A clamp-on meter, also known as a clamp meter or current clamp, is a versatile electrical testing device designed for non-intrusive measurement of electrical current. Unlike traditional meters, it features a hinged ‘clamp’ jaw that can be placed around a conductor, allowing users to measure current without the need for direct contact.
Widely used by electricians and technicians, clamp-on meters provide a safe and convenient way to assess current flow in electrical circuits, making them an essential tool for troubleshooting, maintenance, and electrical diagnostics.
Best Clamp Meter for Electricians
The Fluke 375 Clamp Meter is the best digital clamp-on meter we tested. We will have more options and detailed reviews later in this article, however, if you are short on time you can’t go wrong with this meter.
Types of Clamp Meters and How They Work
There are two main types of clamp meters available in the market today, which are based on the types of the measured current. They are:
- Current-Transformer Clamp Meter: can only measure AC current
- Hall Effect Clamp Meter: can measure both AC and DC currents
Current-Transformer Clamp Meter
A current-transformer clamp meter uses two ferrite iron clamps that are independently wrapped with copper coils. The main principle is that the combination of ferrite iron and copper coils forms a magnetic core, which allows the measurement to happen.
When the arm of the clamp meter is placed on a conductor, the magnetic wave generated from the clamp meter acts as the secondary winding, of which the iron core of the clamp concentrates the magnetic field of the conductor (or cable).
Due to this action, a new current in proportion to the primary current is generated by electromagnetic induction. This new current is what actually measured by the measurement device inside the clamp meter, which will produce the current reading.
Hall Effect Clamp Meters
Hall effect clamp meters also utilize two ferrite iron clamps. The main difference is that these clamps are not wrapped with copper coils. Instead, in hall effect clamp meters, the current flowing through the conductor is concentrated in the one or more gaps of the ferrite iron core, whenever the clamp jaws close around the cable or the conductor.
If we look closely at the clamp tips of hall effect clamp meters, we can see at least one gap between the two jaws in the clamp’s core. This gap creates an air pocket that is passed by the magnetic field of the conductor. This will also limit the magnetic flux and so ensure the core won’t be saturated by the magnetic field.
Inside the gap is a semiconductor unit we call a hall effect sensor, which is covered with a plastic molding (so we can’t see it). The hall effect sensor is essentially a variable-voltage transducer that can adjust its output voltage based on the conductor’s current. The voltage generated by the sensor is then amplified and scaled to represent the measured current.
Since the clamp’s core and the gap are able to concentrate on DC magnetic fields, hall sensor clamp meters can also measure DC current.
How To Measure Current Using a Clamp Meter
Although different clamp meters might have their own unique features and measurement methods, here are the general steps in using a clamp meter to measure current:
- If the probes are attached to the clamp meter, remove them first
- Switch the clamp meter ON
- If you can choose between AC or DC current, make your choice using the dial switch. After that, the display should indicate that it’s now ready to measure current. Typically the display should show a jaw sign or similar icons.
- Place the conductor in the center of the clamp, then close the clamp’s jaws. Level the conductor between the alignment marks that should be on the jaws.
- The display should now show the desired reading. Depending on your model, you can change the display’s resolution based on your needs.
Important Features To Consider in a Clamp Meter
RMS stands for root mean square, and if your clamp meter comes with a true RMS feature, it simply means the meter can convert AC signals into DC signals of equivalent value. So, a true RMS meter can accurately measure pure waves, as well as non-sinusoidal waves.
AC current is represented as a sine wave because it reverses directions several times per second (alternating). On the other hand, the amplitude of a sine wave will change continuously over the wave period, and so current measurements will vary depending on when you measure this sine wave, and so it might not be accurate.
True RMS simply tackles this accuracy issue.
IP, or Ingress Protection rating will tell us the degree of enclosure protection employed by the clamp meter unit, especially against water, moisture, and other external factors. A well-protected instrument means we can use it in more places and conditions. Some models use NEMA instead of IP rating.
Auto-ranging clamp meters can automatically set the correct measurement range. So, users wouldn’t need to adjust the switch and dial positions while trying to properly clamp the conductor. Auto-ranging feature, simply put, will save time and improve the unit’s ease of use.
Different clamp meter units come with different display units. The display can come in different sizes, resolutions, and some might have back-light and some don’t. The better the display, the easier we can view and analyze the readings.
The unit’s internal memory. The more memory it has, the more measured values can be recalled later.
The inrush feature provides users with an accurate measurement of current surges/spikes that typically flow into electric appliances and motors during startup. Inrush can be a very important feature to have when troubleshooting various appliances.
Why You Need a Clamp Meter: Pros and Cons
First, let us discuss the benefits of using a clamp meter:
- Clamp meters filter out noise, and can provide accurate and stable readings for various applications.
- Versatile, can be used in noisy electrical situations and environments
- Typically slim and ergonomics, so we can easily hold it when wearing protective gloves
- Most models can measure low-level DC current
- Fast measurements, so can save time
- Newer clamp meters come with extra features for a wide range of measurements
However, there are also several limitations of clamp meters in electrical measurements:
- It is mainly a current-measuring tool, so not all models can measure voltage accurately
- Measures to the nearest tenth or hundredth of a unit. On the other hand, digital multimeters can measure in milliunits (millivolts, milliamps, and milliohms), so DMMs are generally more precise.
Best Clamp-on Meters for Electricians
Below, we will review the best clamp meters for electricians we have used and tested. Each of them has their own advantages and disadvantages, and more importantly, price points. Without further ado, let’s rundown the list of the best clamp meters for electricians.
#1. Fluke 375 AC/DC TRMS Wireless Clamp
- Weight: 1.10 pounds
- Size: 9.685 in. x 3.267 in. x 1.692 in.
- Measure AC/DC current via the clamp
- Features a VFD low-pass filter which provides accurate motor drive measurements
- Connects wireless to any smartphone over Bluetooth
- CAT-III to 1000V, CAT-IV to 600Vclass 2, double insulation safety rating
- 600 A ac and dc current measurement
- 2500 A ac current measurement with (optional) iFlex flexible current probe
Pros and Cons
- Durable and sturdy with a high drop rating.
- True-rms voltage and current for accurate measurements on non-linear signals
- Bluetooth connectivity keeps you away from the arc flash zone
- Transmit measurements wirelessly via the Fluke Connect app or Fluke Connect Assets software
- Create reports and share with your team without leaving the field
- Line splitter feature included
- Double insulated for extra safety
- Back-lit display
- The included case is small and won’t hold all accessories
#2. Klein Tools CL800 Digital Clamp Meter
- Weight: 12.3 oz
- Size: 9 in. x 3.8 in. x 1.5 in.
- Jaw size: 1.38 in.
- True RMS measurement with auto-ranging
- Can perform continuity and frequency
- Can measure voltage, resistance, capacitance, and frequency
- Low-impedance mode to pick up ghost voltages
- Temperature measurements via the included thermocouple
- CAT-IV rating at 600V
Pros and Cons
- Pretty accurate measurement for AC and DC amperage and voltage
- Versatile with various multimeter ranges, including capacitance
- Flashlight function
- Temperature input (thermocouple included)
- Durable and sturdy build
- Backlit illuminated display
- Easy to use with fixable probe leads
- Non-contact voltage checker feature
- Can take a while to get readings
- At certain range and angles, the screen is prone to washing out with backlight
#3. Fluke 324 True RMS Clamp Meter
- Weight: 7.3 oz
- Size: 8.1 in. x 3 in. x 1.3 in.
- True RMS measurement provides accurate readings, can measure both linear and non-linear loads, regardless of waveforms
- Measures AC current up to 400A, resistance to 4kiloohms, and AC/DC voltage to 600V
- Jaw opening can measure current in a conductor up to 30 mm without touching and/or interrupting the circuit
- CAT IV installations to 300V and CAT III installations to 600V
- Slim and ergonomic design
- Large back-lit display
Pros and Cons
- Compact and ergonomics
- Can measure AC and DC voltages up to 60V limit
- Audible continuity sensor
- Large backlit display
- Versatile set of features
- Can measure temperatures with included thermocouples
- Lacks analysis in low temperature
We hope you have gathered enough information here to make an informed decision. If a more traditional meter is what you are looking for, we recommend you check our digital multimeter guide.
Be sure to check back often and consider becoming a member of the website. Membership is free register today!