1 shows a part of a distribution system, including the layout of a house wiring system. Suppose an appliance connected to outlet 5-A would not operate. With the test lamp touch the ends of the test lamp to the plug contacts. If It lights there ac, power at the outlet and the fault must be in the appliance. If it does not light then there is no power at the outlet and perhaps the fuse is blown. Go to the fuse box and make the following check. With two lamps in series test across the top of fig ? A and B. (Fig. 7.2)
If the lamps do not light then there is no power coming into the house. If they do light test to see if fuse A or fuse B is blown. This is done by placing the lamps across the top of one fuse and the bottom of the fuse to be tested. Fig. 7.3 shows the test for fuse 8.
Fig. 7.3 If the lamps light, then the fuse is good. If the lamps do not light, then the fuse is bad and should be replaced. (See below the procedures to follow when changing a fuse). If the main fuses are good, but there is no voltage at the outlet, test the circuit fuses. Fig. 7.4 shows the test for the fuse protecting circuit #S.
If the lamps do not light then the fuse is blown. If they do light, .they will only be at half brightness, since they are not across the full voltage (220V.) but only across one hot wire and the ground (110 V.). If they do light this indicates that the fuse is good and that there is a loose connection, a broken wire, and open switch or same other fault between the fuse panel and the outlet.
To check a fuse in a three phase circuit, shut down the motors and other loads in the circuit and then test to see that power is present at the fuses. If there is power on all three lines, then check the fuses as described for the main fuses of a house system. Place the test lamp across the top of one fuse and the bottom of another. If the lamp lights the fuse is good. Fig.
7.5 shows the test or fuse B.
Fig. 7.6 shows the construction of a continuity tester. It is made of a bell connected can and batteries. When the leads are connected to the bell will ring. Otherwise nothing will results. 1. Short Circuits 2. Grounded Lines 3. Open Lines
Short Circuits Before making any tests disconnect the power from the lines. A continuity tester must only be used on dead lines. If there is a length of cable that you suspect to be shorted between two of the conductors, follow the following steps. First, at the junction box at one end of the detection of cable direct all the connections of cable. Second, do the same at the other end of the section Third, connect the test leads of the tester across two wires at a time. wires. It will ring when connected to the two shorted Fig. 7.7 shows the connection of a continuity tester to find a shorted line.
Grounded Lines The test for a grounded line is similar to the test for shorted lines. The only difference is the test is made between one of the open lines and a ground.
Open Lines To test to see if a line is open, first disconnect all power from the part of the system that is being tested. Second, at one end of the cable being tested, connect all of the wires together in a fins (but temporary) splice. Third, at the other end of the section of cable connect the continuity tester across two lines at a time. It should ring each time as the circuit is closed at the other end. If it does not ring then one of the two lines is open.
A voltmeter is even better to use than a test lamp for it is able to indicate how much voltage is present rather than just that there is voltage. An ohm meter can be used in place of a continuity tester but most ohmmeters use only a very small current and on longer lengths of line or when testing a poor ground they may not be reliable.
Whenever it is desired to know the amount of current or voltage present at a particular point in the system a meter should be used. It is always safest to disconnect the power when making the connections and then to reconnect the power to take the reading.
When trouble shooting you are only half done when you have located the trouble. You now know why there is trouble and where this is. But you must ask, "why?" If a fuse has blown, this is the reason that there is no power. But, you must ask, "Why did the fuse blow?" If a wire is broken you must ask, "What caused this wire to break?" Before correcting the obvious fault these other faults must be corrected so that the same fuse won't blow again, or the wire break again because the cause was not corrected, The specific corrections for various troubles are readily identifiable. If there is a bad connection, the connection should be opened and remade as if it were the first time it was being made. If there is a bad piece of equipment such as a switch or outlet plug, then this should be replaced. If there is a shorted cable this will need to be replaced or the circuit disconnected and not used. In most cases the skills needed to correct a trouble are the same skills needed for installation of that part of the system.
BEFORE ATTEMPTING TO WORK ON ANY PART OF THE SYSTEM, DISCONNECT THAT PART OF THE SYSTEM FROM THE POWER SOURCE.
Suppose a fuse has blown. Before replacing it check all the outlets on that circuit to see what loads are connected. Total these loads and determine if the circuit is overloaded. If it is overloaded, disconnect some of the loads until the circuit is no longer overloaded. Now open the main switch and replace the fuse that blew with a fuse of the same rating. Close the main switch. If the problem was an overload, it has been corrected. If the fuse blows immediately and the circuit is not overloaded there must be a short circuit either in one of the appliances or else in the wiring of the circuit. Before replacing the fuse again, disconnect all the appliances on the circuit and turn off all the lights. Now replace the fuse by again turning off the main switch, replacing the fuse and turning the main switch on. If the fuse again blows with all the loads disconnected, there is a short circuit in the wiring. Disconnect the .main switch, and using the continuity tester, test to find where the short circuit is. If the fuse does not blow the short circuit is in one of the appliances. Connect the appliances one at a time. If the fuse does not blow when the appliance has been connected, that appliance is good. Disconnect it and try another appliance. Continue this process until the appliance that ha s the short circuit is connected and again blows the fuse. Disconnect this appliance and see that it is discarded or repaired. Now the other appliances may be reconnected and the fuse again replaced, always with a fuse of the same rating as the fuse that blew. That is an example of how the cause was found for the blown fuse, and this can be corrected.
There is actually very little maintenance required by an electrical system. There are only two requirements of a maintenance program. 1. Periodically inspecting the system visually. 2. Performing the required preventative maintenance on all equipment and appliances as specified by the manufacturers.
PERIODIC VISUAL INSPECTION
It is wise to have the entire system inspected twice a year (Once in the fall and once in the spring.) These elements should be inspected at these times.) Poles: Washout at ground line, Rotting at ground line, (Scrape away the earth from around the pole at the ground line to a depth of 2 or 3 inches. Use a short crowbar or hand spike to determine depth to which rot has penetrated.) Hollow rot, (sound body of pole for hollow rot.) Splitting, Effects of lightning, Splitting or pulling of guys, Twisting or raking, Ground wire, (See that the wire is rigidly supported and that it has not been cut or the cross section reduced to any considerable extent by lineman's spurs. See that the connection between ground wire and ground rod has not been weakened by corrosion or mechanical injury.) Grass around base of Role, (All grass, weeds, and any inflammable material should be kept cleared away from the base of the pole for a distance of 2 feet to reduce the fire hazard.)
cross arms: Rotting, Splitting and twisting, (especially on double arms). Loose, broken, or missing pins, Loose or missing braces
Insulators: Cracked: make close inspection for cracks, Chipped or broken or unscrewed Wire, Broken wires, Short circuits, Twisted spans, Loose connections, See that hay wire, the wire etc. is clear of tree twigs, limbs, kite strings, etc.
Liqhtning Arresters (general): Inspect, Graphite, pipe framework (if necessary), supports of arresters and paint, Check gaps. Check horns for loose bolts and position. Inspect for loose ground connection.
Transformers: Inspect for oil leaks. Ground make a mechanical inspection of all former cases, transformer secondary Ground wiring, connections and lightning.
(This page is based on information copied from Rural Electrification Systems prepared for the United States Peace Corps By: Volunteers in Technical Assistance, Inc. (VITA) 3706 Rhode Island Avenue Mt. Rainier., Maryland 20822 USA In accordance with Contract PC 251709 April, 1969.)