Clamp Meters

AEMC clamp-on Model 407 is rated at 1,000V CAT IV for all electrical environments.
AEMC clamp-on Model 407 is rated at 1,000V CAT IV for all electrical environments.
Published On
Dec 13, 2019

Clamp meters provide a convenient way to measure current without breaking the circuit, which is ideal for troubleshooting. The user simply clamps the meter around cables, wire or other conductors at any point in an electrical system, and the current is measured.

AEMC, Dover, N.H.

Director of Sales and Marketing John Olobri said, while a basic clamp meter consists of a set of jaws that go around a conductor in order to measure the current, input banana jacks on some models allow associated circuit voltage to be measured too. Both present readings on integral screens. The instruments typically can measure AC and DC voltage with DC current capability at an added cost.

“Perhaps the biggest improvement on today’s models is connectivity via Bluetooth or Wi-Fi,” Olobri said. “Other advances include recording capability and downloading via software program, higher voltage and current readings, the ability to measure harmonics, safety via higher CAT ratings and two- and three-line displays.”

Olobri said questions to consider when selecting a clamp meter include: Where will the instrument likely be used? Will measuring DC current be a requirement? What current levels? What voltage levels? Will a record of readings be needed? Is temperature a useful function? Are power and harmonic measurements going to be needed?

“Utilities and project owners are very safety- conscious,” Olobri said. “Therefore, CAT IV 1,000 Volt ratings are becoming more important.”

Flir, Wilsonville, Ore.

Flir’s CM2275 combines thermal imaging with electrical measurements.
Flir’s CM2275 combines thermal imaging with electrical measurements.

Director of Instruments Marketing Richard Wexler said accuracies of clamp meters have not changed in recent years, and learning to use new models is very intuitive.

“A selection knob permits quick setup for measurements,” he said. “And multifunction capabilities have changed—clamp-on current meters now can measure voltage, capacitance, resistance, check diode operation and infrared guided measurement.”

Primary considerations for evaluating clamp meters include accuracy, service and support, selection of amperage rating, Bluetooth communications with [infrared] camera and mobile software and what other measurement it can make.

“Minimum requirements for a clamp-on meter would be RMS current and voltage measurements,” Wexler said.

Fluke Corp., Everett, Wash.

Fluke 376 FC true RMS clamp meter connects to smart phones with Fluke Connect.
Fluke 376 FC true RMS clamp meter connects to smart phones with Fluke Connect.

“A clamp meter can be one of the most versatile devices on an electrician’s tool belt,” said Yinzi Liang, DMM/clamp product manager at Fluke Corp. “They make jobs safer, faster and provide better information than ever before. With wireless data collection and transfer, they also can help improve maintenance and installation tasks.”

Liang said clamp meters typically allow measurements of much higher values than through direct connection.

“In-series measurements typically are limited to 10 amps (A),” Liang said. “Measurements through a current clamp or a flexible current sensor can measure as much as 2,500A. Most clamp meters available today also include test leads for measurements of voltage, resistance, continuity, frequency and other parameters.”

Flexibility for improved access, storage and communication of measured values are two differences in today’s clamp meters compared to earlier versions.

“Clamp-on meters now include flexible probes, which can be snaked through a tightly packed bundle of cables for easier access than with a rigid clamp jaw,” Liang said. “This provides far better access to a specific conductor [that] needs to be tested. It also improves safety, as the user is not trying to force or twist a bulky clamp into a cramped wiring cabinet.”

These clamps enable users to save, share and analyze test results.

“Making a measurement is one thing,” Liang said. “Being able to interpret what that measurement means and act upon that data is a far more useful activity. Clamp meters that can wirelessly send measurements to smart phones, tablets and the cloud provide maintenance teams with valuable data that improves the overall maintenance and repair process.”

Safety is always the top priority, and a clamp or flexible probe offers significant safety advantages over an in-series measurement.

“First and foremost, follow all safety procedures as defined in NFPA 70E, starting with the appropriate personal protective equipment. Since the majority of measurements made by a clamp meter (voltage and current) must be made on energized equipment, matching the right tool to the right job is critical. Tools should carry IEC ratings of CAT III 1,000V or CAT IV 600V. Always make sure that the clamp or probe is rated for the appropriate level of current or voltage expected in a given situation,” Liang said.

Greenlee, Rockford, Ill.

Greenlee CMF 110 clamp meter.
Greenlee CMF 110 clamp meter.

Product Manager Youssef Takhchi said today’s clamp meters can be more accurate, are easier to use and allow the electrician to do more than just measure amperage to get the job done more efficiently, compared to earlier models.

“Clamp meters, similar to other tools that interact with electricity, are designed to be used in specific applications. Therefore, choosing a clamp meter that is rated for the job following the International Electrotechnical Commission measurement categories is crucial to avoid inaccurate measurements or possible injuries,” Takhchi said. “True RMS and auto-ranging display are considered basic capabilities nowadays that every clamp meter should offer.”

The main criteria for selecting a basic clamp meter are maximum amperage, safety category, jaw dimensions and display resolution, he said. For users looking at multifunctional clamp meters, resistance, temperature, data logging and power factor should be considered.

“In addition, selecting tools that meet IEC and UL requirements provide assurance that a high level of protection is being achieved, which is why we independently test and certify to meet these standards. Safety procedures as established by OSHA should always be followed when performing a job,” Takhchi said.

Ideal Industries, Sycamore, Ill.

Ideal camp meter TightSight display provides easy viewing.
Ideal camp meter TightSight display provides easy viewing.

Sales Engineer Dave Kadonoff said there is a continuing trend for consumers to buy the least expensive products, which has resulted in aggressive competition among suppliers vying for that market segment.

“This applies to clamp meters but know that any clamp meter should at a minimum provide AC and DC voltage to 600V, AC current to 400A, resistance to 40,000 ohms, audible continuity and a built-in flashlight. For safety reasons, a minimum of a CAT III 600 rating and a recognized independent listing with UL or other certification lab is highly recommended,” Kadonoff said.

He said knowing the exact requirements for the total measurement ranges, accuracies that will be required and the environment where the meter will be used helps ensure the product will meet needs and make work easier.

“The most recent addition to clamp meter capabilities is Bluetooth connectivity to smart phones,” Kadonoff said.

Klein Tools, Lincolnshire, Ill.

Klein CL380 digital  noncontact clamp meter.
Klein CL380 digital noncontact clamp meter.

Product Manager Sabrina Kalsi said a clamp meter can measure large AC current because of the clamp’s ferrite iron core.

“It measures the magnetic field of the current, which is then converted into an AC current reading by the meter. Some clamp meters also measure DC current [by] utilizing a Hall Effect sensor to measure the magnetic flux,” she said. Digital technology has allowed new features that improve users’ experiences. For example, back lighted LCDs for visibility in low light, auto-range for quick, easy measurements, hold, maximum, minimum and relative options to easily review data auto power-off and a battery indicator to manage power.

“A significant improvement in safety is that International Electrotechnical Commission safety standards ensure the meter meets the voltage rating for the environment. For electrical products, the CAT rating shows the meter has been designed to withstand the voltage in the rated electrical environment. For example, a CAT III 600V meter can work with indoor measurements and electrical panels, whereas a CAT IV 600V meter can also be used with outdoor and underground electrical lines. Using the right meter for the electrical application allows the user to take measurements without fear of harm,” Kalsi said.

While the basic functions of clamp meters include measuring voltage, current and resistance, additional specialty functions are available to meet the different applications.

Kalsi said these include a noncontact voltage tester, DC micro amps, in-rush current, capacitance, continuity, frequency, duty cycle, diode test, low impedance, temperature and more.

“We strongly recommend adding true root mean square to a meter’s minimum capabilities,” she said. “TRMS accurately measures both sinusoidal and nonsinusoidal waves. Meters without TRMS work on averages that add a high percentage of error when measuring nonsinusoidal waves. Sources of nonsinusoidal waves are increasing—variable speed motors, electronic ballasts, solid state, HVAC, etc. For this reason, we suggest adding TRMS to your meter’s capabilities.”

Megger, Eagleville, Pa.

Megger DCmn 500 measures DC and AC current to 1,500A.
Megger DCmn 500 measures DC and AC current to 1,500A.

Senior Applications Engineer Jeff Jowett said clamp meters today provide increased current measurement ranges into medium-voltage applications such as solar testing, improvements in jaw size and contours that increase the variety of test sites that can be conveniently clamped and improvements in the general quality of plastics that make the instruments more rugged.

Over a few decades, Jowett said, clamp-on ammeters have evolved from specialty items to core toolbox instruments that not only provide the critical benefit of saving time but also meet high-quality accuracy and range demands.

When evaluating clamp meters to purchase, Jowett said make sure the instrument fits the application.

“An inexpensive, basic function model may be all that is required. Why pay extra for functions that will not be used, such as frequency measurement, data storage and other esoteric features? On the other hand, be sure to get everything that will be needed—multifunction models are available. Assess future work requirements as thoroughly as possible and select a tester that has all the functions plus the ranges that will need to be covered. Where earth leakage measurement is to be performed, appropriate clamps are typically dedicated to that job,” Jowett said.

About the Author

Jeff Griffin

Freelance Writer

Jeff Griffin, a construction and tools writer from Oklahoma City, can be reached at

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