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How to use current measuring clamps

 

When assessing the status of existing electrical installations or performing repair work under voltage, electricians have to measure and compare the values ​​of currents flowing through different circuits. This allows you to analyze the operational scheme, timely eliminate the arising malfunctions.

Quite often, all this must be done without breaking the electrical circuits so as not to disrupt the technological process of power supply to consumers.

There are two ways to measure load currents without interrupting power supply:

1. ordinary ammeters, creating through them at first bypass shunt chains and putting into operation due to the artificial breaking of the current in a previously prepared place. At the end of the measurements, it is required to restore the electrical circuit, to perform in the reverse order all the previous technological operations;

2. Using a tool specifically designed for this purpose - current clamps.

The first measurement method is complex, time-consuming, dangerous, requires highly skilled workers, good preliminary training. Therefore, they try to use it only in extreme cases, and in everyday practice, measurements are made with current clamps.

How to use current measuring clamps

What types of clamp meters exist

Most often, in practice, they occur with a constant (rectified) or alternating sinusoidal current. For both of these species, various mite designs have been created with which it is possible to measure the magnitude and even the direction of power flow without breaking the power supply circuit of consumers in an existing electrical installation.

The photo below shows the measurement of the deviation of the angle of the current vector from the direction of the base voltage in the measuring circuits of protective devices.

Current vector deflection measurements

A method for measuring leakage currents through broken insulation of a car’s electrical equipment using DC clamps and an ammeter is shown in the photograph.

Measurement of the leakage current of the car with clamps and ammeter

The measuring circuit used is assembled in such a way that the clamps themselves show the current flowing through the wire connected to the clamp of the ammeter. Both devices demonstrate the same value, although they operate on different sensitivity ranges.

This example clearly demonstrates the convenience and accuracy of measurement with various instruments. Current clamps for measuring direct current are less common than designs for alternating current, but recently their production has increased significantly.

It should also be borne in mind that manufacturers of measuring equipment have now launched the production of ticks for combined use, which can be used in DC and AC circuits. Such a design, for example, is embodied in the Fluke 376 model and the like.

Fluke Tick Measurement Modes

The current clamps shown in the first three photos have a digital display that immediately displays the primary values ​​of the measured parameters of the electrical circuit. But, in the arsenal of measuring tools for electricians, a large number of devices with arrow pointers and a scale consisting of several subranges still work.

When using such designs, it is necessary to carefully take a count, and sometimes introduce correction factors.

According to the magnitude of the applied voltage, the current clamps are divided into devices operating:

  • up to 1000 volts;

  • or higher than 1 kV.

They differ in the protection class of the insulation used and require different compliance with safety rules.

To properly use any such devices, you need to know the principle of their work and design.


How are current measuring clamps

The device of various models can vary significantly depending on the timing of their manufacture and the complexity of the internal circuit. But the principles of measurement and controls are almost everywhere identical. Therefore, we will take the Fluke 376 model as the basis of the study, which has great capabilities and, accordingly, has an increased number of functions and controls.


The principles of work incorporated in the design

The principle of operation of clamp meters

In the dielectric housing of any device are placed:

  • current transformer with (a) a detachable magnetic drive and a system of levers for its control, (b) a secondary winding;

  • measuring system with information board;

  • controls and switching modes;

  • contact jacks.

To power current clamps, the electric energy of the measured circuit or a set of autonomous voltage sources, for example, two AA batteries, can be used.

Current clamp batteries

The basis of the work is an ordinary current transformer with a detachable magnetic circuit and a secondary winding, the turns of which are crossed by a magnetic flux that induces a secondary current into them. Its value, and in individual designs and direction, is determined by the measuring system, which displays the final result on the display, taking into account the transformation coefficient in primary amperes.

To perform the measurement, it is necessary to place the current conductor inside the magnetic circuit. For this:

  • by pressing the button, the movable elements of the magnetic circuit are bred;

  • wire with current is introduced inside the gap;

  • release the key and track the full contact of the moving contacts.

Sliding magnetic core

When working inside cramped cabinets with a large amount of electrical equipment, it is sometimes difficult to thread the tip of a sliding magnetic core through a current conductor. To simplify this operation, the Fluke 376 has an optional measurement sensor. It is part of the instrument kit and, if necessary, is easily prepared for measurement.

Optional current clamp meter

For safe work under voltage, the pliers are equipped with measuring ends with insulating tips and caps. When installed in the device case, they are recessed in its design. Together with well-insulated lugs, this allows to reduce possible errors in operation, to eliminate the unauthorized creation of accidental short circuits and to receive electrical injuries.

Detachable ends for voltage and resistance measurements

Current Tick Controls

The positions of the rotary mode switch are shown by the Tex inserts in the third picture from above. Their work is complemented by control buttons located on the case.

Current clamp mode control buttons

The ZERO button is used to switch inside the clamp modes set by the central circular switch, and MIN / MAX allows you to specify the measurement limit.

The INRUSH button is for evaluating the inrush current. The convenience of using the device in a darkened workplace is significantly ensured by the built-in backlight, which is entered into the work by pressing the far right button below with the image of lighting.

To fix the current readings on the display, the HOLD button is installed at the side surface of the ticks.

Tick ​​fixation button

In some models of current clamps, some of these functions may be absent or implemented in other ways, but the general principles of measurement are retained for all such devices.



How to measure with current clamps


Preparatory operations

Before each measurement, it is necessary to check the influence of extraneous voltage sources and the interference they create on the accuracy of the device.

Check ticks for no induced voltage

Powerful asynchronous electric motors, power transformers and autotransformers, chokes, welding machines, switching power supplies during operation, they can create strong electromagnetic fields that will induce induced EMF in the magnetic circuit.To take them into account, the ticks are placed in the position of measuring alternating current, tightly closing the sliding elements of the magnetic circuit and controlling the zero reading of the currents on the display.


Methods for measuring currents

The design of the measuring device allows you to determine the current value by simple actions: by setting the mode switches to the appropriate position and by introducing the conductor into the space of the sliding magnetic circuit. The numerical expression of the measured value is automatically displayed.

Measurement of current by ticks through a sliding magnetic circuit

This technology is used on all ticks without exception. But on advanced devices, you can use the IFLex sensor. It facilitates work in tight spaces.

Clamp current measurement via IFlex sensor

Such an operation is always performed for an individual wire because the current passing from it creates a magnetic flux in the magnetic core or IFLex sensor, which is converted by the ticks into a reading.

If two conductors with current are placed inside the magnetic circuit, then the magnetic flux from them will add up and the ticks will show a general result.

Simultaneous measurement of current in phase and neutral wires

Since there are no leaks during normal insulation, the currents in phase and zero will be equal in magnitude and oppositely directed, as shown in the photograph by arrows and signs + I and –I. Each of them will create a magnetic flux, which will add up and destroy the action of each other. As a result, the scoreboard with normal isolation should display a zero result.

If the ticks show a different value in this situation, then this is a serious reason for troubleshooting in the existing wiring.


Useful tips for measuring currents


Optional cable with plug and socket

Clamp measurement through cable adapter

For measuring the current consumption of an electrical appliance, for example, an iron, it may be difficult to phase separation and zero. In a continuous cable, it is impossible to do this without opening it. The issue can be easily solved by connecting the load through an adapter with separate cores.


Increased measurement sensitivity for low currents

The way to improve the accuracy of measuring low currents

For ordinary ticks, it is difficult to determine the values ​​of small currents due to the low sensitivity of the device. The way out of this situation is quite simple: pass the conductor with the measured current through the magnetic clamp of the current clamp several times, as shown in the photo above. In this case, the total magnetic flux increases in proportion to the number of turns and the display also increases.

It remains only to divide the reference value by the number of turns and obtain the exact value even for small currents.

Keep in mind that this technique is only suitable for working with flexible, insulated conductors.


Voltage Measurement Methods

The use of current clamps in a voltmeter mode, in principle, is no different from similar measurements with other devices.

Measurements by current clamps of interphase voltage

The removable ends of the conductors are installed in the nests of the flares, which are previously transferred to the voltage measurement mode by switches. The second ends of the insulated wires are applied to the potential terminals and take the count on the display, as shown in the photo above.


Features of measuring resistance, frequency. temperature

In these modes, the ticks work like an ordinary multimeter and the general measurement rules apply for them. See detailed instructions on how to use the multimeter.


Ways to measure power consumption

Current clamps do not have a direct method for measuring and reading power, but they can perform this operation indirectly. To do this, you will need to determine the methods described above:

  • load current;

  • mains operating voltage.

Then they are multiplied to obtain power. For example, with an electric iron, we measured a current of 9.2 amperes, and the voltage of a household network is 220 volts. Multiply them and get: 9.2x220 = 2024 VA.

We can conclude that the power consumption is two kilowatts.


Checking the absence of extraneous consumers

Using current clamps, you can check the unauthorized connection of consumers to the power cable. To do this, it is enough to install the clamps on the input shield in the load measurement mode and, leaving the usual power on, turn off all the lights and release all sockets from the devices, that is, provide an idle run for the input cable.

If the ticks in this case show a zero value, then there are no unauthorized connections and leakage currents. Otherwise, you must carefully understand the cause of the formation of such a load.


Safety and Accuracy Recommendations

1. Any measuring device is intended for use under certain technical conditions and work with specific loads. You should familiarize yourself with these characteristics in advance and observe them during operation.

For example, for Fluke instruments, the CAT III 600 V or CAT III 300 V markings are used. It indicates that the electrical circuit of the instrument is protected against short-term overvoltages in the measured network up to 600 or 300 volts, respectively.

If the limit of the measured value is unknown, then the maximum value mode is set on the device.

2. Working insulation on the sliding magnetic core and measuring tips prevents the user from creating unauthorized short circuits when working under voltage. It is necessary to monitor its condition. This situation is especially relevant when measuring currents on bare, uninsulated wires.

3. Current clamps belong to measuring instruments. They must undergo periodic metrological verification in the electrical laboratory and have its stamp on the body or a certificate of verification, the validity of which is limited.

4. Since current clamps are used for work under voltage, a prerequisite for their safe operation is the periodic testing of the insulation layer for strength in an electric testing laboratory with the design of the inspection protocol and affixing the appropriate stamp.

Without passing the insulation test and verification, use of pliers in the work, even just purchased from the manufacturer, is prohibited by the rules. Damage may occur if storage or transportation regulations are violated. Presale preparation of the tool in the store is not able to identify defects that have occurred.

5. Before measuring the resistance, it is necessary to make sure that there are no voltage potentials on them. They can not only affect the accuracy of the readings, but also damage, burn sensitive measurement circuits by the formation of dangerous currents.

6. Work with current clamps under voltage refers to the category of life-threatening person. Only trained and trained personnel with an electrical safety group not lower than third are allowed to enter it.

See also at i.electricianexp.com:

  • How sensors and clamp meters work for measuring constant and variable ...
  • Current clamp application examples
  • How to measure the power consumption of home electrical appliances
  • What is an ammeter, types, device and principle of operation
  • How to measure grounding resistance

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    Comments:

    # 1 wrote: | [quote]

     
     

    They did not write how DC ticks work, what kind of sensor there is, and why there is an arrow on ticks