A clamp meter is an instrument for measuring electric current in a conductor. It has a clamp that can be used to make contact with the conductor, and it has an ammeter to show the current flowing through the conductor. The clamp meter must be set up correctly, and then it can be used to measure the current in any conductor.
If you don’t know how to use the clamp meter, feel free to read this article. Here you will find instructions on how to use it.
Principle of Operation
The clamp meter is based on the principle of a simple current transformer. In this case, the primary winding is the bus or cable with the current to be measured, and the role of the secondary winding is played by the clamp, inside of which there is a second multi-coil winding, wound on a magnetic wire made of ferromagnetic material. Alternating current in the wire (primary coil) creates an alternating magnetic mole, whose lines of force pass through the secondary coil, exciting an EMF in it, which is proportional to the value of current in the first coil. Thus, we can find the current in the first coil (wire) by measuring the arising EMF.
How to Measure With a Clamp Meter?
A sequence of operations when working with clamp meters:
- set the switch to the desired measuring range. If the circuit characteristics are unknown, start with the largest range;
- open the magnet wire;
- place a single conductor of AC or DC current in the internal space of the clamps and close them;
- place the clamps perpendicular to the wire or busbar;
- read the screen.
If two conductors (phase and zero) are inside the magnetic core, their magnetic fluxes are mutually compensated, and the display will show zero results. If a different value is displayed in such a situation, it indicates the presence of leaks and malfunction of the network.
A single conductor for measurements in the absence of available sections with separation of wires can be found in the switchboard or in the places where the phase wires are connected to the circuit breaker.
Design of the Clamp Meter
Modern clamp meters, regardless of the manufacturer and modification, contain the following elements: magnetic cores with a moving clamp-lever, switch for measuring ranges, screen, output connectors for probes (in this case, the clamp can be used as an ordinary multimeter) and the button for fixing current measurements (photo below).
Most modern current meters also include an internal transformer with a diode bridge. In this case, the secondary winding leads are connected via a shunt. Depending on the range of currents to be measured, current clamps can be single-handed (for voltages up to 1000 V) and two-handed with additional insulated handles (from 2 to 10 kV inclusive). Current-measuring devices designed for measurements over 1 kV have an insulator length of at least 38 cm and handles of at least 13 cm.
As a rule, the safety category and the maximum current to be measured are indicated on the device’s body. For example:
- CAT III 600 V means that the instrument is protected against short-term inrush voltages inside the equipment when used in fixed networks with voltages up to 600 V.
- CAT IV 300 V means that the device is protected against inrush voltages inside primary supply level equipment up to 300 V. An example of such equipment would be a conventional electric meter.
Useful Tips When Using a Clamp Meter
Here are some tips:
- to measure the current consumption of household appliances without opening the solid cable, you can use an adapter with separate cores;
- for a more accurate measurement of small currents passing through the flexible insulated wire, it should be passed through the magnet wire several times – wrap several turns on one side of the clamp. The value obtained on display should be divided by the number of turns;
- voltage, resistance, frequency measurements are made according to the algorithm similar to the principle of operation of an ordinary multimeter with the function switch in the appropriate position;
- to measure the power consumption, measure the current consumption and operating voltage and multiply the obtained readings. For example, for a 220V network at a current of 4A, the power P = 220 x 4 = 880 W.
Safety Rules for The Use of Clamp Meters
When using clamp meters, the safety precautions detailed in the instruction manual of each clamp meter must be strictly adhered to.
The clamp meter may only be used indoors or outdoors in dry weather. Current can be measured on insulated cables as well as bare cables. Before use, the person must wear protective gloves and place a dielectric base and special boots under the feet.
Recommendations for Safe and Accurate Measurements
1. Every measuring instrument is designed to be used under specific technical conditions and work with specific loads. These specifications should be read in advance and followed during operation.
For example, Fluke instruments are marked as CAT III 600 V or CAT III 300 V. It indicates that the electrical circuitry of the device is made with protection against short-term overvoltages in the measured network up to 600 or 300 volts, respectively.
If the limit of the measured value is unknown, the maximum value mode is set on the device.
2. The working insulation on the sliding magnet wire and the measuring tips protects the user from creating unauthorized short circuits when working under voltage. It is necessary to monitor its condition. This is especially true when measuring currents on bare, uninsulated wires.
The current clamps are measuring instruments. They must undergo periodic metrological verification in an electric measuring laboratory and have its stamp on the body or a certificate of verification, the period of validity of which is limited.
4. Since the clamp meters are used for live work, it is obligatory to periodically test the insulation layer in an electric testing laboratory with a verification report and a relevant stamp.
Without an insulation test and verification, it is forbidden by regulations to use the clamps in operation, even if they have just been purchased from the manufacturer. Damage can be caused by improper storage or transportation. The pre-sale preparation of the tool in the store is incapable of detecting any faults that may have occurred.
5. Before measuring resistances, make sure that there are no potential voltages. They may not only affect the accuracy of the readings but also damage or burn sensitive measurement circuits by the formation of dangerous currents.
6. Work with live current clamps is classified as dangerous to human life. Only trained and qualified personnel with at least a third electrical safety group is allowed to work with live current clamps.
How accurate are clamp meters?
They are very accurate, but they can be off by up to 5%.
Can you measure DC with an AC clamp meter?
No, you cannot measure DC current with an AC clamp meter. The clamp meter can’t measure DC because it is a type of current that only flows in one direction.
Can a clamp meter do the same as a multimeter?
A clamp meter cannot do everything a multimeter can do because it has only one function – voltage and current measurement.
Do I need a multimeter and a clamp meter?
A multimeter is an essential tool for any electrician. It measures voltage, current, and resistance. A clamp meter is a type of multimeter that can measure current in amperes and voltage in volts.
The answer to the question depends on what you will be doing with it. If you are going to be using it for electrical work, then yes, you will need both of these tools.
Which is better: budget multimeter or clamp meter?
The budget multimeter is the go-to tool for many professionals. It is a versatile instrument that can measure voltage, current, and resistance.
Some professionals prefer the clamp meter because it has more features than a budget multimeter and can be used for more types of measurements.
Clamp meters are usually more expensive than budget multimeters.
Related Comparison: Clamp Meter vs. Multimeter
Video Tutorial: How to Use a Clamp Meter Guide
That’s the whole instruction on how to use the clamp meter yourself. As you can see, there is nothing complicated. The main thing is to observe safety precautions and to measure carefully. We hope that our tips and video instruction clearly explain the procedure!