A home technician periodically needs to measure circuit parameters. Check what voltage is on this moment on the network, is the cable frayed, etc. For these purposes there are small devices - multimeters. At small sizes and cost, they allow you to measure various electrical parameters. Let's talk about how to use a multimeter further.
External structure and functions
IN Lately specialists and radio amateurs mainly use electronic models of multimeters. This does not mean that switches are not used at all. They are indispensable when electronic devices simply do not work due to strong interference. But in most cases we are dealing with digital models.
There are different modifications of these measuring instruments with different measurement accuracy and different functionality. There are automatic multimeters in which the switch has only a few positions - they select the nature of the measurement (voltage, resistance, current) and the device selects the measurement limits itself. There are models that can be connected to a computer. They transfer measurement data directly to a computer, where they can be saved.
But most home craftsmen use inexpensive models middle class accuracy (with a bit depth of 3.5, which ensures an accuracy of 1%). These are common multimeters dt 830, 831, 832, 833. 834, etc. The last number shows the “freshness” of the modification. Later models have wider functionality, but for home use these new features are not critical. Working with all these models is not much different, so we will talk in general about the techniques and procedures.
Structure of an electronic multimeter
Before using a multimeter, let's study its structure. Electronic models have a small liquid crystal screen on which measurement results are displayed. Below the screen there is a range switch. It rotates around its axis. The part on which the red dot or arrow is marked indicates the current type and range of measurements. There are marks around the switch that indicate the type of measurements and their range.
Below on the case there are sockets for connecting probes. Depending on the model, there are two or three sockets; there are always two probes. One is positive (red), the second negative is black. The black probe is always connected to a connector labeled “COM” or COMMON or that is labeled “ground.” Red - into one of the free slots. If there are always two connectors, no problems arise; if there are three sockets, you need to read the instructions for which measurements to insert the “positive” probe into which socket. In most cases, the red probe is connected to the middle socket. This is how most measurements are carried out. The upper connector is necessary if you are measuring a current of up to 10 A (if more, then also in the middle socket).
There are tester models in which the sockets are located not on the right, but at the bottom (for example, the Resanta DT 181 multimeter or the Hama 00081700 EM393 in the photo). In this case, there is no difference in connection: black to the socket with the inscription “COM”, and red, depending on the situation - when measuring currents from 200 mA to 10 A - to the far right socket, in all other situations - to the middle one.
There are models with four connectors. In this case, there are two sockets for measuring current - one for microcurrents (less than 200 mA), the second for current strength from 200 mA to 10 A. Having understood what is in the device and why, you can begin to figure out how to use a multimeter.
Switch position
The measurement mode depends on the position of the switch. There is a dot at one of its ends, it is usually tinted white or red. This end indicates the current operating mode. In some models, the switch is made in the form of a truncated cone or has one pointed edge. This sharp edge is also a pointer. To make your work easier, you can apply bright paint to this pointing edge. This could be nail polish or some kind of abrasion-resistant paint.
By turning this switch you change the operating mode of the device. If it stands vertically up, the device is turned off. In addition, there are the following provisions:
- V with a wavy line or ACV (to the right of the “off” position) - AC voltage measurement mode;
- A with a straight line - measurement direct current;
- A with a wavy line - determination of alternating current (this mode is not available on all multimeters; it is not present in the photos above);
- V with a straight line or the inscription DCV (to the left of the off position) - for measuring DC voltage;
- Ω - resistance measurement.
There are also provisions for determining the gain of transistors and determining the polarity of diodes. There may be others, but their purpose must be found in the instructions for a specific device.
Measurements
Using an electronic tester is convenient because you don’t have to look for the right scale, count divisions, and determine the readings. They will be displayed on the screen accurate to two decimal places. If the measured value has polarity, then a minus sign will also be displayed. If there is no minus sign, the measurement value is positive.
How to measure resistance with a multimeter
To measure resistance, move the switch to the area indicated by the letter Ω. Select any of the ranges. We apply one probe to one input, the second to the other. The numbers that appear on the display are the resistance of the element you are measuring.
Sometimes what appears on the screen is not numbers. If 0 “jumps out,” then you need to change the measurement range to a smaller one. If the words “ol” or “over” are highlighted, the value is “1”, the range is too small and needs to be increased. That's all the tricks for measuring resistance with a multimeter.
How to measure current
To select a measurement mode, you must first determine whether the current is direct or alternating. There may be problems with measuring AC parameters - this mode is not available on all models. But the procedure is the same regardless of the type of current - only the position of the switch changes.
D.C
So, having decided on the type of current, we set the switch. Next, you need to decide which socket to connect the red probe to. If you don’t even know approximately what values to expect, so as not to accidentally burn the device, it is better to first install the probe in the upper (leftmost in other models) socket, which is labeled “10 A”. If the readings are small - less than 200 mA, move the probe to the middle position.
The situation is exactly the same with the choice of measurement range: first set the maximum range, if it turns out to be too large, switch to the next smaller one. Do this until you see the readings.
To measure current, the device must be connected to an open circuit. The connection diagram is shown in the figure. In this case, it is important to install the red probe on the “+” of the power source and touch the black probe to the next element of the circuit. When measuring, do not forget that there is power, work carefully. Do not touch the bare ends of the probe or circuit components with your hands.
Alternating current
You can try the AC current measurement mode on any load connected to a household electrical outlet and thus determine the current consumed. As in this mode The device must be connected to an open circuit; this may cause difficulties. You can make a special cord for measurements, as in the photo below. There is a plug at one end of the cord, a socket at the other, cut one of the wires, attach two WAGO connectors to the ends. They are good because they also allow you to clamp the probes. After measuring circuit assembled, let's start measuring.
Move the switch to the “alternating current” position, select the measurement limit. Please note that exceeding the limits may damage the device. At best, the fuse will burn out, at worst, the “filling” will be damaged. Therefore, we act according to the scheme proposed above: first we set the maximum limit, then gradually reduce it. (don’t forget about rearranging the probes in the sockets).
Now everything is ready. First, connect the load to the outlet. Can table lamp. We insert the plug into the network. Numbers appear on the screen. This will be the current consumed by the lamp. In the same way, you can measure the current consumption for any device.
Voltage measurement
The voltage can also be variable or constant; accordingly, select the required position. The approach to choosing a range is the same: if you don’t know what to expect, set it to the maximum, gradually switching to a smaller scale. Do not forget to check whether the probes are connected correctly and into the correct sockets.
In this case, the measuring device is connected in parallel. For example, you can measure the battery voltage or regular battery. We set the switch to the DC voltage measurement mode position, since we know the expected value, we select the appropriate scale. Next, use the probes to touch the battery on both sides. The numbers on the screen will be the voltage that this battery produces.
How to use a multimeter to measure AC voltage? Yes, exactly the same. Just choose the right measurement limit.
Testing wires using a multimeter
This operation allows you to check the integrity of the wires. On the scale we find a continuity sign - a schematic representation of the sound (look at the photo, but there is a double mode, or maybe there is only a continuity sign). This image was chosen because if the wire is intact, the device makes a sound.
We put the switch in the desired position, the probes are connected as usual - into the lower and middle sockets. We touch one edge of the conductor with one probe, and the other with the other. If we hear a sound, the wire is intact. In general, as you can see, using a multimeter is not difficult. Everything is easy to remember.
The standard and most common case is when there is no voltage in any outlet or lighting fixture, and sometimes in all of them at once. In this option, there is no choice - it is necessary to test the cable that powers the entire system, and then individual wires.
As a rule, in the distribution boxes of apartment buildings there is a tangle of unmarked and somehow insulated ends. Switches and sockets, especially in old houses, have long outlived their useful life. It is not easy to understand this intricacy and determine the specific place where the circuit break occurred. We have to check all the elements and re-label the cable cores.
Often the work is complicated by the fact that it has to be carried out without turning off the electrical equipment, but for these situations there are various devices and devices produced by industry that allow you to find cliffs even inside walls. But in the conditions of a separate apartment or house wire continuity can be done in simpler ways:
- with a complete power outage using a multimeter;
- or without switching off - with an ordinary light bulb.
Checking wires from light bulbs and batteries
In order to assemble a device for testing wires and cables, it is not necessary to have any knowledge of electronics or radio engineering. No need to understand diodes, resistors or capacitors. Today I will show how to make a wire tester from a regular battery and a light bulb.
So, the need for such a device arose when I disconnected distribution boxes. That is, it was necessary to determine where and where which wire goes.
Of course, when there are two or three wires in the circuit, it is not difficult to determine the direction of the lines in the box, but you must admit that if the wiring is done in dozens of directions, it is extremely not easy to do such work.
One day I was asked to assemble junction boxes. That is, the situation was such that people hired electricians to install electrical wiring. These electricians did some of the work, took money for it, and disappeared somewhere.
Of course, they did most of the work, namely they laid the wires, brought all the ends into the sockets and distribution boxes, and so on in little things, installed spotlights. This is where all their work ended.
All that remained was to install sockets and switches and connect the wires in the junction boxes, which is what they called me for. The customer was in a panic and asked me to finish all the electrical work as soon as possible so that everything would finally work.
The distribution boxes had 8-10 wires per different directions and determining which one is going wrong is easy, especially if you didn’t do the wiring. This is where the need for such a device began how to test wires.
This is a device that consists of a light bulb, a battery, probes and connecting wires between them.
6 Volt light bulb. Initially, the battery was installed on the crown at 9 Volts, but over time it became addicted and I installed four ordinary AA batteries of 1.5 Volts each in its case and connected them in series. That is, in total they also give 6 Volts.
The connecting wires between them are the most common, thin, flexible. It is very important here that their length is sufficient for continuity of wires over long distances.
For ease of measurement, an alligator clip was installed on one end of the probe.
This is convenient in the sense that, for example, the boxes are in different rooms and in order to ring the cable, we attach the crocodile in one box, go to another and check. That is, you can handle this type of work yourself.
Testing a multi-core cable with a multimeter
A multimeter is a simple device that must perform at least the following measurements: constant and variable quantities electrical voltage and current and electrical resistance value.
For testing wires and cables The resistance test function is used. More precisely, in this process it is not the value of resistance that is of interest, but its presence or absence, which shows the state of the circuit being tested.
Before carrying out work, the device switches to the resistance measurement mode in the lowest range of values. Most models of multimeters, if there is a circuit, can produce an audible signal, which significantly increases the convenience of working with the device.
Continuity of cable cores or wires is made as follows:
- if the ends of the wires are at a small distance from each other, then it is enough to connect the probes of the device to them and take a measurement;
- If the area under study is of significant length, it is necessary to short-circuit (connect) all the wires at one end of the cable, and test the wires from the other end by serially connecting the device to each pair of conductors.
If the device does not give any readings at all, then there are two options: either the cable or wire is “broken” completely, or the resistance of the wrong circuit is mistakenly measured.
This should not be confused with when the display shows zero and when there are no numbers on the display at all. When zero is displayed, the circuit is closed but the resistance of the circuit is so low that the readings are close to zero (for example, when continuity of short wires). And when nothing is displayed on the display at all, then no closed circuit(either a mismatch of wire cores, or a break in the wire itself.)
Situations when electricity stops flowing to devices arise quite often and are familiar to any electrician firsthand. There can be a lot of reasons for this, but in most cases the so-called break in the line is to blame. Such a malfunction can only be determined by checking the wire. In this article, together with the site, we will answer the question of how to ring the wires and determine which of the many has suffered damage? In addition, we will talk about how professional electricians determine the location of damage to hidden electrical wiring.
Wire testing device photo
How to ring wires: methods and devices used
Testing wires at home can be done in two ways: using a multimeter and using improvised means such as an ordinary light bulb with a socket. The last option is somewhat inconvenient, but the first is quite simple and accessible for independent implementation. We will consider both options, since sometimes it happens that there is no device at hand, but the result is needed immediately.
Let's start with the first method, which involves using a multimeter. To make it clearer, let’s look at a simple example and use a wire tester to check the integrity of the wire for connection system unit computer to . As a rule, it contains three cores - we will work with them.
How to connect wires photo
We take out a multimeter, turn it on in resistance measurement mode (ohmmeter), close the contact probes and set the indicator arrow to zero. Now let's start testing the cable. We attach one probe to one of the contacts of the plug, and insert the second one in turn into the holes of the connector to connect the cable to the system unit. We observe the indicators of the device, or rather its needle - if the ohmmeter shows the wire resistance within 2-3 Ohms, then the core is in good working order, but if it exceeds 10 Ohms, this is a clear sign that there is a break on this core. It may happen that the multimeter needle does not react at all to your actions - this only means that the contact on the plug and on the connector do not belong to the same core.
How to test wires with a tester
This is the way to test the wires with a multimeter. I would like to note that this testing method is suitable for wires for any purpose - telephone, computer, electrical.
It is not recommended to use the so-called “beeper”, which is equipped with almost all modern multimeters, to determine the integrity of the wire. It operates in the range from zero to several hundred ohms, and it will not be possible to determine the faulty wire with its help.
In almost exactly the same way, you can carry out dialing using a tester equipped with a voltage indicator. It should be understood that no voltage is supplied through a broken wire, and in order to ring the wires with a tester, it is enough to measure the voltage on its wires. On the indicator it should be displayed as identical digital values, which have a different sign (“+” or “-”). The only drawback of this testing method is that the tester is able to determine the parameters of the wire only when it is energized.
Wire continuity photo
Another testing method is suitable for testing exclusively electrical wiring cables - it involves using a piece of ordinary wire with a light bulb. If we are talking about continuity of the lighting circuit, then you can get by with a long piece of single-core wire. The essence of this method is as follows. In the distribution box, the wires leading to one or another consumer of electrical energy are one by one discarded from the general power circuit and instead of them, a separate wire is connected directly to the consumer, the operability of which is beyond doubt. If everything works, then it can be considered faulty. If not, then we restore it to its place and repeat the operation with another wire of the electrical circuit.
In principle, by changing the starting point of connecting the additional wire and using a lamp as an indicator, you can ring almost any section of the apartment wiring. The method is excellent, and most importantly effective - its only drawback is some inconvenience associated with constant switching of wires.
How to test wires with a multimeter photo
Methods for detecting breaks in electrical wiring
We have sorted out the question of how to test the wires with a multimeter; the only question left is how to determine the location of the break? If this question concerns not hidden wiring, but connection cords, then there are few options - the wire probably broke near the plug or plug. But what to do if we are talking about a break in a cable hidden in the wall? How then?
For these purposes, modern industry has developed a lot of devices of the “E-121” type - among professional electricians such a device is called a “woodpecker”. With its help, you can not only determine the location of the electrical wire, but also, if necessary, find the location of its break. Working with it is quite simple - guide it along the cable laid in the wall and watch the special signaling device. At the location of the gust, special electromagnetic anomalies are formed, to which the device reacts by giving an audible signal.
Testing wires with a multimeter photo
There are also so-called old-fashioned methods of detecting hidden and faulty electrical wiring, tested over the years and by more than one generation of radio amateurs. To do this, you will need an ordinary radio receiver tuned to a wave frequency of 100 kHz. When moving it along the electrical wiring, you need to listen extraneous noise– where, in addition to increasing hissing, intense crackling will be heard, there is a wire break.
Now you know how to ring wires, and without the help of a specialist you can easily determine the reason for the lack of electricity in a particular place in the wiring, and, if necessary, locate the location of the break.
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§ 4. CHECKING ELECTRIC CIRCUITS
When using the technological transition “checking electrical circuits”, defects can be detected that lead to the formation of circuits not specified in the diagram or disruption of existing ones (lack of contact, short circuit, break, erroneous connections, etc.). However, it cannot be stated that there are no defects in three-phase circuits and circuits with windings, even if the elements are intact and their connections are correct.
Methods for checking electrical circuits
Electrical circuits are checked in two ways: direct and grounding.
The direct method is distinguished by the absence of auxiliary circuits and is used when the beginning and end of the circuit being tested are located nearby.
The grounding method (Fig. 22), used to test electrical circuits, the beginning and end of which are in different rooms or quite far from each other, is characterized by the use of auxiliary circuits - grounding conductors, cores of any cable, specially laid conductors, grounding bars, etc. To coordinate actions when checking circuits, pre-install telephone communication by using intercoms B1 and B2, connected through the cores of the cable being tested and a common conductor or through specially laid conductors.
Rice. 23. Checking electrical circuits directly
With this method, you can use two probes, the first of which is connected at one end of the EI cable instead of the temporary jumper E2 (item III), and the second one is used to find a grounded circuit at the other end. The probes should be connected to the auxiliary circuit with oppositely polarized probes (positions II and III), so that when they are closed, current flows through the circuit being tested and the indicators change their state.
Fig. 22. Checking electrical circuits using the grounding method
The considered methods are used to test de-energized electrical circuits. However, in some cases, electrical circuits can be checked under voltage using a test lamp, indicator or voltmeter.
Example 25. Direct method of checking electrical circuits. Suppose we want to check the integrity and correctness of electrical circuits in a harness or cable, the beginning and end of which are soldered to plug connectors (Fig. 23). The correct connections are checked by the markings on the connector.
To check the integrity of electrical circuits, one probe probe P is connected on one side of the harness to terminal G of the plug connector, and on the other, with a second probe, a connector terminal that has an electrical connection with terminal G is found. To identify incorrect connections with terminal G, it is necessary to check all other terminals with the second probe connector, as well as its body and harness screen (item II-U), even if the required electrical circuit was found on the first try (item 1). After finding the first chain of 1-G, they also find the second, third, etc.
Example 26. Checking an electrical circuit using the grounding method. Suppose it is necessary to check the correct marking of the E1 cable cores (see Fig. 22). The test begins by installing a temporary jumper E2 at one end of the cable between any residential and auxiliary circuits. Then, touching the probe probe P (item I) to the grounded conductor, check the integrity of the auxiliary circuit. In addition, you should check the integrity and correct installation of jumper E2 by breaking its circuit with the S button and monitoring the change in the readings of probe P.
Next, they begin to search for a grounded conductor at the other end of the cable using the probe probe P (item II). Having found this core, you should open and close the S button or disconnect and reconnect the grounding jumper E2. This is done to ensure that the probe readings are correct and that there are no additional connections, in addition to the E2 jumper, between the found core and the ground and other cable cores. Otherwise, it may turn out that the probe readings are caused by the grounding of one of the cores, independent of the connection of the grounding jumper E2. After checking the first circuit, install jumper E2 on the second circuit and repeat the described steps.
Example 27. Finding a defect using the technological transition “checking electrical circuits.” When checking the circuits of plug connectors XI, X2 and XZ (Fig. 24,a), connected to each other by cables, a defect was discovered in that when connecting the probe P (pos. / and II) to two sockets of the X3 connector, its readings are the same , i.e. the sockets are connected to each other, which according to the diagram should not be. Let's try to find this defect using a heuristic method. 
Rice. 24. Search for a defect in an electrical circuit with a connector:
a - diagram, b, c - checking the connector with a probe
Let's limit the search area for the defect, for which we will find out whether its appearance is associated with interference in the test object caused by connecting the grounding jumper EZ. To do this, it is necessary to break the circuit of the grounding jumper with switch 5 and check whether in this case there is a circuit connecting sockets 5 and 6 of the XZ connector to each other. The test is carried out with probe P, turning it on, as shown in Fig. 24, b.
The readings of the probe with the grounding jumper EZ disconnected indicate the presence of a circuit between sockets 5 and 6. Thus, the defect is not caused by interference with the test object and must be looked for in the object itself.
In the general case, the control object can be a collection of a sufficiently large number of different elements. Where to start your search? Here we will also use the principle of limiting the search area for a defect. The tested object of control consists of a mating part of connector XI, cable E1, connector X2, cable E2 and a mating part of connector XZ, i.e., five elements. With the help of dismountable connections, it can be divided into only two blocks by undocking the connector. The first block will include the mating parts of connectors XI and X2, as well as cable E1, and the second block will contain the remaining elements. Having thus divided the control object into two blocks, we simultaneously divide the area of existence of the defect into two parts. Let's check each block.
Since the defect manifested itself in the formation of a circuit between sockets 5 and 6, we turn on probe P, as shown in Fig. 24, c. In this case, the probe arrow does not deviate, therefore, sockets 5 and 6 do not communicate with each other and there is no defect in the block. Since this block is working, let's move on to checking the other one. Let's connect the probe as shown in Fig. 24, b, and check whether sockets 5 and 6 of the X3 connector communicate with each other when the mating part of the X2 connector is disconnected. Since the probe arrow deviates in this case, there is a circuit between sockets 5 and 6, i.e. the defect is located in this block.
The checks allowed us to identify only a defective unit, but it is impossible to say which of its three constituent elements is faulty. To find the defect, it is necessary to divide the second block into separate elements, that is, disassemble plug connectors X2 and X3 into parts and separate them from cable E2. Since, according to the available information, it is impossible to give preference to any of the elements, then any of them can be separated first, for example, connector X2. Having removed the case and examined the soldering areas, we see that sockets 5 and 6 are connected to each other by a drop of solder, which leads to the formation of a circuit between them, which according to the diagram should not exist.
Example 28. Checking live electrical circuits with a test lamp. Suppose it is necessary to check the circuits in the test object, to which no voltage was supplied after installation (Fig. 25). In this case, first check its power circuits for short circuits. To do this, before applying power, the test lamp H (pos. /) is turned on in series in one of the poles.
Particular attention should be paid to the need for strict adherence to safety rules when working in electrical installations under voltage. Since the test lamp I must be designed for the rated mains voltage, this method can only be used in electrical installations with voltages up to 220 V (it is especially convenient for direct current circuits up to 27 V and periodic current circuits up to 42 V). In installations where accidental connection to circuits with voltages of 380 V and higher is possible, it is necessary to use various voltage indicators or a phase indicator-probe FP-1 (see further Fig. 44, a and the text to it). When using an indicator, before applying voltage to the control object in any other way (for example, using a probe in a de-energized control object), check for the absence of short circuits in its power circuits.
The test lamp must be enclosed in the fittings of a portable lamp (best of all, one that provides for automatic disconnection of voltage from the socket terminals if the lamp bulb is damaged), and all inspection actions must be performed using personal protective equipment - dielectric gloves and safety glasses (mask) . The latter does not apply to testing in circuits with voltages up to 27 V DC or 42 V periodic current.
Rice. 25. Checking electrical circuits with a test lamp
If there are no short circuits in the power circuits of the test object under test, then when voltage is applied to points 0-6, lamp H (pos. /) will burn with incomplete heat and, therefore, it is possible to apply voltage directly to the test object (to points O-4). If the lamp is fully lit, voltage cannot be applied and the cause of the short circuit must be determined.
In the case when, before checking energized electrical circuits, the test object was operating without overloads and short circuits, voltage can be supplied to the power circuit without turning on the test lamp.
A positive property of sequentially connecting a lamp to a power circuit is that the current passing through the power circuit is limited by the resistance of the lamp.
Note that to check live circuits, only incandescent lamps can be used, since the glow of gas-light lamps during a short circuit and in its absence is visually indistinguishable.
Having checked the power circuit, proceed to checking other circuits of the circuit under voltage. In this case, such a property of circuit elements is used as the dependence of the voltage drop across the element on its resistance. On contacts, fuses and similar elements, the voltage drop is practically zero or at least two to three orders of magnitude (at least 100-1000 times) different from the voltage drop on relay coils and contactors, resistors, lamps and other elements that load the circuit .
Let's check the chains of this object control. First, let's check the integrity of the circuit point 0 - fuse F1 - contact KK1.1 - contact KK2.1 - point 2 by connecting one lamp probe H to point 4. If you then touch the other lamp probe to point 1 (position II), then if it is working properly fuse F1, the lamp will light in the same way as when it is connected directly to the network, which indicates the presence of voltage at point 1. By connecting the probe to point 1a, and then to point 2, you can check the serviceability of contacts KK1.1 and KK2:1, as this was done when checking fuse F1. The serviceability of a circuit consisting of series-connected elements can be checked by the presence of voltage at its final element (position Ill) without monitoring the voltage at the intermediate ones.
After this, let's move on to checking the circuit: point 4 - fuse F2 - contact K: 1 with a button S2-button S1-point 3 connected in parallel to it, connecting one probe of the lamp H to the other pole of the source - to point 0. If you now touch the other probe lamp to point 5 (position V), then by the presence of voltage you can judge the serviceability of fuse F2. When the S2 button is pressed and all elements included in the circuit being tested are intact, there should be a voltage at point 3, which, if the contactor coil K is working properly, will cause it to operate.
Thus, by connecting the test lamp I to different points of the circuit, you can check the serviceability of its circuits.
When carrying out electrical installation work, it may be necessary to test the cable, for example, when marking cores and wires, checking the insulation and integrity of the wiring, as well as searching for a broken electrical cable. Let's consider the ways in which testing can be carried out, as well as the equipment necessary for this purpose.
Methods
Testing methods depend on the purpose for which it is performed. To check the integrity of the cable for a break or electrical connection between its wires (short circuit), the continuity test can be done with a tester based on a battery and a light bulb, or you can use a multimeter for this purpose. The latter is preferable.
Despite the fact that the price of a multimeter is higher than a primitive device, we recommend buying it; this device will always be useful in the household.
To check the cable, the multimeter must be turned on in the appropriate mode (diode or buzzer image).
The testing methodology is as follows:
When checking a wire for a break, the tester is connected to its ends as shown in the figure. If the cable is intact, the light will glow (when testing with a multimeter, a characteristic sound signal will be heard).
Explanations for the picture:
- A – electrical cable;
- B – cable cores;
- C – power source (battery);
- D – light bulb.
If the cable has already been laid, then on one side it is necessary to connect the wires together and ring the wires at the other end;
when checking the presence of an electrical connection between the cable cores, the tester probes are connected to different wires. Unlike the previous example, there is no need to twist the wires on the other side. If there is no short circuit between the wires, the light will not light (when testing with a multimeter, no beep will sound).
Testing multi-core cables for the purpose of marking them
When marking multi-core cables, you can use the methods described above, but there are ways to significantly simplify this process.
Method 1: the use of special transformers that have several secondary winding taps. The connection diagram for such a device is shown in the figure.
As can be seen from the figure, the primary winding of such a transformer is connected to the power supply network, one end of the secondary winding is connected to the protective shield of the cable, and the remaining terminals are connected to its conductors. To mark the wires, it is necessary to measure the voltage between the screen and each wire.
Method 2: Using a block of resistors with different values connected to the cable wires on one side, as shown in the figure.
To identify the cable, it is enough to measure the resistance between it and the screen. If you want to make such a device with your own hands, then you should select resistors in increments of at least 1 kOhm to reduce the influence of wire resistance. Also, do not forget that the value of the resistors has a certain error, so first measure them with an ohmmeter.
When checking a multi-core telephone cable, installers often use a dialing headset, for example TMG 1. Actually, these are two telephone handsets, one of which is connected to a 4.5 V battery. Such a simple device allows you not only to check the cable, but also to coordinate your actions during installation and testing.
Insulation check
To test insulation with a megohmmeter or multimeter, the principle of continuity is the same as when searching for an electrical connection between the cable cores.
The testing algorithm is as follows:
- set the maximum range on the device – 2000 kOhm;
- connect the probes to the wires and see what the device display shows. Considering that the wires have a certain capacitance until it is charged, the readings may vary. After a few seconds, the device display can display the following values:
- one, this indicates that the insulation between the wires is normal;
- zero – there is a short circuit between the cores;
- some average readings, this can be caused either by a “leak” in the insulation or by electromagnetic interference. To determine the cause, switch the device to the maximum range of 200 kOhm. If the insulation is faulty, the display will display stable readings; if they change, then we can confidently talk about electromagnetic interference.
Attention! Before checking the insulation of the electrical wiring, it must be de-energized. Second important point– when taking measurements, do not touch the probes with your hands, this can introduce errors.
Video: Wire continuity check - integrity check.
Finding the break point
After a break in the electrical wiring has been discovered, it is necessary to localize the place where it happened. For dialing in this case, you can use a tone generator, for example, the Cable Tracker MS6812R or TGP 42. Such devices allow you to determine the location of the break with centimeter accuracy, as well as determine the route of hidden wiring; in addition, the devices have other useful functions.
Devices of this type include generator sound signal and a sensor attached to the earphone or speaker. When the sensor approaches the place where the UTP cable pairs or electrical wiring wires are broken, the tone of the sound signal changes. When a tone test is performed, the wiring must be de-energized before connecting the sound generator, otherwise the device will be damaged.
Note that with the help of this device you can test both power and low-current cables, for example, check the integrity of twisted pair cables, radio wiring or communication lines. Unfortunately, such devices will not allow you to determine the correct connection; special equipment is used for this purpose - cable testers.
Cable testers
This class of devices allows you to check both the integrity of the cable and the correctness of its connection, which is very important for Internet provider networks. This can be simple devices, checking crossover or complex devices on a PIC controller that have an ADC and a built-in multiplexer.
Multipurpose cable tester Pro’sKit MT-7051N on a microcontroller Naturally, the cost of such devices does not encourage their household use.
Homemade contactless dialing
Below is a diagram of a simple non-contact break detector; it can be assembled within one evening. Given the small number of parts, you don’t have to bother making printed circuit board, but use wall-mounted installation.
List of required radio components:
- variable resistance R1 – 100 kOhm;
- resistor R2 – from 4 to 8 MOhm;
- electrolytic type capacitors: C1 and C3 – 220 µF, C2 – 33 µF;
- ceramic capacitor with a capacity of 0.1 μF;
- D1 – LAG 665 chip (preferably in a DIP package);
- SP – regular earphone from a telephone headset.
The circuit can be powered from a source with a voltage of 2 to 5 volts.
The dipstick (P) is made on the basis of a regular spoke from a bicycle wheel.
Properly assembled contactless cable testing does not require adjustment.
Video: Do-it-yourself cable testing. How to test wires using a light bulb and battery
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