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What is a Clamp Meter and How is It Used to Test Current in a Circuit?

Clamp meter measurement

The clamp meter, which is also known by its lesser-used name, the Tong Tester, is an instrument used to measure current without connecting it to a circuit in series. You can operate and use this equipment without any inconvenience to measure a live conductor without damaging it or causing power loss. 

In this article, we will discuss the clamp meter in detail. What exactly is a clamp meter? How does it work? We’ll also discuss the two main types of clamp meters and applications of the clamp meter. In a recent article, we discussed the differences between all the different types of meters.

Without further ado, let’s hop into the topic and get started. 

What is a Clamp Meter? 

A clamp meter is a device that is used to measure current conveniently and safely. It is very efficient in measuring current without using test leads. To measure current, all you have to do is place a wire in the clamp meter’s claws. When current flows through a conductor, a magnetic field is generated. This device helps to detect the magnetic field so that the corresponding current reading can be provided. Dedicated clamp meters do just one thing – measure current, but most technicians carry combination clamp meters that also function as their multimeter (like with the popular Fieldpiece meters)

Measurements are performed quickly and safely without interrupting the flow of current and without the need for test leads.

Working Principle of Clamp Meter 

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A clamp meter works on the magnetic induction principle to measure AC without contact. Like every conductor, the current flowing through a wire produces a magnetic field. The Hall Effect sensor detects the magnetic field created by current flow to create less voltage across the sensor. We can say that this sensor mainly detects magnetic fields that are caused by low current flow. 

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Parts of Clamp Meter 

The clamp meter has various parts, and most of these are found on any modern generation clamp meter:

  1. Transformer Clamps (Jaws) – Jaws detect the magnetic field produced due to current flow. 
  2. Clamp Opening Trigger – As the name indicates, the trigger is used to open and close transformer jaws.
  3. Power Switch – You can use the power switch button for turning the clamp meter on or off. 
  4. Back Light Button – When you press the backlight button, the LCD is illuminated so that the displayed value may be easily read in dark places or at night. 
  5. Hold Button – The value displayed on display can be held by pressing this button.
  6. Negative/ Ground Input Terminal – The meter cable’s negative/grounding jack is joined to this cover (on combo clamp/multimeters)
  7. Positive Input Terminal – The meter cable’s positive jack is joined to this cover.
  8. LCD Display – There is a display panel at the clamp meter to check the measured values.   
  9. Functional Rotary Switch – This enables the user to choose between different currents for measurement. Modern clamp meters can measure voltages, continuity, and resistance. So, this rotatory switch allows you to switch between different measurement modes. 

Types of Clamp Meter 

The two significant types of clamp meters are: 

  1. Current Transformer Clamp Meter- AC measuring device 
  2. Hall Effect Clamp Meter – AC and DC measuring device

Current Transformer Clamp Meter: 

Two clamps made from Ferrites Iron are used in current transformer metering. Copper coils separately cover these clamps. Combined, they form a magnetic core on the surface of which the measurements are taken.

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According to the Electromagnetic principle, a current in a conducting material causes magnetic flux to form. The magnetic field can be measured by magnetic flux, a unit of charge.  Greek letter Phi () is used to represent it. 

Hall Effect Clamp Meter

Both AC and DC signals can be measured by Hall effect clamp meters. A Hall Effect clamp meter contains a concentrating magnetic field when the clamps are closed around the conductor, induced by current flowing through the conductor.

With the Hall Effect Clamp meter, you can measure DC too since it can concentrate DC magnetic fields. These clamp meters must be zeroed when measuring the current. It is necessary to avoid errors arising from the Earth’s magnetic field or any other magnetic field sources in the vicinity. 

Major Applications of Clamp Meter 

The clamp meter is of much significance in both industrial and commercial aspects. Some of the standard applications of the clamp meter are as follow: 

  1. These digital meters are used primarily to measure very high currents. Current above 10A can not be measured by these meters for more than 30 seconds without damaging them. 
  2. Commercial, industrial, residential electrical systems & HVAC use these meters the most. 
  3. Accessible systems are repaired using these as per the requirement. 
  4. Technicians and engineers use clamp meters for troubleshooting electrical instrument fixing problems, executing last circuit tests etc. 
  5. It is also used for supervising a beginner electrician while fitting electrical instruments. 
  6. The clamp meters are used for both scheduled and emergency maintenance as well as troubleshooting. 


Is a clamp meter better than a multimeter? 

A multimeter usually measures voltage, resistance, continuity, and sometimes low current, while a clamp meter is specially designed for measuring current. One of the significant factors in the clamp versus multimeter difference is that the clamp meter can measure high currents. If we talk about accuracy, the multimeter is more accurate and reliable. Both are best in their ways. Measuring current with a multimeter requires the meter to be placed in series in the circuit, something that isn’t always possible as it means de-energizing the system.

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How accurate is a clamp meter? 

Accuracy is usually pretty good with these meters. However, when it comes to DC clamp meters, anything less than 10 amps is not accurate. You can improve the accuracy of a clamp meter significantly by adding 5-10 turns of wire. Once you have acquired the low current, run it through this wire. The reading will be accurate. 

Can a clamp meter measure Watts? 

The clamp meter is used to measure alternating current on live circuits. It measures the current in Amperes. The clamp meter does not measure in Watts, as it is the unit of Power but it is easy to calculate the wattage thanks to Ohm’s law; P=V*I or Wattage = voltage * current. So, if your clamp meter measures 40 Amps on a 110 Volt circuit, the wattage is 4,400.