Buy the Fluke 325: it reads small loads in 0.01 A steps, tests capacitors and temperature, and has a two-year warranty. Get the Klein CL390 for a thermocouple in the box, or the CL710 for a CAT IV 600 V rating.
Top pick: Fluke 325$299.49 at AmazonPrice as of Oct 24, 2026, 5:30 AM EDT
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.com at the time of purchase will apply to the purchase of this product.
How the four compare on our spec score
Five checks from each maker’s datasheet or manual, equal weight. The rules and every input are in the method section near the end.
PlumbingPicks spec score out of 10, from Fluke’s and Klein’s datasheets, manuals and product pages, read Oct 22, 2026. It is not a customer rating or a lab test of our own.
All four are handheld, true-rms clamp meters that read AC current through the jaw and voltage and resistance through test leads. All four carry a two-year warranty in writing.
The spread comes from three things a plumber uses: a low amp range for small loads, a capacitance function for pump capacitors, and a temperature input. The Fluke 323 has none of the three, which is why it trails.
Each pick, in detail
What each maker’s sheet says, what it means on a plumbing call, and where each one fell short on our checks.
400 A AC/DC600 V AC/DC±(2% + 5 digits) AC A40 kΩ1000 µFCAT III 600 V
Buy it if
You test water heater elements, well pumps and their capacitors, and want one meter that covers all three.
Skip it if
You want a probe and case in one box. The Klein CL390 ships with its thermocouple.
The Fluke 325 is the clamp meter I’d hand a plumber who works on electric water heaters and well pumps, and I’ve used it. It’s sold by Amazon.com, and it has the most functions in Fluke’s 320 Series, the 323, 324 and 325.
What sets it apart on our work is the low range. Fluke’s datasheet lists AC current ranges of 40.00 A and 400.0 A, so a 4,500 W element’s 18.75 A draw shows in 0.01 A steps. The 323 reads in 0.1 A steps only.
AC current accuracy is ±(2% + 5 digits) from 45 to 65 Hz. At 18.75 A that works out to about ±0.43 A, by our math from Fluke’s figures.
Capacitance runs on 100.0 µF and 1000 µF ranges through the test leads. That’s the function you’d use on the capacitors in a well pump control box, and it scored a 10.
Contact temperature reads from 14 to 752°F, another 10. Fluke lists the meter, test leads, soft case and manual in the box, with no temperature probe, so plan on buying one.
It’s the only one of Fluke’s three that measures DC current, to 400 A, and frequency from 5 to 500 Hz. It adds Min/Max, which the 323 and 324 lack.
Safety is rated CAT III 600 V and CAT IV 300 V, a 9 on our check. The jaw takes a wire up to 30 mm (600 MCM). Resistance reads to 40 kΩ, with continuity at 30 Ω or less.
The warranty is two years, printed on the datasheet. The meter weighs 283 g and has a backlight, which helps in a dark utility closet.
My call: if you buy one meter for water heaters, pumps and controls, buy this one.
Best for a thermocouple in the box
Klein Tools CL390 AC/DC digital clamp meter, 400 A
400 A AC/DC600 V AC/DC±(2.0% + 9 digits) AC A40 MΩ4,000 µFCAT III 600 V
Buy it if
You check pipe and tank temperatures as often as amps, and want the probe in the box.
Skip it if
You test at the service entrance. Its rating is CAT III 600 V; the CL710 carries CAT IV 600 V.
The Klein CL390 is the one with a thermocouple in the box, and I’ve used it. It’s sold by Amazon.com. Klein’s product page lists a carrying case, test leads, the thermocouple and batteries with the meter.
Its manual lists AC current on 40.00 A and 400.0 A ranges, with 0.01 A steps on the low one. Accuracy is ±(2.0% + 9 digits), about ±0.47 A at a 4,500 W element’s 18.75 A, by our math.
One habit to learn: the low range is a separate dial setting. Klein’s manual says to turn to the 4/40A setting for better resolution when the reading is under 40 A.
Temperature runs from −40 to 1,832°F through a K-type thermocouple plugged into the meter’s jacks. That’s a 10, and it’s the reason I’d pick this one over the CL710.
Capacitance runs from 40.00 nF up to 4.000 mF, which is 4,000 µF. DC microamps read to 200 µA, and resistance to 40.00 MΩ.
Safety is CAT III 600 V, Class 2, double insulated. That’s an 8 on our check. Klein’s manuals define CAT III as the building’s distribution side and CAT IV as the source of the installation.
The jaw opens 1.6 in, the widest of the four. Klein rates it for a 6.6 ft (2 m) drop, and the non-contact voltage tester is built into the jaw.
The display is a 4000-count reverse-contrast LCD. Klein’s manual says it’s built to read in dark or bright light. It runs on 3 AAA batteries and shuts off after about 5 minutes idle. Klein rates calibration as accurate for one year and covers its electrical test tools for two years from purchase.
My call: buy it if you want temperature and amps from one meter without shopping for a probe.
Best for CAT IV 600 V work
Klein Tools CL710 AC/DC digital clamp meter, 600 A
600 A AC/DC1,000 V AC/DC±(2.0% + 8 digits) AC A60 MΩ6,000 µFCAT IV 600 V
Buy it if
You work near the panel and service entrance and want the highest safety rating of the four.
Skip it if
You need temperature readings. The CL710 has no temperature function; the CL390 and Fluke 325 do.
The Klein CL710 has the highest safety rating here, and I’ve used it. It’s sold by Amazon.com, with right-angle test leads, a storage pouch and batteries, per Klein’s datasheet.
Its manual lists CAT IV 600 V and CAT III 1000 V, a 10 on our check. Voltage reads to 1,000 V AC or DC, and Klein says overload protection is 1,000 V on every setting.
AC current runs on 60.00 A and 600.0 A ranges. The low range steps in 0.01 A at ±(2.0% + 8 digits), about ±0.46 A at a 4,500 W element’s 18.75 A, by our math.
It has a low impedance (LoZ) mode, which Klein’s manual says is for identifying and eliminating ghost or stray voltages. None of the other three lists one. Like the CL390, it has a non-contact voltage tester in the jaw, with alerts that grow stronger closer to the voltage source.
Capacitance reaches 6,000 µF, the widest here, and resistance reaches 60 MΩ. Frequency reads from 1 Hz to 500 kHz.
There’s no temperature function; Klein’s datasheet leaves that line blank. That scored a 5 and is the one gap against the CL390.
The display is a 6000-count transflective reverse-contrast LCD, and the dial lights up. The jaw opens 1.4 in. Klein rates it for a 6.6 ft (2 m) drop and IP40.
The manual says it’s for indoor use and shouldn’t be exposed to moisture, rain or snow. At 13 oz (369 g) with batteries, it’s the heaviest of the four. Klein rates calibration as accurate for one year, and the meter shuts off after 5 minutes idle unless you turn that off. Klein’s test tool warranty is two years.
My call: pick it if your calls take you to the panel as often as the water heater.
400 A AC600 V AC/DC±(2% + 5 digits) AC A4,000 Ω30 mm jawCAT III 600 V
Buy it if
You mostly confirm that power is there and a load is drawing current.
Skip it if
You test pump capacitors or need tenths of an amp. The Fluke 325 adds both.
The Fluke 323 is the simplest meter here, and I’ve used it. It’s sold by Amazon.com, with test leads and a soft case.
It reads AC current to 400 A and AC or DC voltage to 600 V, true-rms on both, which the listing says reads linear or non-linear loads accurately, regardless of waveform. Fluke’s page says it’s for verifying load current, AC voltage and the continuity of circuits, switches, fuses and contacts.
The trade-off is its single 400.0 A range. It reads in 0.1 A steps, so the ±(2% + 5 digits) spec comes to about ±0.88 A at 18.75 A, by our math. That scored a 7.
It has no capacitance or temperature function, so both scored a 5. The listing adds that it doesn’t measure DC current.
Resistance reads on 400.0 Ω and 4000 Ω ranges at ±(1% + 5 digits). A 4,500 W, 240 V element’s rated resistance works out to about 12.8 Ω, well inside the low range.
Safety matches the 325: CAT III 600 V and CAT IV 300 V, a 9. The jaw takes a wire up to 30 mm (600 MCM), and continuity beeps at 70 Ω or less.
Fluke says its slim, compact body suits measuring in tight cable compartments. It weighs 265 g, lighter than the 325 or either Klein. A hold button freezes the reading on the display, and Fluke’s page lists test leads, a soft case and a quick reference guide in the box.
There’s no backlight and no Min/Max; Fluke saves those for the 324 and 325. The warranty is two years, the same as the rest of the series.
My call: it’s enough to prove a circuit is live and a load is pulling current. Step to the 325 if you test capacitors.
The four side by side
Tap a column heading on a computer to sort by spec score.
From Fluke’s 320 Series datasheet (4217271A_EN) and Fluke 323 page, Klein’s CL390 and CL710 instruction manuals, Klein’s CL390 product page and CL710 datasheet, read Oct 22, 2026.
What a water heater element should read
A 240 V element’s amps and ohms follow from its wattage. Here’s the arithmetic for the common sizes.
Element
Amps at 240 V
Ohms (rated)
Range it lands in
3,500 W
14.6 A
16.5 Ω
40 A or 60 A range; 400 Ω range
4,500 W
18.75 A
12.8 Ω
40 A or 60 A range; 400 Ω range
5,500 W
22.9 A
10.5 Ω
40 A or 60 A range; 400 Ω range
Our arithmetic: amps = watts ÷ volts; ohms = volts² ÷ watts, at the element’s rated 240 V. Ranges from each maker’s datasheet or manual.
Every element here draws under 40 A, so the low range does the work. On the Fluke 325, CL390 and CL710 that means hundredths of an amp; on the Fluke 323 it means tenths.
Test resistance with the power off. Klein’s manuals say not to measure resistance or continuity on a live circuit. Our guides on 4500 vs 5500 W elements and 240 V vs 208 V elements cover what changes when the voltage or wattage does.
How close each reading is at 18.75 A
Every maker states accuracy as a percent of the reading plus a few counts of the last digit. The last digit is where the meters differ.
Our arithmetic from each maker’s AC current accuracy at 45 to 65 Hz, read Oct 22, 2026. Shorter bar means a tighter reading.
Pick
Range used
Step
Maker’s accuracy
At 18.75 A
Fluke 325
40.00 A
0.01 A
±(2% + 5 digits)
±0.43 A
Klein CL710
60.00 A
0.01 A
±(2.0% + 8 digits)
±0.46 A
Klein CL390
40.00 A
0.01 A
±(2.0% + 9 digits)
±0.47 A
Fluke 323
400.0 A
0.1 A
±(2% + 5 digits)
±0.88 A
Two percent of 18.75 A is 0.375 A on every meter. The digits add the rest: 5 digits at 0.01 A is 0.05 A, but 5 digits at 0.1 A is 0.5 A. That’s why the 323’s spec looks the same on paper and lands twice as wide.
My call: a tenth of an amp rarely changes a diagnosis on a water heater. It matters more on small loads, like a recirculating pump or a control circuit.
Which meter handles which plumbing job
The function each job needs, and which of the four has it, from the makers’ function lists.
Job
Function
Fluke 325
Klein CL390
Klein CL710
Fluke 323
Element drawing current?
AC amps (clamp)
Yes
Yes
Yes
Yes
Element burned open?
Resistance (leads, power off)
Yes
Yes
Yes
Yes
Power at the thermostat?
AC volts
Yes
Yes
Yes
Yes
Well pump run capacitor
Capacitance
Yes
Yes
Yes
No
Pipe or tank temperature
Thermocouple input
No probe in the box
Probe included
No
No
Ghost voltage on a dead wire
LoZ mode
No
No
Yes
No
Wire hot before you touch it
Non-contact voltage
No
Yes
Yes
No
Functions from Fluke’s 320 Series datasheet and Klein’s CL390 and CL710 manuals and datasheet, read Oct 22, 2026. The jobs are my call as a licensed plumber.
For pump work, the capacitance line is the one that splits the field. A well pump control box holds the start parts, and a meter without capacitance can’t check them.
The rating says where in a building’s wiring the meter is built to be used. Higher is closer to the utility.
Rating
Klein’s manual definition
Picks with it
CAT IV
Circuits connected at the source of the building’s low-voltage mains installation
CL710 (600 V); Fluke 325 and 323 (300 V)
CAT III
Circuits connected to the distribution part of the building’s low-voltage mains installation
All four (CL710 to 1000 V; others 600 V)
My call: a 240 V water heater circuit sits on the distribution side, which all four are rated for. The CAT IV numbers matter at the meter base or service entrance.
Klein’s manuals also say to follow local and national safety codes and to use protective equipment against shock and arc blast where live conductors are exposed.
Meters we checked and left out
These came up in Amazon searches on Oct 22, 2026. Here’s what kept each off the list.
Meter
What we found
Why it’s out
Fieldpiece SC260
Compact HVACR clamp meter, sold by a third-party seller
Fieldpiece’s SC260 page wasn’t found, so we couldn’t check specs
Milwaukee 2235-20
400 A clamp meter
Listed with a future ship date, third-party seller
Fluke 902 FC
HVAC clamp meter
Only 6 left from a third-party seller
Klein CL900 and CL910
2000 A AC/DC clamp meters
A bigger class of meter than water heater and pump work needs
AstroAI, KAIWEETS, Luhajoja
Clamp meters from smaller brands
We picked well-documented brands first
How to choose in four questions
Question
If yes
If no
Do you test pump capacitors?
Fluke 325, CL390 or CL710
Fluke 323 can work
Do you need temperature?
CL390 (probe included) or Fluke 325
CL710
Do you work at the service entrance?
CL710 (CAT IV 600 V)
Any of the four
Do you want the fewest settings?
Fluke 323
Fluke 325
My call for a plumber who services electric water heaters and wells: the Fluke 325. For a plumber who also checks recirculating pump lines by temperature, the CL390 saves buying a probe.
If a water heater thermostat is the suspect, our thermostat replacement guide walks through the swap after the meter finds it.
Questions people ask
What is the best clamp meter for plumbers?
The Fluke 325, on our spec score of 9.8. It reads small loads in 0.01 A steps, measures capacitance and temperature, is rated CAT III 600 V and CAT IV 300 V, and has a two-year warranty.
What is a clamp meter?
A meter with a jaw that closes around one wire to read the current in it. Fluke’s listing says the jaw reads current in a conductor without touching or interrupting the circuit. Test leads add voltage, resistance and more.
Multimeter vs clamp meter: which do I need?
A clamp meter reads amps without opening the circuit, and the four here also read volts and ohms through leads. For water heaters and pumps, I’d carry a clamp meter first.
What is a current clamp used for?
Checking that a load is drawing current and how much. On a plumbing call, that’s an element, a well pump or a sump pump, read against its rating.
How many amps should a water heater element draw?
At 240 V, a 3,500 W element draws about 14.6 A, a 4,500 W about 18.75 A and a 5,500 W about 22.9 A. That’s amps = watts ÷ volts.
Can a clamp meter test a water heater element?
Yes, two ways. Clamp one supply wire to read amps with power on, or read the element’s resistance with power off. A 4,500 W, 240 V element is rated at about 12.8 Ω.
How accurate is a clamp meter?
The four here list AC current accuracy of ±(2% + 5 to 9 digits). At 18.75 A that’s about ±0.43 to ±0.47 A on the meters with a 0.01 A step, and ±0.88 A on the Fluke 323.
What is the maximum current a clamp meter can measure?
It depends on the model. The Fluke 323, 325 and Klein CL390 read to 400 A; the Klein CL710 reads to 600 A.
Do I need a true-rms clamp meter?
All four here are true-rms. Fluke’s datasheet says true-rms gives accurate measurements on non-linear signals.
Can a clamp meter test a capacitor?
Three of the four can: the Fluke 325 to 1000 µF, the Klein CL390 to 4,000 µF and the CL710 to 6,000 µF, all through the test leads. The Fluke 323 can’t.
What safety precautions should I take with a clamp meter?
Use a meter rated for where you’re working, never measure resistance or continuity on a live circuit, and use protective equipment where live conductors are exposed, per Klein’s manuals.
CAT III vs CAT IV: what’s the difference?
Per Klein’s manuals, CAT III covers the building’s distribution wiring and CAT IV covers the source of the installation. The CL710 is CAT IV 600 V; the Flukes are CAT IV 300 V.
How we picked these
Why trust me
I’m Isaac Daniels, a licensed journeyman plumber in Georgia (license #JP507711), and I’ve used all four picks. Every spec here comes from Fluke’s and Klein’s datasheets, manuals and product pages, read Oct 22, 2026. Where I add advice of my own, it’s labeled as my call.
How I pick
Only handheld true-rms clamp meters from well-documented brands, sold by Amazon.com, new and in stock, checked through Amazon’s product data the same night.
Facts from each maker’s datasheet or manual first, then its product page.
Each card’s spec score comes from the five checks below. All four score 7.0 or higher.
CPSC recall search for Fluke, Klein Tools, clamp meter and multimeter: no recall of these meters since 2018. Klein’s two recalls in that time cover the NCVT-1 tester and portable power stations.
The spec score, check by check
Each check scores 0 to 10 and counts one fifth. Anything the maker doesn’t list scores a neutral 5. It’s our score from maker documents, not a customer rating or a lab test of our own.
Check (weight)
How it’s scored
Low-amp steps (⅕)
10 for a 0.01 A step on a 40 A or 60 A range; 7 for 0.1 A steps only
Safety rating (⅕)
10 for CAT IV 600 V; 9 for CAT IV 300 V with CAT III 600 V; 8 for CAT III 600 V only
Capacitance (⅕)
10 when it measures to 1,000 µF or more; 5 when there’s no capacitance function
Temperature (⅕)
10 for a thermocouple temperature input; 5 when there’s none
Warranty (⅕)
10 for two years in writing; 8 for one year; 5 when none is stated
Total
Average of the checks, to one decimal
Pick
Low-amp steps
Safety
Capacitance
Temperature
Warranty
Score
Fluke 325
10 (0.01 A)
9 (CAT IV 300 V)
10 (1000 µF)
10 (14 to 752°F)
10 (2 yr)
9.8
Klein CL390
10 (0.01 A)
8 (CAT III 600 V)
10 (4,000 µF)
10 (−40 to 1,832°F)
10 (2 yr)
9.6
Klein CL710
10 (0.01 A)
10 (CAT IV 600 V)
10 (6,000 µF)
5 (none)
10 (2 yr)
9.0
Fluke 323
7 (0.1 A)
9 (CAT IV 300 V)
5 (none)
5 (none)
10 (2 yr)
7.2
Sources
Fluke Corporation, 320 Series True-rms Clamp Meters datasheet (4217271A_EN, 5/2012) and Fluke 323 product page: read Oct 22, 2026.
Klein Tools, CL390 instruction manual (retailer-hosted copy) and CL390 product page: read Oct 22, 2026.
Klein Tools, CL710 instructions (0225, retailer-hosted copy) and CL710 datasheet: read Oct 22, 2026.
Klein Tools, warranty by product group (Electrical Test and Measurement Tools): read Oct 22, 2026.
Brand-written Amazon listing text for B00AQKIEXY, B0091EXB2A, B08DTDCG7T and B0DQ6CFRGH: read through Amazon’s product data, Oct 22, 2026.
Amazon listings for the picks and the left-out meters (titles, seller, condition, stock): read through Amazon’s product data, Oct 22, 2026.
U.S. Consumer Product Safety Commission recall data, searched for Fluke, Klein Tools, clamp meter and multimeter: Oct 22, 2026.
Google results for “clamp meter”: seen Oct 22, 2026. Search volumes from Semrush, Oct 22, 2026.
