A multimeter (MM), often called a universal controller or tester, allows you to make different types of electrical measurements with a single device. Every electrician, even an amateur, should know how to test wires with a multimeter, conduct DC or AC current before repairing electrical equipment.
The device most often serves as a voltmeter, ammeter and ohmmeter. Used to test electrical resistances or electrical components. They can be used for testing batteries, household wiring, electric motors and power supplies, and other measurement applications:
- constant voltage and current;
- electrical resistance;
- containers;
- frequencies;
- for testing wires and cables of machines;
- parameters of transistors and diodes;
- alternating voltage and current;
- determination of average and peak values;
- resistance measurements with constant voltage;
- resistance measurements with direct current.
Types of measurement testers
A multimeter combines three different types of meters (ammeter, voltmeter and ohmmeter) into one device. Some instruments can perform other types of measurements: for example, they can measure the capacitance of capacitors, test diodes or transistors.
There are three types of multimeters:
- A digital multimeter (DMM) that displays measurements on a digital screen. It is most commonly used for testing. An analog multimeter (AMM) is often used to test hi-fi equipment. It includes a voltage-current converter and a magnetoelectric ammeter. This model does not require a battery to measure current and voltage.
- Fluke multimeters.
The DMM has two probes: positive and negative, marked in black and red, a 9 V power supply (usually a Krona battery), an LCD display, knobs for selecting the required range of modes, an internal circuit consisting of a signal conditioning circuit, an analog-to-digital converter The advantages of a digital MM are its electronic display, high dialing accuracy, and the ability to read both positive and negative values.
The AMM is designed using a moving coil meter and a pointer to indicate the reading on the scale. When current passes through the coil, a magnetic field is induced in the coil, which reacts with the magnetic field of the permanent magnets. The resulting force causes the pointer, attached to drum, deflects on the scale to indicate the current reading. It consists of springs attached to the drum, which provide a force opposite to the movement of the drum to control the rotation of the pointer.
The advantages of AMM are that it is inexpensive, does not require a battery, and can measure fluctuations in readings. You should know exactly how to dial with a multimeter. The two main factors affecting measurement are sensitivity and accuracy. Sensitivity refers to the reverse current of the full scale deviations and is measured in ohms per volt.
Fluke is transient voltage protected. This is a small handheld device used to test wires with a multimeter, measure voltage, current and test diodes. It has several positions to select the desired function. Fluke automatically changes the range to suit most measurements. This means that the magnitude of the signal does not have to be known or determined for an accurate reading, it is directly moved to the appropriate port for the desired measurement. The fuse is protected to prevent damage if it is connected to the wrong port.
Multimeter device
This is a tool that can be successfully used for diagnosing circuits and studying electronic components. It's also great for troubleshooting. The meter has a built-in processor that allows the user to measure a variety of highly functional electrical parameters.
It consists of the following parts:
- display;
- selection knob;
- ports;
- measuring probes (wires or probes);
- current source, "Krona".
The display usually has four digits, as well as the ability to display a negative sign. Some devices have illuminated displays for better viewing in 
low light conditions. The selection knob allows the user to set the meter to detect current (mA), voltage (V) and resistance (ohms).
Two sensors (probes) are connected to two ports on the front panel of the device. COM is common and is almost always connected to ground or negative of the circuit. The COM probe is usually black, but there is no difference between the red probe and the black probe other than ease of measurement. 10A is a special port used when measuring high currents (more than 200 mA). mAVΩ is the port to which the red probe is traditionally connected. This port allows you to measure current (up to 200 mA), voltage (V) and resistance (Ω). The probes have a connector that connects to the device.
Probe types
Most devices turn on in auto-correction mode. There are many different types of test leads (probes) available for this device. Here are some of them:
- IC hooks. These are various lead cables for connecting to power supplies, oscilloscopes, function generators, etc. The cables have red/black pairs.
- Pincer probes connect to existing equipment with edged connectors and allow you to easily test small parts with one hand. The large plastic tweezers are easy to hold and are marked with polarity.
- Needle probes are great for connecting to power supplies and oscilloscopes.
Voltage check
The digital instrument has replaced the analog instrument as a test device because it is easier to read the measurements. They are more compact and have greater accuracy. The device performs all standard functions of an analog AC and DC device.
Checking the functionality of the device:
- The ends of the probes are wrapped together; if working properly, it will show zero or thousandths of an ohm, due to the resistance between the probes.
- When broken, it shows one.
- Some devices have a dialing option, then a buzzer sounds when the probes are shorted.
The device is almost universal. It is capable of working in several modes. Instrument measurement mode:
- switch OFF;
- AC voltage;
- constant voltage DCV;
- AC current ACA;
- DC current DCA.
The device is easy to use. Determining the voltage (U), say, of a battery in a car, which is approximately 12 V at the terminals. The actions will be as follows:
- We connect the probes - red to VΩmA, black to the COM connector. We use the device as a voltmeter, with a parallel circuit for connecting to the network.
- Turn on the device, set the switch to 20 V.
- Connect the probes to the battery, black (COM) to minus - battery output, red probe (V) to positive. The device will display the voltage value. If only 1 is visible on the display, this indicates that a small range has been selected.
DC current measurement
This circuit measures direct current (DC). A number of devices, for example, the DT 830V, are used to measure exclusively DCA current. When measuring current, the device is used as an ammeter with a parallel connection to the object. Procedure for determining electric current:
- Probe connections: black - COM socket, red - VΩmA socket (up to 200 mA) and switch on the DCA icon, 10A connector (200 mA - 10 A) and MMA switch lever for 10A sector. When in doubt, measurements should begin with the highest scale point. Connect the MM to the measuring circuit and turn it on, set the switch to the desired position, break the electrical circuit into which we connect: the red cable (V) to the positive pole of the power source, and the black wire (COM) to the negative. The display shows the current current value.
- You must be extremely careful; if the device is mistakenly connected in parallel in voltmeter mode, not only the fuse and the device itself may fail.
- You cannot measure large currents in a multimeter switch set to 200 mA, otherwise the MM fuse will fail (it will need to be replaced with a 200 mA, 250 V). The 10A multimeter input is generally not protected by any fuse! You need to measure a large current very quickly and you cannot keep the MM turned on for a long period, otherwise a real failure of the device may occur. Many device manufacturers recommend measuring current more than 5A for about 15 seconds.
Resistance testing with a tester
It is used as an ohmmeter for. Measurements can be started from both low and high ranges, unlike current and voltage measurements. The MM is switched on parallel to the measured object. First de-energize the electrical circuit, otherwise failure and breakdown of the measuring device will occur. Procedure:
- De-energize the power circuit.
- Disconnect the indicator from the circuit.
- Connect the cables: black - COM, red VΩmA. Switch - Ω position.
- Connect the multimeter sensors; the required resistance will be displayed on its display.
You should remember the safety rules. When using the MM in ohmmeter mode, be sure to:
Testing of high voltage wires
A multimeter in ohmmeter mode can be used to check for high voltage wire (armor wire) problems if the vehicle has an intermittent high voltage (plug) fault. Before starting this procedure, it is recommended to study the instructions. Measurement procedure:
- Turn on the digital MM, then turn the control dial to the resistance position. Resistance is measured in ohms and is designated on the dial by the capital Greek letter omega.
- Connect the red (positive) MM probe to the positive external field of the ignition coil.
- Touch the black (negative) MM probe to the outer negative post of the device to measure the resistance of the primary coil. If the readings differ from those shown in the vehicle manual, the ignition coil must be replaced.
- Connect the black MM probe to the center negative terminal of the ignition coil. This creates resistance for the secondary coil. Again, if the resistance tested is not what is given in the owner's manual, the ignition coil is not working and the integrity of the system is compromised.
Checking ignition cables
The ignition cable must be subjected to careful visual inspection. If it is porous, has cracked insulation, oxidized contacts or other damage, the wiring must be replaced. If the ignition cable appears normal, its function can be measured using a multimeter to test the wires:
- Set the ohmmeter to 20 kOhm.
- Attach one pin to the end of the cable.
- Read the result on the digital display of the device.
Important to remember! A discrepancy between the instrument readings indicates that the wiring is not working properly. Permissible resistance values:
- Ignition cable copper core: from 1 to 6.5 kOhm.
- Inductive resistor and carbon resistor: The value is determined based on the resistance multiplied by the cable length (plus tolerance).
- Ignition cables have inductive resistance: from 2.2 kOhm to 8 kOhm.
- Ignition cables carbon resistor: from 10 kOhm to 23 kOhm.
Checking the wire for a break with a multimeter
A broken wire can cause the vehicle or part of its equipment to malfunction, which is especially dangerous in a moving vehicle.
Using a multimeter, you can find damaged wires, even if it is hidden inside the insulation. You can check the high-voltage wires with a multimeter using as follows:
The above measurement procedure is general; for a more accurate measurement procedure, you must carefully read and follow the instructions of the multimeter manufacturer.
In modern life, there are often situations when it is necessary to ring a certain circuit or electrical device with a tester. Most often they occur when a socket or key switch stops working, as well as when contact is lost or there is a break in the power circuits of individual devices. If the owner is used to doing everything on his own, he needs to acquire a very practical and easy-to-use device called a multimeter.
With its help, you can check the serviceability of any electrical device, including a regular light bulb, a section of wiring or a conductor included in it. But in order to correctly test a circuit with a multimeter, you should first become familiar with the basic techniques for working with it.
In the following sections of the article, each of the possible options for using a multimeter will be discussed in more detail.
Continuity check (searching for the right conductor)
To check the integrity of electrical wiring or search for one core in a multi-core cable, a digital tester turned on in resistance measurement mode is quite sufficient. When carrying out such an operation, it is necessary to create a closed chain consisting directly of a multimeter (tester), a pair of measuring “ends” and the conductor being tested itself.
In this case, a small electric current is passed through the test area, and the multimeter determines the value of its internal resistance. This is not a dialing test yet, but it is a fairly convenient method.
During such a test, according to the readings of the multimeter display, it will be possible to judge the integrity or break in the section of the circuit or conductor being tested. A reading of zero or close to several ohms means that the wiring is not broken; at the same time, the electric current generated by the device flows freely through it.
It is also possible that during testing it is discovered that the device displays readings in the megohm region, but does not produce a sound signal during the test call. This means that there is an internal break in the wiring section that is not visually detectable.
Essentially, a vertebra is a determination with a multimeter whether there is contact between the wires or not. The multimeter produces a small current, and if the circuit is intact, then the voltage is recorded, as a result, a sound signal is heard - a bell, and zeros are displayed on the multimeter display. The continuity test checks fuses, light bulbs, wires, and the integrity of circuits.
In a similar way, using a multimeter, a short circuit of conductors is detected, which in working condition should not have contact with each other. In a working cable, each individual core should show a small resistance (from fractions to several ohms) when tested.
The resistance value is determined by the total length of the cable product being tested with a multimeter. At the same time, there should be no contact between all components of the multi-core cable and adjacent conductors, which checks continuity.
Wiring check
Testing conductors using a multimeter is functionally provided in most digital devices of this class. To set the dialing mode, just set the switch to the position marked with the “Buzzer” icon and prepare the measuring chain shown in the figure.
If current flows through the piece of wire being tested, the multimeter will produce an audible signal (buzzer). Naturally, to test a section of a circuit several meters long, you will need an additional wire used to expand the measuring circuit.
Another option for testing phase and neutral linear conductors of considerable length involves twisting them at the remote end of the electrical wiring.
In this case, to check the circuit for an open circuit, it is enough to connect the multimeter's test leads to the free contacts of those ends of the electrical line that are located closer to the device.
The last of the proposed options has the following advantages:
- using this method, you can use a multimeter to immediately test both wires of electrical wiring connected in a series chain;
- checking the wire in this way is much easier than the first way, since you can do without an additional segment that allows for extension of the measuring circuit.
Before checking the electrical wiring hidden in the thickness of the walls, you should first carefully read the wiring diagram. In addition, it is necessary to remove the operating voltage from it by turning off the circuit breaker corresponding to this line.
Using improvised means
Testing wires with a multimeter is not the only possible option for testing them for continuity or breakage. You can verify the serviceability of any linear conductor without the help of this universal device.
To carry out such a check you will need:
- a regular battery (preferably a 4.5-volt square one);
- a 3.5 Volt light bulb, with which the linear section of the wire being tested is checked (monitored);
- a pair of connecting wires and a gripping type connector (the so-called “crocodile”).
After preparing all the necessary elements, a simple measuring chain is assembled on their basis, consisting of a test light, a battery and the conductor being tested. If the circuit is correctly assembled and if the tested area is in good condition, the control light will light up. The absence of a glow even though all circuit elements are working properly indicates a break in the conductor itself.
When testing in this way, the same principle is used as when checking with a multimeter turned on in the dialing mode.
Features of checking wires included in various devices
First, let's look at the features of work in conditions where the on-board wiring of a modern car is checked using a multimeter.
Automotive wiring
The specificity of this situation is that the wiring in the case under consideration consists of one linear conductor with a supply voltage of 12 Volts. In this case, the metal body of the car is used as the second (common or “ground”) conductor, where, as a rule, there is nothing to break.
To prepare the on-board network for inspection, you first need to disconnect the positive terminal from the battery, after which you can safely begin work. Testing of on-board wiring is organized according to the previously described linear circuit testing scheme.
When checking the “ground” of a car, the main attention is paid to the quality of contact of the supply terminals with the body.
Electric heating element
Based on the indicator readings on the multimeter, it is possible to make a continuity test on an element such as a water heating element. During the test, the control probes of the device touch the two contact plates of the heater and evaluate its internal resistance using the indicator.
If the display shows about a few ohms, then without a doubt the element is working. With large values on the screen corresponding to a break in the line being tested, you can immediately say that the heating element is damaged and must be replaced.
In addition to the heating element itself, when checking boilers and similar devices, it is very important to ring the supply cable for unwanted contact with the device body. For this purpose, one of the multimeter probes is connected in turn to the input contacts; in this case, the second end is constantly held on the heater body.
If the digital multimeter shows some resistance during measurement, this means that the protective sheath of the supply cable is damaged. To prevent electric shock to the user, it should be replaced with a new one.
Other household appliances and parts
Using a multimeter, you can test the power circuit of any lighting device by testing the wiring and auxiliary elements (switches, in particular) for a short circuit or open circuit. To do this, first of all, you should ring two linear chains ending directly at the contacts of the light bulb.
Additional Information! Before testing the lighting device, first of all, make sure that the light bulb itself is working properly by replacing it in a known-good device.
When testing linear chains, be sure to check the serviceability of the switch located in one of them, as well as the reliability of connecting the conductors to its contacts.
We also note that using this method it will be possible to ring the windings of a linear transformer or electric motor and verify their integrity or the presence of a break (short circuit).
In conclusion, let us remind you once again that using a multimeter you can check not only individual wires or wiring hidden in the thickness of walls, but also any other electrical devices and parts.
If you need to find the cause of a breakdown in equipment or electrical wiring, you first need to test the conductors using a special device called a multimeter. This is a tester that will help determine wire integrity and resistance. And also, you can understand whether there is a short circuit in the circuit. Using this device, you can find out whether an incandescent light bulb, fuse, transformer or heating element is working.
If you want to determine the integrity of electrical wiring in an apartment, then you need to know the features of using a multimeter. First, you need to know that for such purposes you don’t need an expensive device; you can get by with a simple Chinese tester that does not have special capabilities.
However, the most practical option is to use a device with dialing capabilities. To turn on the mode we need, turn the tester knob to the icon that shows a diode or a picture of a wave. In this mode, if the conductor is working properly, a squeak will be heard.
The sound signal will not always appear. If the wire is faulty, the number one will appear on the screen, which indicates that the resistance is higher than the limit in the measurement. If the circuit is working properly, the conductor resistance will appear on the display. In the best case, this indicator should be around zero if the conductor is short.
The continuity of wires and cables is as follows:
- The next step is to check the serviceability of the device. To do this, you need to connect the multimeter probes to each other. If you hear a squeak, then everything is in order and you can start testing the cables.
- After this, you should take a conductor with well-exposed wires, without dirt and oxidized metal, and touch the ends of the cable with the probes.
- If the circuit is working properly, you will hear a characteristic sound, and the display will show the resistance value or just zero. If the number one appears on the screen, but there is no squeak, this means that the circuit is faulty.
When working with electricity, certain rules must be followed:
- The best option would be to use so-called crocodiles, which will make the work easier. They will make contact more reliable and will not occupy your hands during measurement.
- Before checking the circuit, it must be disconnected from the network. It is important to remove even ordinary batteries from the circuit, and short-circuit the capacitors, if any, thereby discharging them. If you neglect this rule, the tester will break.
- When checking a long cable, do not touch bare areas with your hands, as the results may be distorted.
If you want to check the integrity of the wire with a large number of cores, then they need to be cleared of insulation and separated among themselves. Next you need to make sure that the wires are not shorted. To make it more convenient, you can fix one core with a crocodile, and check all the others with a probe with all the options.
In this version, a squeak will mean that the wires are shorted together. When testing cables designed to operate with high currents, this point is very important.
The next step is to check if there is a violation in the conductor. For convenience, you can connect all the wires on one side. If there is no sound on any conductor, it means that it is damaged.
How to check the integrity of wiring in an apartment
As an example, we will take an average new apartment, in which the wiring is done with high quality, with all standards. This means that all cables for the light and for powering the sockets were routed separately. Each cable is separately connected to the panel through its own machine.
If the light in the room goes out, you need to immediately check whether the lamp is working properly. Before doing this, you need to turn off the power to the room or the entire apartment. To check the serviceability of an incandescent light bulb, we will need a tester.
First of all, you need to determine whether the machines in the panel have worked. If not, then the fault lies in the light bulb, socket or switch. In this case, the wiring is unlikely to be damaged. If the circuit breaker turns off the power, then you need to ring the entire circuit, excluding the switch in the room.
Sometimes it happens that although all the light bulbs in the room are intact, the light in one of the rooms suddenly goes out, or some seemingly serviceable household electrical appliance stops working, or one of the switches starts to malfunction, etc. This is where we have to resort to the so-called “dialing” procedure, that is, it is necessary to somehow check the integrity of some conductors.
The conductor could be damaged during repair work, the connection point could burn out due to overload under poor-quality installation conditions, and you never know for any reason the wire could break... Often in such cases we are faced with a situation where inside the junction box on the wall we find mixed up connections. marked wires and strands, tightly wrapped with electrical tape.
What should you do if you need to check all the wires, identify a break, eliminate the malfunction, but the wires are mixed up? Afterwards, of course, we will mark the wires so that there is no confusion in the future. There is an answer: you need to be able to determine which wire goes where. So, let's focus directly on dialing in the most ordinary non-professional circumstances.
Some electricians use tricks like batteries and a light bulb to figure out which wire goes where. If there are only two wires being tested, and they go to a single outlet, then there is no need for wisdom. What if there are dozens of sockets and wires? This is where smart dialing is needed, which will help you understand which wire is connected to which switch or which socket.
The procedure is performed with a preliminary shutdown of the power supply to all wiring in the room. The circuit of a homemade wiring integrity tester consists of series-connected: a 12-volt light bulb, a battery (a small 12-volt battery) and connecting wires with alligator clips at the ends.
The operating principle of the improvised tester is shown in the figure. Variations are possible regarding the battery and light bulb ratings; here the craftsmen invent whatever they want. Everything is done very simply: the first crocodile is connected to one end of the wire being called, the other to its other end.
The circuit is as follows: current source, connecting wire with a crocodile, wire being tested, connecting wire with a crocodile, light bulb, current source. If the light comes on, the circuit is intact, the wire is intact. Wires whose integrity has been confirmed by continuity are marked.
Multimeter
Less cunning and more technologically advanced. The device is switched to resistance measurement mode at the smallest range on the scale, after which the resistance value of the suspected conductor is checked with probes.
First, the probes are connected to each other, and the device should show zero resistance - there is contact; when the probes are separated, the resistance is infinite - one without zeros on the left of the display.
The same is true when checking a conductor: if the resistance goes off scale into the megaohm region (one without zeros), then there is a break in this conductor. If the resistance tends to zero, or at least to a value adequate to the design of the circuit being tested, then the conductor is intact. It is convenient when the multimeter has a sound indication (diode testing mode).
Checking stranded wires, cables and various windings
If you are dealing with a multi-core wire or cable, and you need to determine which conductor is damaged, then on one side of the wire, connect all its wires at once to one of the multimeter probes, and on the other side, check the resistance on each one in turn. Where the resistance rushes to infinity (or turns out to be much greater than the rest), there is a break (or damage to the core).
If you are checking a long section of wiring, then in order to avoid the use of extension wires, again it is enough to short-circuit two wires on one side in the section being tested. This way, on the other hand, you will ring two conductors at once (for example, if you are checking a two-wire wire).
If the resistance goes to infinity or is much greater than normal, it means there is damage in one of the wires. Usually in this case it is necessary to replace the entire two-core conductor. The windings of transformers and motors, as well as heating elements and so on, ring in a similar way - where the resistance is off scale (or much greater than that of similar circuits located nearby) - there is a break or damage.