Clamp meters continue to evolve. Overall, there is a welcome migration of advanced capabilities from multimeters to clamp meters, said André Rebelo, global communications manager of Extech Instruments (www.extech.com/instruments), a FLIR company. New functionality of the current clamp meters, he said, make electrical work easier and safer to perform with fewer tools.

“Tool integration is a key theme of the future of test equipment, and advanced clamp models offer that future glimpse today,” he said. “Advances also have brought increased accuracy and performance expectations to clamp meters. Related to that, many more clamp meters offer true rms accuracy, ensuring that electrical readings from equipment with nonsinusoidal waveforms are as accurate as readings of clean, sine-wave power form the main source.”

Market research company Frost & Sullivan forecast two years ago that multifunctionality would be a major trend in handheld testing equipment, Rebelo said.

“That has been borne out in clamp meters with the promise of multi-functionality fully realized in today’s advanced clamp meters,” he said. “Models have been introduced that integrate capabilities typically found in separate test equipment. Examples of integrated functionality include contact and noncontact (infrared) temperature, dual-temperature measurement, noncontact voltage detector, ‘recording’ or data logging, and sophisticated data functions previously found only on multimeters. One-button differential temperature calculation can quickly identify abnormal temperatures in two components. True rms measurements expand ‘accurate versatility’ by delivering precise readings even when electrical signals are distorted by electronic or solid state components, such as newer, efficiency-oriented motor controls.

“Additionally, significant advances have been made in coordinating clamp meter readings with other essential diagnostic tools such as infrared thermal imaging cameras,” he said.

Rebelo cited several clamp meter developments and features:

• The increased prevalence of direct current (DC) power in everything from industrial motors to residential lighting has increased the need for a DC clamp meter. Having both alternating current (AC) and DC measurement in one clamp meter can be indispensable.

• Bluetooth data transmission of essential electrical readings to related tools, such as infrared cameras, increases accuracy of coordinated findings and simplifies and accelerates work by eliminating the need for notetaking.

• Mini-clamps with ultra-compact jaws make it safer to work in confined areas, such as a conduit junction or elbow.

• Safety has been increased by the increased availability of clamp meters with a CAT IV over-voltage rating for use in demanding environments. Higher current ratings also have safely expanded the capabilities of clamp meters as high as 1,500-amperes (A). Flexible clamp meters have been around for several years, but they remain useful for hard-to-reach areas and large wire bundles with current ratings upward of 3,000A.

“An entry-level clamp meter should be rated for 400A AC current, AC/DC voltage, resistance, frequency, capacitance, temperature (using a thermocouple), duty cycle, as well as diode and continuity testing,” Rebelo said. “Having a built-in voltage detector is a plus that can often be found in many basic clamp meters. It’s important to keep in mind that overall, so-called ‘standard clamp meter’ offerings have migrated upwards so that it is reasonable for an electrician to expect more from a basic clamp.

“Advanced models forge ahead as a showcase of innovation in test equipment. Bluetooth wireless technology can transmit electrical readings to a compatible thermal imager that can imprint readings right on a related infrared image. We see parallels of what’s taking place in consumer electronics—related devices are working together and ‘talking to each other.’

“Top-of-the-line models offer higher CAT IV overvoltage ratings and higher current ratings and generally are larger and more rugged with jaws that can swallow a 750 MCM conductor or two 500 MCM conductors. Faster processing permits the capture of important yet brief incidents such as inrush currents and transients.”

John Olobri, AEMC (www.aemc.com) director of sales and marketing, cited functionality and operator safety among the most significant improvements in clamp meters.

“We see more meters today meeting the CAT IV safety ratings,” Olobri said. “Several clamp-ons now offer the ability to perform power and harmonic measurements, temperature measurements, inrush and more. Multiline displays make it easier for the operator to see several variables at the same time, such as volts, amps and watts. Data communication to computers makes it easier for the operator to document test results.”

Olobri defined basic functions of clamp meters for everyday use to include measurements of volts, amps, resistance, continuity, back-lighting of the display, and a hold function. High-end models offer the ability to measure power, power factor total harmonic distortion and indi vidual harmonics, inrush, phase-rotation measurements, and the ability to do limited data logging.

Christopher Bohn, Fluke Corp. (www.fluke.com/clamps) electrical products marketing manager, said that clamp meters remain the go-to tool for electricians measuring loads, such as motors, since amperage is the most important measurement for load assessment, and a clamp meter directly measures and reads in amps, while also being able to measure voltage and other parameters.

Improvements to current clamp meters have been developed in response to electrical work environments, he said.

“Electricians reported frustration with the limitations of classic clamp jaws,” he said. “They were unable to work the jaw into tight cabinets and around large, rigid conduit. Improvements made to meet that need include flexible current probe attachments, detachable clamp jaws, and detachable remote displays.”

Bohn cited other improvements in the past few years that continued increases in safety ratings to meet NFPA 70E requirements, development of high-accuracy milliamp clamp meters for use in controls/automation, and dual AC/DC capability, now more common in response to increased DC measurement applications.

According to Bohn, a basic, safety-rated AC digital clamp meter measures amps using the current transformer built into the jaw and measures voltage using test leads. Advanced models include additional features and measurement capabilities such as inrush for capturing readings at motor startup, filters for accurately measuring variable frequency drive output, and flexible current probes or removable display technology.

“Today’s clamp meters better account for the hazard and difficulty of the live electrical work environment,” Bohn said. “The innovations previously cited allow an electrician to easily connect around the measurement point and then to remove his or her hand from the live electrical environment to take the measurement. And accuracy continues to increase, while cost has remained flat or decreased for products of far higher overall quality and feature set.”

Jim Gregorec, Ideal Industries (www.idealindustries.com) business unit manager, said that clamp meters continue to consolidate multimeter functionality and incorporate more ease-of-use features, such as auto ranging; auto zeroing; and brighter, bolder displays.

“Accuracy,” Gregorec said, “has increased slightly, while safety has been maintained at high levels with the advent of category safety ratings. Costs have increased modestly as global economies come out of the recession. I think some of today’s meters are more robust from the effects of noisy circuits and electromagnetic interference. Better shielding and frequency rejections above the 50/60 hertz fundamental have made for easier circuit troubleshooting. Low amp ranges have made it possible for larger amperage clamps (i.e., 600A/1,000A) to accurately measure currents around 1A.”

He said a basic clamp meter should be able to measure AC amperage, AC/DC voltage, resistance, and continuity in a CAT III, 600V environment.

Higher end models add measuring capabilities and ruggedness/durability.

“For example, higher end clamps can also measure capacitors on motors, frequency of voltage/current, and add DC current capability for solar and industrial measurements. Higher end models can also withstand many more voltage transients, heavy-gloved use, and overall wear and tear of the mechanical and electronic components,” he said.

Ian Bensted, Megger (www.megger.com) product manager, said that mechanics within the clamp jaw have improved, giving greater accuracy at low-current measurements.

“A number of clamp meters today have true rms, giving greater accuracy with distorted sinusoidal waveforms capability as well as a DC current function,” Bensted said. “Most have a simple-to-use function dial that renders ideal for single-handed use. Also, the features on clamps today mean very little reference to the user manual is required, as the features are self-explanatory.

“Several units are capable of voltage, resistance, capacitance and frequency, making them more a multimeter type instrument. These additional features are now accepted as the norm with prices remaining much as they were two years ago. CAT safety ratings in a few models are now up to CAT IV, 600V.”

With the selection of clamp meters available today and the additional features they offer, Bensted said it is difficult today to define a basic clamp meter.

“A prospective buyer for a basic clamp meter generally is only too happy to find their purchase is capable of additional functions if required,” he said. “Today a clamp meter is usually chosen for its additional features versus cost.”


GRIFFIN, a construction and tools writer from Oklahoma City, can be reached at 405.748.5256 or up-front@cox.net.