How to Use a Clamp Meter: AC and DC Steps, Clamp Meter vs Multimeter, Leakage Current and 25 Japanese Models Compared

Quick answer: how to use a clamp meter

  • Set the dial to A AC (or A DC for batteries, solar and vehicles). Keep the test probes out of the jacks while you measure current (Fluke).
  • DC only: zero the meter with the jaws closed and empty before every reading. Hall-effect sensors pick up the Earth's magnetic field and nearby magnets, so the display drifts until you zero it (Fluke; HIOKI also says to zero before DC).
  • Clamp around one conductor only. Hot and neutral together cancel each other and read close to zero (HIOKI, Fluke, EEVblog). A line splitter separates the wires of a power cord.
  • Close the jaws fully and center the wire on the alignment marks; an off-center wire or a gap in the jaws reads low (HIOKI, Fluke).
  • Read, then range up if the display shows an over-range warning (Jonard). For small currents, loop the wire through the jaws N times and divide the reading by N (EEVblog).
  • Leakage is the exception: a leakage clamp meter is clamped around hot and neutral together on purpose, so the tiny difference that flows to ground is what shows (HIOKI, Fluke).

This guide explains how a clamp meter (amp clamp) works, how to measure AC and DC current step by step, when a clamp meter beats a multimeter and when it does not, how leakage current is measured, and which of the Japanese HIOKI and KYORITSU clamp meters we stock fits which job. The procedure comes from the makers' own guides (Fluke, HIOKI), two trade-school and tool-maker tutorials (UTI, Jonard) and real questions from the EEVblog forum. Sources are at the end.

Safety note: this is a general guide, not training. Check the measurement category (CAT rating) of your meter against the circuit, follow your local code and the instruction manual, and never touch anything on the jaw side of the barrier while measuring (HIOKI).

What a clamp meter measures, and how

Fluke sums it up in six words: "Clamps measure current. Probes measure voltage." A clamp meter is a basic digital multimeter with a current sensor built into a hinged jaw. Clamp the jaw around a wire and the meter reads the current without cutting the circuit or switching it off (Fluke). The jaws are ferrite iron under the plastic; they concentrate the magnetic field that the current produces (Fluke).

There are two sensing methods, and the difference decides whether a meter can read DC:

  • Current transformer (CT) clamps measure AC only. The wire inside the jaws is a one-turn primary; coils wound on the jaws are the secondary. Fluke's example: with 1,000 secondary turns, 1 A in the wire gives 1 mA at the meter input. Fluke states that "current transformer clamp meters only respond to ac waveforms" (Fluke, Inside CT clamp meters). The HIOKI 3280-10F, CM3289, CM3291 and CM4141 and the KYORITSU KEW 2200/2117R/2127R/2204R in our table are AC-only meters.
  • Hall-effect clamps measure AC and DC. The jaws are not wound with wire; a small air gap at the jaw tips holds a semiconductor Hall sensor that outputs a voltage proportional to the magnetic flux. Fluke says these meters "can measure both ac and dc current up to the kilohertz (1000 Hz) range." Because the core also concentrates DC fields, including the Earth's, a Hall-effect clamp must be zeroed before a DC reading (Fluke, Inside Hall Effect clamp meters). The HIOKI 3287, 3288, CM4371/CM4373/CM4375 and the KYORITSU 2010, 2300R and KEW 2009R are AC/DC meters.

A third type uses a flexible Rogowski coil instead of rigid jaws. Fluke lists it as AC-only; in our experience its use is thick or bundled cables and panels where rigid jaws do not fit. The HIOKI 3280-70F ships with a CT6280 flexible sensor, and the KYORITSU KEW 2210R is a flexible-sensor meter rated to 3,000 A with a 150 mm loop (product pages).

Clamp meter vs multimeter: which one for which job

Fluke's own comparison puts it plainly: a digital multimeter is "essentially a voltage-measuring tool with some current abilities," and a clamp meter is "basically a current-measuring tool with some voltage abilities." The practical differences from that article and from Fluke's clamp-meter overview:

  Clamp meter Digital multimeter
How current is measured Around the wire, circuit stays live and uncut (Fluke) In series: the circuit must be opened and the meter inserted (HIOKI)
Current range Typically 0 to 100 A minimum, many to 600 A, 999 A or 1,400 A; flexible probes to 2,500 A (Fluke) Direct measurement usually under 20 A; Fluke says a DMM cannot measure 10 A for more than 30 seconds without risking damage
Resolution Nearest tenth or hundredth of a unit, which Fluke calls sufficient for electrical work Milli-units (mV, mA, mΩ) for electronics (Fluke)
Voltage, resistance, continuity Most clamp meters include them via probes (Fluke); 16 of the 21 load-current meters in our table below list voltage ranges Core functions, with more ranges
Best for Service, installation and maintenance of electrical systems and HVAC (Fluke); inrush and Min/Max functions on many models (Fluke) Work that needs milli-unit resolution, such as electronics (our reading of Fluke's comparison)

Fluke's conclusion is that one DMM plus one clamp meter is a cost-effective pairing, and that electricians often find the clamp meter the more versatile single tool. A forum member on EEVblog's test-gear board made the same point from the shop floor: for current, a clamp is "way safer and faster than bodging a DMM in circuit" (beanflying, Oct 2021).

How to measure AC current with a clamp meter, step by step

The order below follows Fluke's "How to measure current with a clamp meter" page and HIOKI's "How to Use Clamp Meters" page; where a step is our own practice, it says so.

  1. Inspect the meter. Fluke's safety checklist: look for cracks or missing plastic on the case, damaged insulation on the probes, and replace the battery at the low-battery indicator "to avoid false readings."
  2. Remove the test probes from the jacks. Fluke: "Never measure current while the test probes are inserted into the input jacks." Keep your fingers behind the tactile barrier (Fluke).
  3. Turn the dial to A AC. If the meter has manual ranges, our practice is to start on the highest range and step down. Auto-ranging meters such as the HIOKI CM3289 and KYORITSU KEW 2117R choose the range for you (product pages).
  4. Isolate one conductor. This is the step beginners miss. HIOKI: load-current clamp meters "can only be clamped around one wire." UTI explains why: clamping around a whole cord with both hot and neutral "cancels the magnetic field, giving you a false zero reading." On a power cord, use a line splitter (see FAQ) or open the panel and clamp the hot conductor alone.
  5. Open the jaws with the lever, put the wire inside, and let the jaws close fully. HIOKI: position the wire in the center of the clamp for maximum accuracy. Fluke: center it on the alignment marks. Fluke's leakage guide adds that jaw faces must be clean and closed with no air gap, and that you should not twist the jaws.
  6. Read the display. Let the reading stabilize before noting it (UTI). If an over-range warning appears, move to a higher range (Jonard); HIOKI's 3280-10F and CM3291 pages list an "over-input warning (OF)" for this.
  7. Small currents: multiply, then divide. On EEVblog's test-gear board (Oct 2021), SilverSolder's tip for currents below the meter's resolution is to "loop the wire carrying the current a couple of times through the clamp." The reading is multiplied by the number of turns, so true current = reading ÷ turns. A line splitter's x10 slot does the same thing with ten built-in turns (x10 slot: Extech 480172 datasheet; ten turns: David Hess on EEVblog).
  8. Remove the clamp and power the meter off (Jonard). HIOKI warns that leaving a clamp-on power meter connected after use can let an excessive current damage the sensor.

Measuring DC current: the extra step

Set the dial to A DC, then press the Zero button with the jaws closed and empty before you clamp the wire (Fluke). UTI's tutorial says to zero before each measurement and to hold the clamp steady while reading. Fluke's Zero button also removes the DC offset from the display. On the HIOKI 3287/3288 and CM4371–CM4375 pages this appears as "zero adjust" in the function list.

What the spec means for the job: a meter listed as "AC" or "Average Value Rectification (MEAN), AC" cannot read battery, solar or vehicle current at all, because a CT responds only to AC (Fluke). If your work includes a 12 V/48 V system, an inverter's DC side, or an EV charger's DC output, you need one of the AC/DC models.

Measuring voltage with a clamp meter

Insert the probes into the jacks named in your manual (COM for black, V/Ω for red on most meters), set the dial to V AC or V DC, and place the black probe on neutral or ground and the red probe on the live conductor (Jonard). Fluke's safety list: connect the common probe first and disconnect the live probe first. Most load-current meters in our table list AC and DC voltage to 600 V (HIOKI 3280/3287/3288/CM3289/CM3291, KYORITSU KEW 2200/2200R/2117R/2127R) or 1,000 V (HIOKI CM4141/CM4371/CM4373/CM4375, KYORITSU KEW 2009R; the 2009R lists 750 V AC). The KEW 2204R, 2210R, 2300R and 2010 pages list current only (product pages).

True RMS or average responding: when it matters

A clamp meter's detection method is one of the first lines on every HIOKI and KYORITSU product page: "True RMS Rectification" or "Average Value Rectification (MEAN)." Both read the same on a clean sine wave. On distorted current, Fluke states that an averaging meter can read "up to 40% low or 10% high," and HIOKI says "distortion of the waveform causes the values to diverge," and HIOKI recommends a true RMS meter when you need true RMS readings. Fluke names the usual sources of distortion: variable-speed drives, computers, electronic ballasts and HVAC equipment.

What that means on site: if you measure motor circuits on a VFD, LED lighting, office floors full of switch-mode power supplies, or anything with an inverter, choose a true RMS meter. If you mainly check heaters, incandescent lighting or transformer feeds at 50/60 Hz, an average-responding meter reads correctly. In the table below, the HIOKI 3280-10F, 3280-70F and 3288 and the KYORITSU KEW 2200, 2010 and 2413F are MEAN meters; the KEW 2127R page says "RMS" only; the rest are true RMS.

How to measure leakage current with a clamp meter

Leakage measurement turns the "one conductor only" rule around. HIOKI: when measuring leakage current, two wires may be clamped simultaneously. The method, from Fluke's leakage-measurement guide and HIOKI's page:

  • Single-phase: clamp hot and neutral together. The two currents cancel except for what leaves the circuit through insulation and goes to ground; that remainder is the reading (Fluke, HIOKI).
  • Three-phase: clamp all three phases, plus the neutral if there is one (Fluke).
  • Ground wire alone: measures the total leakage returning through the intended ground path (Fluke). HIOKI says ground wires should be measured alone.
  • Hot + neutral + ground together: whatever is left is flowing through an unintended path, such as a panel bonded to a water pipe (Fluke).
  • Trace it: measure the main feed first, then each branch; switch the load off to separate wiring leakage from equipment leakage (Fluke).

Why a normal clamp meter cannot do this: Fluke says most clamp meters simply will not register the currents below 5 mA that leakage clamps are built for. HIOKI puts typical leakage at "several tens of μA if many loads are connected," and Fluke says that on a loaded circuit it "could well be in the order of milliamps." A leakage clamp meter resolves 0.01 mA or finer: the HIOKI CM4001 lists a 60.00 mA lowest range (0.01 mA step), the CM4002 and CM4003 list 6.000 mA (0.001 mA step), and the KYORITSU KEW 2433RBT lists a minimum resolution of 0.01 mA (product pages).

What the spec means for the job: nuisance GFCI/RCD trips are the usual reason an electrician buys a leakage clamp (Fluke notes that accumulated leakage can cause unnecessary, intermittent tripping). The HIOKI CM4002/CM4003 list a low-pass filter with a 180 Hz cutoff; Fluke's guide explains that electronic loads add harmonics to leakage and that a filter isolates the 50/60 Hz component. The CM4001 at 115 g and 37 mm wide fits a crowded panel; the CM4002/CM4003 at 400 g has a 40 mm jaw for feeder cables (product pages).

Japanese clamp meters compared

Specs are copied from each product page. Two columns are calculated by us, with the formula shown:

HIOKI CM3289 AC clamp meter HIOKI CM3289 AC Clamp Meter, True RMS, 1000 A, Slim Jaw HIOKI CM3291 AC Clamp Meter HIOKI CM3291 AC Clamp Meter
  • Smallest step on the lowest current range: the last digit of the lowest range as the product page writes it (42.00 A = 0.01 A steps; 100.0 A = 0.1 A steps), or the page's stated minimum resolution. This tells you the finest current you can read, not the accuracy.
  • Smallest step as a share of a 1 A load: step ÷ 1 A × 100. A 0.01 A step is 1% of a 1 A load; a 0.1 A step is 10%, which is coarse for small motors or lighting circuits.
Model AC / DC Detection Max current Jaw (mm) Smallest step (lowest range) Step ÷ 1 A Notable (product page) Weight / origin
HIOKI CM3289 AC True RMS 1,000 A 33 0.01 A (42.00 A range) 1% 16 mm thin body, CAT IV 300 V / CAT III 600 V, 1 m drop, −25 to 65 °C, CT6280 flexible sensor optional approx. 100 g, Japan
HIOKI CM3291 AC True RMS 2,000 A 46 0.01 A (42.00 A range) 1% Same 16 mm body with a larger jaw; flexible sensor function 100 g, Japan
HIOKI 3280-10F AC MEAN 1,000 A 33 0.01 A (42.00 A range) 1% Drop-proof, auto-ranging, CAT IV 300 V / CAT III 600 V 100 g, Japan
HIOKI 3280-70F set AC MEAN 1,000 A 33 (jaw); flexible sensor included 0.01 A (42.00 A range) 1% 3280-10F plus CT6280 flexible current sensor and case 100 g (meter), Japan
HIOKI 3287 AC/DC True RMS 100 A 35 0.01 A (10.00 A range) 1% Low-current AC/DC model, zero adjust, CAT III 600 V 170 g, Japan
HIOKI 3288 AC/DC MEAN 1,000 A 35 0.1 A (100.0 A range) 10% Zero adjust, CAT III 600 V 150 g, Japan
HIOKI 3288-20 AC/DC True RMS 1,000 A 35 0.1 A (100.0 A range) 10% True RMS version of the 3288 150 g, Japan
HIOKI CM4141-50 / CM4141-90 AC True RMS 2,000 A 55 Not confirmed (lowest range not listed) — 1,000 V ranges, capacitance, frequency, temperature, low-pass filter; -90 adds the Z3210 wireless adapter 300 g (-90), Japan
HIOKI CM4371-50 / CM4371-90 AC/DC True RMS 600 A 33 Not confirmed — IP54, auto AC/DC detection, DC power, voltage detection, zero adjust 340 g, Japan
HIOKI CM4373-50 / CM4373-90 AC/DC True RMS 2,000 A 55 Not confirmed — IP54, 1,000 V ranges, 55 mm jaw for large feeders 530 g, Japan
HIOKI CM4375-50 / CM4375-90 AC/DC True RMS 1,000 A AC / 999.9 A DC 34 Not confirmed — IP54, DC power range to 1,000 kVA, 1,000 V ranges 350 g (-90), Japan
KYORITSU KEW 2200 AC MEAN 1,000 A 33 Not confirmed (4,199 counts; ranges not listed) — 350 h battery life, 600 V ranges 120 g, Thailand
KYORITSU KEW 2200R AC True RMS 1,000 A Not confirmed 0.01 A (stated minimum resolution) 1% IEC 61010-2-032, CAT IV 300 V / CAT III 600 V 120 g, Thailand
KYORITSU KEW 2117R AC True RMS 1,000 A 33 0.01 A (60.00 A range) 1% NCV LED listed, approx. 170 h battery, auto range 220 g, Thailand
KYORITSU KEW 2127R AC RMS 1,000 A Not confirmed Not confirmed — 600 V ranges, 40 MΩ 220 g, Japan
KYORITSU KEW 2204R AC True RMS 400 A 90 0.001 A (stated minimum resolution) 0.1% 90 mm jaw, CAT IV 600 V / CAT III 1,000 V, max/min 200 g, Taiwan
KYORITSU KEW 2210R AC (flexible) True RMS 3,000 A 150 (loop) 0.01 A (30.00 A range) 1% Flexible sensor, 150 mm maximum conductor diameter 300 g, Taiwan
KYORITSU 2300R AC/DC True RMS 100 A 10 (open fork) Not confirmed (1,049 counts) — Fork-type sensor, 10 mm conductor; our use: single wires in tight bundles 110 g, Thailand
KYORITSU KEW 2009R AC/DC True RMS 2,000 A 55 Not confirmed (1,999 counts) — 1,000 V DC / 750 V AC, 55 mm jaw 540 g, Thailand
KYORITSU 2010 AC/DC MEAN 20 A 7.5 Not confirmed (2,000 counts) — Separate sensor (23 × 18 × 153 mm) for 20 A AC/DC 220 g, Japan
KYORITSU KEW 2500 DC mA — 100 mA (range to 120.0 mA) 6 0.01 mA (stated range 0.01 to 120.0 mA) 0.001% Accuracy ±0.2% rdg ±5 dgt below 21.49 mA; our use: 4–20 mA loops 290 g, Japan
HIOKI CM4001 / CM4001-90 AC leakage True RMS 600 A 24 0.01 mA (60.00 mA range) 0.001% Inrush, peak, comparator, event function; 37 mm wide 115 g, Japan
HIOKI CM4002 / CM4002-90 AC leakage True RMS 200 A 40 0.001 mA (6.000 mA range) 0.0001% 15 Hz–2 kHz, 180 Hz low-pass filter, CAT IV 300 V / CAT III 600 V 400 g, Japan
HIOKI CM4003 / CM4003-90 AC leakage True RMS 200 A 40 0.001 mA (6.000 mA range) 0.0001% CM4002 plus RMS and waveform output, optional AC adapter 400 g; origin Not confirmed (-90: Japan)
KYORITSU KEW 2433RBT AC leakage + load True RMS 400 A Not confirmed 0.01 mA (40 mA range) 0.001% Bluetooth enabled, 40 mA / 400 mA / 400 A ranges, peak hold 270 g, Japan
KYORITSU KEW 2413F AC leakage + load MEAN 1,000 A (page lists this under DC current; Not confirmed) Not confirmed ("large-diameter") 0.1 mA (stated minimum resolution) 0.01% Recorder output, peak hold 570 g, Japan

Reading the table: the 100 g HIOKI CM3289 and 3280-10F and the 120 g KYORITSU KEW 2200/2200R all read in 0.01 A steps on a 33 mm jaw (KEW 2200R jaw and KEW 2200 lowest range not confirmed), so the choice between them is true RMS or MEAN; the CM3291 is the same HIOKI body with a 46 mm jaw. Meters that list only 0.1 A steps (HIOKI 3288/3288-20) trade resolution for 1,000 A AC/DC capacity. For panels with 55 mm feeders you are choosing between the HIOKI CM4141 (AC), CM4373 (AC/DC) and KYORITSU KEW 2009R (AC/DC).

What to check before buying: these are Japanese-market models. The HIOKI pages list EN 61010 and CAT ratings; the KYORITSU KEW 2200R and 2204R pages list IEC 61010-1 and IEC 61010-2-032. UL or CSA listing is Not confirmed for all models, and the manual language in the box is Not confirmed. We do not claim these meters are more accurate than other brands; we have not found a test that compares them.

Which clamp meter for which job

Everyday service and panel work (AC, in a shirt pocket)

  • HIOKI CM3289: true RMS, 1,000 A, 16 mm thick and about 100 g, CAT IV 300 V. The thin sensor is HIOKI's answer to crowded panels (product page).
  • KYORITSU KEW 2117R: true RMS, 60.00 A lowest range, NCV LED listed on the product page.
  • HIOKI 3280-10F or KEW 2200: the MEAN versions for 50/60 Hz loads without inverters.

Batteries, solar, vehicles and inverter DC sides (AC/DC)

  • HIOKI 3287: 10.00 A lowest range in 0.01 A steps, for small DC loads.
  • HIOKI 3288-20: 1,000 A AC/DC, true RMS, still 150 g.
  • HIOKI CM4371-50: 600 A AC/DC with IP54, auto AC/DC detection and 1,000 V ranges, for outdoor and solar work.

Large feeders and busbars

Nuisance GFCI/RCD trips and insulation checks (leakage)

  • HIOKI CM4001: 0.01 mA steps, 115 g, 24 mm jaw for branch circuits.
  • HIOKI CM4002: 0.001 mA steps, 40 mm jaw, 180 Hz filter for harmonic-rich loads.
  • KYORITSU KEW 2433RBT: leakage and load current in one, Bluetooth enabled.

Instrumentation loops and tightly packed wiring

HIOKI CM3289 AC clamp meter true RMS 1000 AEveryday AC, pocket sizeHIOKI CM3289

True RMS, 1,000 A, 16 mm thin, CAT IV 300 V.

View CM3289
KYORITSU KEW 2117R AC clamp meterAC with NCVKYORITSU KEW 2117R

True RMS, 60/600/1,000 A, NCV LED listed.

View KEW 2117R
HIOKI 3288-20 AC/DC clamp meterAC/DC, 150 gHIOKI 3288-20

1,000 A AC/DC, true RMS, zero adjust.

View 3288-20
HIOKI CM4371-50 AC/DC clamp meter IP54AC/DC, IP54HIOKI CM4371-50

600 A, 1,000 V, auto AC/DC detection.

View CM4371-50
KYORITSU KEW 2210R flexible clamp meter 3000 AFlexible, 3,000 AKYORITSU KEW 2210R

150 mm loop for busbars and bundles.

View KEW 2210R
HIOKI CM4001 AC leakage clamp meterLeakage, 0.01 mAHIOKI CM4001

60 mA to 600 A, 115 g, 24 mm jaw.

View CM4001

FAQ: questions people actually ask

My clamp meter reads zero on a live appliance cord. Why?

That was the exact question that opened an EEVblog beginners thread in September 2021: a UT204+ on the 60 A AC range around a power cord showed nothing. The first reply (RoGeorge): "Clamp around only a single wire, not around a cable containing 2-3 wires." UTI puts it this way: clamping a whole cord with hot and neutral "cancels the magnetic field, giving you a false zero reading." Another reply (ledtester) suggested an AC line splitter, which separates the conductors of a cord so you can clamp one.

What does the x10 slot on a line splitter do?

The Extech 480172 datasheet lists "x1 for direct readings" and "x10 for actual reading multiplied by 10." The x10 path loops the conductor ten times through the clamp window, so the meter sees ten times the field; divide the display by 10 for the true current. David Hess explained the same thing about the Fluke/Amprobe ELS2A in the EEVblog beginners thread: "the extra clamp position has 10 turns for 10 times sensitivity." The Extech 480172 is rated to 15 A (datasheet).

Can I use a clamp meter to measure DC current from a battery or solar panel?

Only with a Hall-effect (AC/DC) clamp meter; a current-transformer clamp responds only to AC (Fluke). Zero the meter with the jaws closed and empty first, and hold it still while reading (Fluke, UTI). In our table the AC/DC models are the HIOKI 3287, 3288, 3288-20, CM4371, CM4373 and CM4375, and the KYORITSU 2010, 2300R and KEW 2009R.

Is a clamp meter better than a multimeter?

They answer different questions. Fluke: a DMM is a voltage tool with some current ability, and a clamp meter is a current tool with some voltage ability; a DMM gives milli-unit resolution, a clamp meter reads to the tenth or hundredth. For electrical work Fluke suggests owning one of each. If you only buy one for service calls, most clamp meters in our table also measure AC/DC voltage and resistance, and the HIOKI load-current models list continuity (product pages).

Why does my average-responding meter disagree with a true RMS meter?

Because the current is not a clean sine wave. Fluke states averaging meters can read up to 40% low or 10% high on distorted waveforms from drives, computers, ballasts and HVAC. HIOKI says the two methods agree on an undistorted sine wave and diverge as distortion grows, and recommends a true RMS meter when you need true RMS readings.

How do I measure leakage current to find a tripping GFCI?

Use a leakage clamp meter, clamp hot and neutral together (all phases plus neutral on three-phase), and read the difference. Measure the main feed first, then each branch, and switch loads off to separate wiring leakage from equipment leakage (Fluke). Fluke notes most standard clamp meters will not register currents below 5 mA, which is why a dedicated leakage meter with 0.01 mA or finer resolution is needed.

How accurate is a clamp meter?

It depends on the model and range. The HIOKI CM3289 page lists a basic AC current accuracy of ±1.5% rdg ±5 dgt; the KYORITSU KEW 2500 lists ±0.2% rdg ±5 dgt below 21.49 mA. HIOKI adds that positioning the wire in the center of the jaws is needed for maximum accuracy, and Fluke's leakage guide says dirty or incompletely closed jaw faces reduce accuracy. Where a product page does not state accuracy, we mark it Not confirmed rather than guess.

Related guides

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Sources

Last reviewed: October 2026. Not affiliated with Fluke, HIOKI, KYORITSU, Extech, UTI or Jonard.

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