Current clamps are special devices that are widely used for measurements without the need for a circuit break or any additional electrical contact with it.
Instead, this device measures the strength of the resulting magnetic field, which generates the current.
For correct operation, it is recommended to select the appropriate type of device, check them properly (we will talk about the options later), and also roughly understand the principle of their design and operation. Let's consider the main nuances.
How to use a current clamp?
These devices are very easy to use.
The design of current clamps allows measurements to be taken on an existing electrical installation without any additional installation work and without breaking the power supply circuit. This is their huge advantage. To measure, you need to set the switch to the desired position, wrap the pliers around the wire and record the current readings. The main difficulty in such measurements is to isolate a separate single conductor. If you grab the entire wire (phase and neutral conductors) with pliers, you will get the sum of the currents flowing through both wires. Ideally, zero should be displayed here, since the currents flowing through the phase and neutral conductors are equal in magnitude, but opposite in direction. As shown in the photo below, you will not learn anything and you cannot measure current this way. Although if in this position the clamps show any current value other than zero, this will mean that there is a leak in this circuit equal to the obtained value.
Therefore, it is necessary to find a place where these conductors are separated, and where there is an opportunity to crawl with pincers. For example, in a distribution panel at the point where the phase is connected to the circuit breaker. Unfortunately, this cannot be done everywhere. This is their slight disadvantage, but the ability to measure without breaking the circuit completely overcomes it, at least in my work.
I work in communication rooms where it is strictly forbidden to de-energize communication equipment, so current clamps are the only device that can measure current and calculate the consumed load.
How they work and what types there are, read the article: What are current clamps and why are they needed?
The instructions below are based on the Fluke 302+ model. These are high quality and good clamp meters, but they can only measure AC current. Direct current is measured by other models of clamps in the same way as alternating current, only it is necessary to switch them to the direct current measurement mode.
Before any measurements, make sure that your clamp meter model can be used for this purpose. They indicate the maximum current value that can be measured with them. In my case it is alternating current up to 400A. Although you will not find such high currents at home and therefore any model will be suitable at home.
The safety category is also indicated on the measuring instruments themselves. In my case, the Fluke 302+ model is marked:
- CAT III 600 V - this means that the device is protected from short-term voltage surges within the equipment when used as part of stationary systems with voltages up to 600 V, such as distribution panels, feeders and branches, as well as lighting systems in large buildings.
- CAT IV 300 V - this means that the device is protected from short-term power surges from primary power supply equipment with voltages up to 300V, such as an electric meter, overhead or underground utility system installation.
Instructions on how to use clamp meters
- We find a place where you can freely grab a single conductor with pliers.
- We move the knob for switching measurement modes to the desired position. On AC power, point to A~ or AAC. In a DC network, point to the A- or ADC indicator. These designations are additionally duplicated on the display. Let me remind you that my clamps do not support the DC current measurement function and therefore do not have this designation on them.
- Press the button to open the ticks.
- We grasp the desired conductor and install the pliers perpendicular to the plane of the wire.
- Release the pliers release button. This closes the magnetic circuit and the current is measured.
- We record the resulting current value on the display. If it is hard to see, you can record the measurement results by pressing the “Hold” button. Then you can remove the clamps and see the measured current value. It will remain on the screen until you press the “Hold” button again.
Above I described the main functions of current clamps, i.e. current measurement without breaking the circuit. I think everything is clear.
To ensure the versatility of this device, almost all manufacturers add additional functions to its design. This is the ability to measure other parameters such as voltage, resistance, etc. I will talk about this in the next article: “Additional functions of current clamp meters.”
Today we miss smiles so much:
Usage example
Let's give an example of how to use current clamps when measuring load on a 220 V network, for example in an apartment. In this case, the switch must be set to position AC 200. Next, you need to grasp the insulated conductor with a current clamp and take readings. After this, the resulting current value must be multiplied by the network voltage of 220 V. For example, if the device shows 5 A, then the power consumption in the network will be P = U * I = 5 * 220 = 1100 W or 1.1 kW. The obtained value can be used to check the operation of electricity meters.
Finally, we suggest watching a video that clearly shows how to use the DT-266 and Fluke 302+ current clamps, which are quite popular today:
DT-266Fluke 302+
That's all the instructions on how to use current clamps yourself. As you can see, there is nothing complicated. The main thing is to follow safety measures and take measurements carefully. We hope that our tips and visual video instructions clearly explained the procedure to you!
It will be interesting to read:
- How to use a multimeter - instructions for dummies
- How to check if your electricity meter is working correctly
- List of electrician's tools
Correct use of the tool
DT-266
Fluke 302+
Material taken from the site:
https://samelectrik.ru/
Varieties
Several instrument classifications are due to the abundance of parameters for comparison. Since current clamps are used to work in high-power circuits with high voltage, the main division is based on safety requirements.
The division is as follows:
One-handed electrical clamps, designed for work in circuits with operating voltages up to 1000 V. The tool is equipped with a key designed to move apart parts of the magnetic circuit of the current transformer. The device is designed to be operated with one hand and is lightweight and small in size. The device's protection class corresponds to operating voltages up to 1000 V;
Two-handed electrical clamps. This tool provides operation in AC and DC voltage circuits ranging from 2000 V to 10 kV. It has large dimensions due to powerful insulation and is designed to be used with two hands, since the magnetic circuit control handles are long.
Both varieties may have a different display system for the measured parameter:
- Analog (arrow) measuring clamps. The oldest variety, which has not lost its relevance today, thanks to a number of advantages: low inertia of the pointer indicator, which allows you to control and measure short bursts of current, the absence of additional power for the internal circuit. There are also disadvantages, and they are significant: sensitivity to shaking and shock, the need to correlate the readings of the dial indicator and the scale factor of the measurement limit switch;
- Digital electrical clamp meters. The main advantage is that the indicator displays the real value of the measured parameter, relieving the user of the need to convert values. The measurement limit switch only adjusts the indicator readings for greater ease of reading. The biggest disadvantage of digital indicators is their dependence on the power source, since they contain a complex electronic circuit on a digital microcontroller inside. The delay in the settling time does not allow the parameters of short pulses to be measured. Inexpensive models are characterized by poor protection from electromagnetic fields, which leads to measurement errors.
Work in electrical circuits is not limited to just measuring current; other electrical parameters of the network are also important, which is why a whole class of combined tools based on current clamps has emerged:
Phase meters. Serve to determine the phasing of wires in multiphase circuits; Wattmeters. Instruments that measure power consumption; Voltmeters. Instruments for measuring voltage values on circuit elements; Megaohmmeters
Devices for monitoring insulation resistance, which is especially important in high voltage circuits.
The presence of a combined instrument does not reduce its reliability, since only the display device remains unified, and additional input terminals and circuit elements are used to measure additional parameters. On the other hand, a clamp multimeter significantly improves ease of use and eliminates the need to carry a set of various measuring instruments.
Operating principle
What are clamp meters used for?
They are a type of electrical tester with wide jaws that can pinch the electrical conductor. They were originally developed as a general-purpose instrument for measuring alternating current. However, as their design improved, clamps included inputs for receiving test leads and other sensors that support a wide range of measured values. Indispensable as a testing tool, meter clamps make it easier to work in confined spaces and allow you to work on live conductors without interrupting the circuit. Being a high-precision meter, pliers cannot be made in non-specialized workshops or with your own hands.
The measuring clamps implement the principle of magnetic induction, which allows you to determine the current value in a non-contact manner. Electric current flowing through a conductor induces a magnetic field around it. Since the polarity often changes, dynamic oscillations of the magnetic field occur, which are proportional to the current strength.
All sizes of current clamps operate using the Hall effect - the presence of transverse voltage that occurs when a conductor is placed in a magnetic field. Inside the housing there is a transformer that determines the intensity of magnetic oscillations, converting their value into an indication of alternating or direct current. Therefore, even if the resulting potential difference is small, the sensor will detect a magnetic field. This voltage, which is proportional to the current, is then amplified and measured (see Figure 1). Very powerful currents are measured in this way.
Figure 1. AC current measurement circuit
How to measure current using a transformer
When a conductor is passed through the terminals of the device, current passes through these terminals, acting as the iron core of a power transformer. Next, the current flows into the secondary winding, which is connected through the meter input shunt. Due to the ratio of the number of secondary windings to the number of primary windings wound around the core, the current entering the input is much less. Typically, the primary winding consists of one conductor, around which the jaws are clamped. If the secondary winding has, for example, 1000 turns, then the current in the secondary winding will be 1000 times less than that flowing through the primary winding. Thus, 1 ampere in the conductor being measured will produce only 1 milliampere at the instrument input. By increasing the number of turns in the secondary winding, powerful currents can be easily measured.
How to measure direct current, because it flows through conductors with a fixed polarity? Here the magnetic field around the conductor does not change, and it is impossible to record the corresponding readings in the usual way. Therefore, the clamps around such a conductor are closed with some gap (see Figure 2).
Technology of use
The instructions for current clamp meters are not very complicated. The main thing is to study the possible measurement modes and use the device in accordance with it. If it is necessary to make measurements on a single wire, then the appropriate mode is selected. To do this, the switch handle is moved to the desired position.
After fixing the measurement range, you should attach the pliers to the wire, grasping the conductor, and position the device perpendicular to the direction of the core. After this, you need to determine the results on the screen.
If the number “1” is recorded on the display, this indicates an overload, which means you need to move the switch to a higher range, having first disconnected the device from the wire.
Often it is not possible to isolate a single wire, for example, when measuring a cable coming from an outlet. When work is carried out, the indication “0” will appear. This indicates that the currents in phase and zero are equal in magnitude, although they will be different in the direction of the current.
When taking measurements on a power cable, several wires are inserted into the pliers. In this case, you need to select the appropriate mode.
If you want to learn how to properly use a clamp to measure voltage, you need to connect the red probe wire to the “VΩ” connector and the black wire to the “COM” connector. Using the switch, you will need to select the mode and set the measurement limit. After connecting the probes to the source, an indication of the polarity and voltage value will appear.
Similarly, resistance can be measured by connecting probes. But the switch should be moved to the “Ω” position. If the circuit has a resistance greater than 50 ohms, a warning signal will sound.
Safety precautions when working
Working with clamp meters is inherently safe, but it is necessary to take into account some features of the measurement procedure. When using this device, do not exceed the selected measuring range. Electrical clamp meters prohibit changing the measurement range during the measurement process. And, of course, it is forbidden to touch non-insulated parts of the device during operation. Always, before using the device, you need to study the information from the section on how to correctly take measurements with current clamps. In this case, the device can serve for a very long time.
The operational documentation contains information on how to configure the device, indicates the period, frequency and parameters when it is necessary to perform calibration. When used even as a voltmeter, the device requires verification. Verification is carried out in a specialized laboratory.
ElektroMaster.org DIY repair and maintenance of household electrical appliancesTips, guides..
Yandex.Direct
Ammeter is a device for measuring current in amperes. The scale of ammeters is calibrated in microamperes, milliamperes, amperes or kiloamperes in accordance with the measurement limits of the device.
In an electrical circuit, the ammeter is connected in series with the section of the electrical circuit in which the current is measured; to increase the measurement limit - with a shunt or through a transformer.
(An example of an ammeter with a transformer is a "current clamp"
Ammeter
Current clamp - Ammeter for non-contact measurement of large currents, allows you to measure current strength in a non-contact way with high accuracy, without interrupting the power supply to consumers.
When measuring current, the clamp probes, in which ferrite cores are mounted, seem to wrap around the conductor, remaining completely isolated from open sections of the wires.
Important
Due to the formation of an oscillatory circuit by ferrites when current flows through the conductor, magnetic induction occurs, the value of which is directly proportional to the current flowing through the conductor.
This value is recorded by the current sensors of the current clamps and is converted into a current value, which is either displayed on the display of the current clamps (if it is designed) or outputs the value to an external multimeter through remote probes. Depending on the modification, current clamps can measure the strength of both direct current and alternating current.
Current clamps
general characteristics
The most common ammeters are those in which the moving part of the device with the pointer rotates through an angle proportional to the magnitude of the current being measured.
Ammeters are magnetoelectric, electromagnetic, electrodynamic, thermal, induction, detector, thermoelectric and photoelectric.
Magnetoelectric ammeters measure direct current; induction and detector - alternating current; ammeters of other systems measure the strength of any current. The most accurate and sensitive are magnetoelectric and electrodynamic ammeters. Operating principle
The principle of operation of a magnetoelectric device is based on the creation of torque due to the interaction between the field of a permanent magnet and the current that passes through the winding of the frame. An arrow is connected to the frame, which moves along the scale. The angle of rotation of the arrow is proportional to the current strength.
Electrodynamic ammeters consist of fixed and moving coils connected in parallel or in series. The interaction between the currents that pass through the coils causes deflections of the moving coil and the arrow connected to it. In an electrical circuit, the ammeter is connected in series with the load, and at high voltages or high currents - through a transformer.
The material partially uses information from wikipedia.org
Example of calculating total power for an electric motor
The power of electric motors can be useful or mechanical on the shaft and electrical. They differ by the coefficient of performance (efficiency), this information is usually indicated on the nameplate of the electric motor.
From here we take the data to calculate the connection in a triangle to Ulinear 380 Volts:
Then you can find the active electrical power using the formula:
P=Pon the shaft/n=160000/0.94=170213 W
Now we can find S:
It is this that needs to be found and taken into account when selecting a cable or transformer for an electric motor. This completes the calculations.
How to use current clamps »
The main task of electrical clamps is to measure current without breaking the conductor; modern devices have the functions of measuring voltage, capacitance, temperature, power, etc. The measuring principle is based on a current transformer or Hall effect.
Current clamps, operating on the principle of a current transformer, measure only alternating current, because The transformer does not pass direct current through itself. The primary winding is a wire wrapped around the current clamps, and the secondary winding is inside the current clamps with a current sensor.
If you wrap several turns of one conductor, the current on the secondary winding will increase by the same amount. This is convenient for measuring small alternating currents, in which case you need to divide the resulting current value by the number of turns.
Important
Externally, current clamps operating on a current transformer are distinguished by the absence of notches on the jaws and the absence of a direct current range.
Hall effect current clamps measure both direct and alternating current. The principle of operation of the Hall effect is based on measuring the voltage on the edges of a semiconductor wafer through which a direct current flows, placed in a magnetic field perpendicular to it. A magnetic field is formed around a conductor that is clasped by a current clamp.
A change in current in a conductor causes a change in the magnetic field around the conductor, which causes a change in voltage across the Hall sensor element. The voltage at the sensing element is converted and displayed as a current value
For hall effect current clamps, it is important to place the conductor perpendicular to the current clamp jaws
Current measurement
To work on our APPA 133 device, we will select the alternating current mode A~ and wrap around one wire. The selection of the measuring range in APPA 133 is automatic; in other devices it may be necessary to select a range. If the conductor is not placed perpendicularly or along the marks, then the reading error increases to 3%.
To measure inrush AC current, you must select the “inrush current” mode, for example, in the case of measuring the inrush current of an electric motor. To measure the max min current, select the appropriate mode. When the stove is on, the maximum current is 8.47 A.
If you grasp two wires at once, the current clamp will show zero, because the sum of the currents of two conductors with different polarities is zero.
If the instrument reading is not zero, then there is a leakage current or the value is within the instrument error. When measuring several wires at the same time, the current value will be the sum of the currents of all wires.
A current leak may appear, for example, if the water from the tap is electrifying, you need to check the leakage current of the electric boiler.
Voltage measurement
To measure direct and alternating voltage, set the switch to V. Our device has automatic range selection and also allows you to measure frequency. It is necessary to switch between modes with the wires disconnected. APPA 133 has high voltage protection over 1000 V.
We see a voltage of 221.1 V, a frequency of 49.97 Hz.
When the stove is turned on, we see that the voltage has dropped to 211.1 V, the frequency has not changed. This happened due to the fact that the cross-section of the wires is not enough for the power of the stove, which causes overload and heating of the wires. It is necessary to change the wires to a thicker section.
Power consumption measurement
Apparent power (V*A) is equal to the square root of the sum of the squares of active and reactive power. Reactive power (Var) is equal to the product of voltage and current multiplied by the sine of the phase angle between them. If there are no consumers with reactive power (motors, transformers), then the total load power will be equal to the active one.
Active power is calculated in the device using the formula voltage times current. If the device does not allow you to measure power, then multiply the resulting current by 220 V and get the load power. To measure active power using APPA 133, move the W~ switch. It is necessary to switch between modes with the wires disconnected.
We insert the probes into the socket and wrap around the conductor.
The active power consumption of the computer is 28 W, and with the stove on, the power consumption increased to 1728 W (~=211.1 V * 8.47 A). In APPA 133 you can also measure the power factor, a negative value indicates the capacitive nature of the load (current leads the voltage), a positive value indicates the inductive nature of the load (current lags behind the voltage).
You can select current clamps in the catalog.
We calculate the power of a three-phase network
For the calculation, we will take a certain production workshop in which thirty electric motors
. A four-wire line enters the workshop, remember that these are 3 phases: A, B, C, and neutral (zero). Rated voltage 380/220 volts. The total power of all engines is Ru1 - 48 kW, we also have lighting lamps in the workshop, the total power of which is Ru2 - 2 kW.
Read also: What are nerves in teeth for?
- Ru - the installed total power of a group of consumers, equal in value to the sum of their declared capacities, measured in kW.
- Kc is the demand coefficient at the highest load mode. The demand factor takes into account the largest possible number of activations of the group's receivers. For electric motors, the demand factor must take into account their load.
The demand coefficient for the lighting (lighting) load, that is, lighting, is Ks2-0.9, and for the power load, that is, electric motors, Ks1 = 0.35. Average power factor for all consumers cos(φ) = 0.75. It is necessary to find the calculated line current
.
Popular models
The difference in price may be due to both the use of a well-known brand and the materials used to manufacture the device. Let's look at the most popular current clamps on the Russian market.
Mastech 266
Mastech model M266
There are three modifications of these current clamps: M266, M266C and M266F. The additional letters C and F in the model names indicate the ability to measure temperature and frequency. The models do not differ in shape, color and other parameters.
Country of origin: Hong Kong. All current clamps of the M266 series measure:
- Alternating current – up to 1000 Amperes;
- AC and DC voltage – up to 1000 Volts;
- Resistance – up to 2 Mohm;
- Diode check
All models are supplied with high-quality electrical probes with good contact in the device. Convenient “Hold” button for recording readings on the screen under your thumb. Model cost:
M266 – $30;
M266C (with thermometer) – $31.50;
M266F (with frequency measurement) – $31.50.
Resanta DT 266
Resanta pliers DT 266
Chinese current clamps are of low quality and have a number of functional disadvantages:
- The probes quickly break at the junction of the cable and the plug.
- Poor dust protection of the device leads to contamination from inside the screen. If the device is used in dusty conditions, the screen becomes unreadable over time.
- Over time, play when opening the pliers leads to inaccurate connection of the jaws, and this leads to inaccuracies in measurements.
- There is no screen backlight. It is impossible to work in a room with poor lighting.
- The error of the device does not correspond to the declared one and is about 5%, which is unacceptable for such a multimeter.
- The response speed is very low compared to analogues. Voltage measurement lasts 2-5 seconds, current measurement lasts 6-8 seconds.
- Small symbols on the front panel of the device. It's difficult to make out what exactly is written. The paint with which the markings are applied is easily erased and after six months of work you can only switch from memory or by looking at the instructions
In general, the device is intended for use only in high voltage environments where high measurement accuracy is not necessary:
- Voltage DC/AC – 1000/750 volts;
- Connection testing;
- Resistance – up to 2Mohm
The undeniable advantage of this model is the price of $10.50, but considering that the service life of such a device will not exceed one year of active use, and during this time you will have to buy additional probes for it a couple of times, you will not get pleasure from using it.
Fluke 376
Fluke 376 Clamp Clamp with iFlex Sensor
One of the best devices in this segment. American quality is strikingly different from everything else on the market. High measurement accuracy (from 0.1%), protection from dust and adaptability to work in extreme conditions make these pliers the most popular among professional electricians.
A special feature of the device is a special iFlex sensor - which comes as standard. With its help, you can check the current in those cables, due to their cross-section or location, they cannot be grabbed with pliers. The sensor is connected to the connector from below.
Using iFlex for Measurements
The device is equipped with high-quality electrical probes that connect to the same connector. The display is white, the readings are easy to read, there is a backlight and a Hold button that “freezes” the readings at the right moment. Measurements:
- AC/DC – 1000 amps;
- Current using iFlex sensor - 2500 amperes;
- Voltage (AC/DC) – 1000 volts;
- Frequency 5 – 500 hertz;
The pliers operate on two AA batteries. Their only drawback is the high cost of $244.30, which, of course, is incomparable with Chinese crafts, but the professional quality of the device is worth the money.
Device and principle of operation
Current clamps include several components.
- A magnetic circuit that is opened and retracted using a spring mechanism with levers (this mechanism resembles tongs).
- The housing contains a measuring device, which includes a display (or a pointer electrical measuring head), a measurement range switching board with a multi-position switch. Digital devices can have either an electronic board with the functionality of a full-fledged multimeter or an ammeter. In more “advanced” devices, instead of a switching unit, there is a digital selector that automatically selects the desired measurement limit. The universal device with current clamps has separate connectors for selecting voltmeter or ohmmeter mode. The latter mode is used for measurements on disconnected electrical installations and circuits.
- The analog device is also equipped with additional calibration variable resistors - they help to more accurately establish the measurement zero if it is lost. This is necessary for extremely accurate measurements.
- If the current is measured in protected and difficult-to-access circuit points, the current clamp device includes a meter with a highly sensitive and flexible probe.
The operating principle of current clamps is as follows. It is based on the effect of electromagnetic induction. The wire on which the operating (load) current is measured is inserted into the gap of the magnetic circuit. There is a secondary winding on that one. The primary current on the wire being measured creates an alternating magnetic field around itself, which is captured by the magnetic circuit. It, in the form of a magnetic flux, reaches the secondary winding and induces an induced emf in it. The magnitude of the current in the wire and the secondary current generated in the coil are strictly correlated, and the primary current is easy to estimate.
Since an unbroken ring of the magnetic circuit would require the insertion of a section of wire folded in half, on which the current is measured, and the measurements would be very inaccurate, the magnetic circuit is made in the form of round pliers - a break is formed in it when the handles are pressed, and only when this wire needs to be put on tool.
For example, transformer steel can be used as a magnetic core - if we are talking about an industrial frequency of 50-60 hertz. The difference between clamps and a current transformer is that the latter has an unbroken ring or a rectangular contour.
But a special breakthrough in this area was achieved thanks to the discovery and introduction into use of electricians and power engineers of the Hall sensor. It allows you to measure not only alternating current, but also direct current - using the same current clamp method.
How to use a clamp meter
The value of the basic electrical parameters can be obtained using certain instruments. One of these devices is special pliers that allow you to take readings without breaking the chain.
These “smart” devices are very often used, as they allow you to obtain several types of parameters. You can purchase measuring clamps in almost any specialized store, where you can also immediately get advice on their use.
Main characteristics
Clamp meters are a special mechanism that allows you to determine the strength of alternating current without breaking the main circuit.
This product consists of several main components:
- magnetic circuits that can open and close in a certain way;
- range switch;
- display;
- output connectors for probes;
- buttons for fixing current measurements.
The clamp meter can also be used as a regular multimeter, making its design versatile. Each type of device must indicate the safety category and the maximum measured current.
There are several types of ticks, which allows them to be used in certain networks.
What is rated power?
This definition refers to an established indicator that allows you to connect a certain number of pieces of equipment at the same time. If you exceed their permissible number, the automatic protective system may fail. The calculation of installed power is carried out by summing this indicator, which characterizes each connected device in the system.
Important! The interfloor space of a residential building is equipped with an electrical panel and an input device, from which cables are laid to each apartment. In the case when the system is located in a residential area, a cable with the required cross-section is laid in it
To protect the distribution lines, an automatic machine, a counting device and a shield are installed to evenly distribute the loads on each line.
Electrical panel
