The Klein Tools CL390 represents a compelling middle-ground option in the digital multimeter market, balancing professional-grade features with DIY accessibility. This versatile clamp meter offers AC/DC measurement capabilities, auto-ranging functionality, and additional features like temperature measurement and capacitance testing—all at a price point significantly lower than premium competitors. While it delivers excellent value and reliability for most users, the reverse-contrast display presents visibility challenges in bright outdoor conditions, and some operational quirks may frustrate specific user groups. Overall, it’s a solid investment for both DIY enthusiasts and professionals who need comprehensive electrical measurement capabilities without premium pricing.
Introduction
In today’s increasingly DIY-focused world, having reliable electrical testing equipment has become essential for homeowners, hobbyists, and professionals alike. The Klein Tools CL390 Digital Clamp Meter positions itself as a versatile solution for those needing comprehensive electrical measurement capabilities without investing in ultra-premium equipment. This review examines how well this multi-functional device delivers on its promises and whether it justifies its position in Klein’s product lineup.
Design and Build Quality
Physical Construction
The CL390 immediately conveys a sense of durability that Klein Tools products are known for. While not as rugged as some industrial-grade models, the meter features solid construction with high-quality plastic housing that can withstand the inevitable bumps and drops encountered in real-world usage. The unit is larger than some competing models, which contributes to its substantial feel in hand.
The clamp mechanism operates smoothly with sufficient spring tension to maintain proper contact during measurements. Some users noted that the spring might be slightly too strong, requiring additional hand strength to open fully, but this ensures secure closure around conductors during testing. The thumb-operated rotary selector dial provides satisfying tactile feedback, allowing for easy one-handed operation—a crucial feature when working in tight spaces.
Ergonomics
The ergonomics of the CL390 are generally well-considered. The probe holder built into the side of the clamp is particularly useful, essentially providing a “third hand” that allows single-handed operation in many scenarios. This thoughtful addition significantly improves usability in confined spaces where extra hands aren’t available.
The button placement is intuitive, though some users report that the side-mounted buttons occasionally require a firmer press than expected. The unit’s weight balance feels appropriate, neither too heavy for extended use nor too light to feel insubstantial.
Features and Functionality
Measurement Capabilities
The CL390 offers an impressive range of measurement capabilities that cover most electrical testing scenarios:
- AC/DC voltage measurement (up to 600V)
- AC/DC current measurement via clamp (up to 400A)
- Resistance measurement
- Continuity testing with audible indicator
- Capacitance testing
- Frequency measurement
- Temperature measurement (via included thermocouple)
- Non-Contact Voltage Testing (NCV)
- Diode testing
The inclusion of both AC and DC amperage measurement via the clamp is particularly noteworthy, as many competing models at this price point only offer AC current measurement. This feature makes the CL390 especially valuable for those working with solar installations, automotive systems, or other DC applications.
Auto-Ranging
The auto-ranging functionality works efficiently, automatically selecting the appropriate measurement range without requiring manual adjustment. This feature streamlines testing procedures and reduces the likelihood of measurement errors. For users who prefer manual control, the range button allows for precise range selection when needed.
Special Features
The relative zero function is particularly useful for DC current measurements, allowing users to zero out ambient electromagnetic interference for more accurate readings. The MAX/MIN recording feature captures peak values—extremely valuable when monitoring motor startup currents or other transient electrical events.
The non-contact voltage detection feature provides a quick safety check before handling potentially live circuits, though some users noted it may be overly sensitive in certain environments.
Display and Visibility
The display represents both a strength and weakness of the CL390. The reverse-contrast LCD (white digits on a black background) provides excellent visibility in low-light conditions and indoor environments. The backlight offers two brightness settings, which further enhances readability in dimly lit situations.
However, numerous users consistently report difficulty reading the display in bright outdoor conditions, particularly in direct sunlight. This limitation represents a significant drawback for professionals who frequently work outdoors, such as HVAC technicians servicing exterior units or electricians working on outdoor installations. Despite Klein’s claims of “improved viewability in all lighting conditions,” real-world experience suggests otherwise.
The display size itself is generous, with large, clear digits that are easy to read when visibility conditions are favorable. The additional indicators and symbols are well-organized and provide clear status information without cluttering the screen.
Performance and Accuracy
Measurement Accuracy
For its price point, the CL390 delivers commendable accuracy across most measurement functions. When compared against reference voltage sources, users report the calibration is generally spot-on. The True RMS (Root Mean Square) functionality ensures accurate readings even with non-sinusoidal waveforms, which is essential when working with modern electronic equipment.
The DC current measurement via the clamp—using Hall effect sensors—provides good accuracy for readings above 0.3A, though some users report limitations when measuring very low currents (below 300mA). This limitation is clearly stated in the manual but may disappoint automotive technicians looking to diagnose parasitic battery drains, which typically fall in the 30-100mA range.
Temperature measurements through the included thermocouple are reasonably accurate for non-specialized applications, though dedicated temperature instruments will naturally provide better precision for critical temperature-dependent diagnostics.
Consistency and Reliability
Long-term users report consistent performance without significant drift in measurements over time, indicating good component quality and calibration stability. The meter’s response time is appropriate for most applications, quickly stabilizing on readings without excessive fluctuation.
Power Management
The CL390 is powered by three AAA batteries (included) and incorporates power-saving features to extend battery life. The auto power-off function turns the meter off after approximately five minutes of inactivity—a feature that draws mixed reactions from users.
While this feature preserves battery life, numerous users express frustration with the implementation, particularly because the meter may shut down during extended monitoring periods even when actively taking measurements. The warning beeps before auto-shutdown can also be distracting in quiet work environments.
However, as several reviewers point out, the instruction manual describes how to disable this feature by holding the SEL/NCV button while powering on the meter—information that seems to have escaped many users’ attention. This highlights the importance of thoroughly reading the included documentation.
Included Accessories
The CL390 package includes:
- The meter itself
- Test leads with removable probe tips (rated for 2000V)
- Temperature probe (thermocouple)
- Carrying case
- Batteries (3× AAA)
- Instruction manual
The included carrying case receives mixed reviews—some users appreciate its inclusion but criticize its thin construction and relatively basic design compared to cases included with previous Klein models. The test leads are of good quality with a versatile design that allows for both long and short probe tips.
The thermocouple temperature probe appears to be the accessory most prone to damage, with several users reporting broken probes shortly after purchase. This suggests a potential quality control issue with this specific component.
Notably, the magnetic hanger accessory is not included but available as a separate purchase—an addition many users recommend for hands-free operation.
Usability for Different Applications
Residential Electrical Work
For home electrical projects, the CL390 excels. Its voltage and current measurement capabilities are more than adequate for troubleshooting household circuits, checking outlet voltages, and verifying proper appliance operation. The non-contact voltage detector provides a quick safety check before beginning work on potentially live circuits.
HVAC Applications
HVAC technicians will appreciate the temperature measurement capability for checking system temperature differentials and the capacitance testing for diagnosing faulty run or start capacitors—common failure points in air conditioning systems. The current measurement range covers most residential HVAC equipment needs, though as mentioned, the minimum measurable current of 0.3A may be limiting for some specialized applications like measuring very low-draw inducer motors.
Automotive Diagnostics
For automotive applications, the results are mixed. The DC voltage measurements are perfect for battery and charging system diagnostics, and the DC amperage clamp is excellent for checking alternator output or verifying solar panel performance. However, the inability to accurately measure currents below 300mA limits its usefulness for parasitic drain testing—an important diagnostic procedure for vehicles with battery drainage issues.
Solar and Renewable Energy
The CL390 is particularly well-suited for solar installation work due to its DC current measurement capabilities. Technicians can quickly verify panel output without disconnecting wires, significantly streamlining the testing process.
Electronics Hobbyists
For electronics hobbyists, the meter offers good versatility with its microamp measurement capabilities (via leads, not clamp), resistance testing, and continuity checking. The capacitance testing feature is also valuable for component verification, though serious electronics work might require additional specialized equipment.
Operational Quirks and Limitations
Several operational aspects of the CL390 consistently appear in user feedback as minor irritations:
- The AC/DC selection requires pressing the SEL button rather than having separate dial positions. For users who primarily work with DC systems, this means an extra button press with every measurement.
- The auto power-off feature, while configurable, defaults to an active state and can interrupt extended testing sessions.
- The reverse-contrast display, while excellent in low-light conditions, presents visibility challenges in bright environments.
- The minimum current measurement capability of 0.3A (300mA) via the clamp limits certain specialized applications.
None of these issues represent fatal flaws, but prospective buyers should consider whether these limitations might impact their specific use cases.
Value Proposition
When evaluating the CL390’s value, it’s important to consider its position in the market. At approximately one-third to one-quarter the price of comparable Fluke models with similar features, the Klein offers exceptional value while maintaining good accuracy and build quality.
For professional daily use in demanding environments, premium brands may justify their higher cost through slightly better durability, accuracy, and support. However, for the vast majority of users—including DIY enthusiasts, maintenance personnel, and even many professionals—the CL390 represents an excellent balance of capability and affordability.
Pros and Cons
Pros:
- Excellent feature set including both AC and DC current measurement
- Good build quality and ergonomics
- True RMS measurement for accurate readings with modern electronic equipment
- Comprehensive measurement capabilities including temperature and capacitance
- Significantly more affordable than premium competitors
- Useful additional features like probe holder and relative zero function
- Good accuracy for most common applications
Cons:
- Display difficult to read in bright sunlight
- Auto power-off function can be frustrating (though disabling is possible)
- Minimum clamp current measurement of 0.3A limits some applications
- Temperature probe durability issues reported by some users
- Extra button press required to switch between AC and DC modes
- Carrying case quality could be improved
Conclusion
The Klein Tools CL390 AC/DC Digital Clamp Meter delivers impressive functionality at a competitive price point. Its comprehensive measurement capabilities, solid build quality, and thoughtful features make it suitable for a wide range of applications from DIY home projects to professional electrical, HVAC, and solar installation work.
While not without limitations—particularly regarding outdoor display visibility and some operational quirks—these drawbacks are reasonable compromises given the significant price advantage over premium competitors. For users who don’t require the absolute highest precision or durability for daily professional use in harsh environments, the CL390 represents one of the best values in its product category.
The meter particularly shines for those working with both AC and DC systems, where its dual-mode clamp functionality eliminates the need for separate testing equipment. Solar installers, automotive enthusiasts, and maintenance personnel will find its capabilities especially well-matched to their needs.
Ultimately, the Klein Tools CL390 successfully bridges the gap between basic consumer-grade testing equipment and premium professional instruments, offering capabilities that exceed its price point and reliability that inspires confidence in its measurements. For most users, it represents not just a good value, but a genuine enhancement to their technical capabilities and efficiency.
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