Hioki CM4002 AC Leakage Clamp Meter — Find Nuisance RCD Trips Down to 0.001 mA

The fault that never happens while you’re standing there

Every sparky knows the job. The safety switch on the shop’s power circuit drops out twice a week, always after hours, never when you’re on site. You reset it, test it with an RCD tester, everything passes, and you leave. Two days later the phone rings again.

Intermittent earth leakage is one of the most expensive faults in Australian electrical work, because the cost isn’t in the repair — it’s in the return visits, the lost stock in a cold room, the production line that stopped, and the customer who starts to wonder whether you actually know what you’re doing.

The reason it’s so hard to pin down is simple physics. Under AS/NZS 3000, RCD protection is now standard across most final subcircuits, and a 30 mA device is permitted to operate anywhere between 50% and 100% of its rated residual current. That means a board sitting at 18 mA of standing leakage isn’t faulty — it’s just one kettle, one damp motor winding, or one extra inverter away from tripping. A pass/fail RCD tester will never show you that. You need to see the actual number, and you need to see it while the plant is running.

That’s exactly the job the Hioki CM4002 AC Leakage Clamp Meter was built for.

What the CM4002 actually does

The CM4002 is a dedicated true-RMS earth leakage clamp meter. Instead of measuring current in one conductor, you clamp all the live conductors of a circuit together — active and neutral on a single-phase final subcircuit, or all three phases plus neutral on a 415 V feeder. Under healthy conditions those currents cancel, and the meter reads close to zero. Whatever’s left over is the vector sum: current that has found a path back to earth. That’s the zero-phase current, and it’s the same quantity the RCD upstream is watching.

Six ranges span 6.000 mA, 60.00 mA, 600.0 mA, 6.000 A, 60.00 A and 200.0 A, with a defined accuracy range from 0.060 mA to 200.0 A. The bottom range resolves to 0.001 mA. That span matters more than it looks: the same instrument that resolves a microamp-level insulation problem in a control cabinet can also read the 80 A load current on the feeder beside it, so you’re not swapping tools mid-diagnosis.

Basic accuracy is ±1.0% rdg ±5 dgt from 45 Hz to 400 Hz across the 6.000 mA to 6.000 A ranges — comfortably inside the band where a 50 Hz Australian installation lives.

Readings you can defend, backed by IEC/EN 61557-13

Any clamp will show you a number. The question is whether that number survives scrutiny when you put it in a report.

Hioki designed the CM4002’s current transformer specifically to answer that. The core and shielding are built from high-permeability magnetic materials and the CT is wound with a uniform coil, and the instrument complies with IEC/EN 61557-13 Class 2, 30 A/m — the international performance standard written specifically for leakage clamp meters. Three practical consequences follow:

Position inside the jaw stops mattering. Sensitivity is uniform across the aperture, so a fat two-core bundle jammed against one side of the jaw reads the same as one perfectly centred. In a densely wired distribution board, “perfectly centred” is a fantasy.

Neighbouring busbars stop lying to you. Shielding blocks external magnetic fields, with the effect of a 400 A/m external field at 50/60 Hz specified at 4 mA or less. When you’re clamping a 15 mA leakage path 50 mm away from a loaded 415 V busbar, that specification is the difference between a diagnosis and a guess.

Inverter noise can be filtered out. A switchable low-pass filter with a −3 dB point at 180 Hz ±30 Hz strips high-frequency capacitive leakage from variable speed drives, solar inverters and switch-mode supplies. This is the feature that quietly earns its keep on modern sites. The EMC filters inside a VSD or a PV inverter dump genuine — but harmless — high-frequency current to earth. An unfiltered clamp adds all of it to the reading and sends you hunting a fault that doesn’t exist. With the filter on, the CM4002 sees the installation roughly the way a Type AC or Type A RCD sees it: at power frequency, where tripping decisions are actually made.

Ø40 mm jaw, built for real switchboards

The jaw opens to a Ø40 mm conductor diameter with jaw dimensions of 75 mm × 20 mm. That’s enough to take a three-phase-plus-neutral bundle on a submain, a large single cable, or several smaller circuits at once when you’re bisecting an installation to isolate the offending branch. Undersized jaws are the most common reason a leakage clamp ends up unused in the back of a ute — this one goes where the work is.

Catching the fault that only happens at 3am

This is where the CM4002 separates itself from a basic leakage clamp.

Fit the optional Z3210 Wireless Adapter and the meter gains Bluetooth®, connecting to Hioki’s free GENNECT Cross app on a phone or tablet. Two workflows open up:

Event recording. Set a leakage threshold and a recording window, clamp the meter onto the suspect circuit, and walk away. The instrument logs trip start times, trip stop times and maximum current values to internal memory — up to 999 events, over a recording period of up to 30 days (battery life permitting). You don’t need to stay connected to the tablet while it records. Come back, pull the data into GENNECT Cross, and you have a timestamped picture of an intermittent fault that no amount of standing in front of a switchboard would ever have given you.

Photo drawing for routine inspections. Photograph the board, then tap measurement locations on the image and drop the live readings onto the photo. Work upstream to downstream, and the fault location builds itself visually as you go. You can export a PDF report on site, before you’ve left the customer’s car park — which does more for repeat work than any amount of marketing.

With the Z3210 fitted, GENNECT Cross will also display current harmonics up to the 30th order, along with content factor and total harmonic distortion — useful context when leakage and power quality problems are tangled together on the same site.

Prefer to leave the phone in your pocket? The Excel® Direct Input function types measured values straight into a spreadsheet on a connected device each time auto-hold captures a reading. For calibration technicians and facilities teams doing scheduled runs across dozens of circuits, that’s an entire transcription step — and an entire class of transcription error — deleted.

The details that matter on a long day

• Dual readout shows current and frequency simultaneously, so you can spot straight away when a reading is dominated by something other than 50 Hz.
• Auto hold waits for the value to stabilise, then locks it — for when the meter is at arm’s length inside a board and the display isn’t.
• Comparator gives audible and visual pass/fail against a threshold you set. Eyes stay on the work, not the screen.
• Max / Min / AVG / PEAK MAX / PEAK MIN capture, plus inrush current measurement for motor and transformer starts.
• 48 hours of continuous running on two AA alkalines (about 30 hours with the Z3210 fitted and communicating). Batteries you can buy at any servo in the country.
• −10°C to 65°C operating range — a roof cavity in a Mildura February, or a cool store in a Tasmanian winter.
• 400 g and 233 mm long, with the C0203 carrying case included.

Where it earns its keep in Australia

Electrical contractors tracing nuisance safety switch trips in retail, hospitality and residential switchboards — measuring standing leakage before it becomes a callback, and quantifying how close a board is running to its 30 mA limit.

Industrial maintenance teams on VSD-heavy plant, where the filter function separates genuine insulation degradation from the capacitive leakage that drives are supposed to produce.

Solar installers verifying leakage behaviour on grid-connected PV systems, where inverter EMC filters, long DC runs and damp roof penetrations all contribute earth current — and where the difference between a real AS/NZS 5033 insulation problem and normal system leakage needs to be established quickly.

Facility managers and safety officers building a documented leakage baseline across a site, so that next year’s figures mean something. Earth leakage current measurement is also used in in-service testing work under AS/NZS 3760 alongside insulation resistance testing, particularly on equipment where a standard insulation test isn’t appropriate.

TAFEs, RTOs and engineering departments teaching residual current theory with an instrument that demonstrates the concept properly — including why jaw position and external fields matter, using a meter engineered to defeat both.

Choosing between the CM4002, CM4003 and CM4001

The CM4002 and CM4003 share the same sensor, the same six ranges and the same IEC/EN 61557-13 Class 2 compliance. The differences are about where you work:

• CM4002 carries the higher safety rating — CAT IV 300 V and CAT III 600 V conductor-to-ground. If you work at the origin of an installation, at the main switchboard, or on service and metering equipment, this is the model to specify.
• CM4003 trades safety category down to CAT III 300 V but adds an analogue output (RMS and waveform) for feeding a recorder or Memory HiCorder, plus external DC power for unattended recording that outlasts a set of batteries.
• CM4001 is the entry point in the family, with a lower event memory capacity.

For general field work in Australian installations — where a 415 V three-phase system sits at roughly 240 V phase-to-earth, and where you’re regularly working upstream of the main switch — the CM4002’s CAT IV 300 V rating is the sensible default. As always, confirm the measurement category against your own risk assessment and the specific point of the installation you’re working on.

Ready to test out of the box

Every CM4002 ships with the C0203 carrying case, instruction manual, operating precautions and two AA alkaline batteries. Order the CM4002-90 if you want the Z3210 Wireless Adapter bundled from day one — for anyone doing intermittent fault work, it’s the version to get.

We’re a specialist test and measurement supplier, not a general tool shop. That means we can talk you through whether the CM4002 or the CM4003 fits your work, sort out calibration and recertification when it’s due, and keep you supplied with the accessories that actually get used. Got a leakage problem you can’t pin down? Talk to us before you order — we’d rather sell you the right instrument once.

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Technical Specifications

Specifications sourced from Hioki CM4002/CM4003 catalogue (rev. CM4002_CM4003E6-3ZE) and the Hioki global product page. Specifications subject to change by the manufacturer.

What is the Hioki CM4002 used for? The Hioki CM4002 is an AC leakage clamp meter used to measure earth leakage current in electrical installations without disconnecting conductors. Electricians clamp it around all live conductors of a circuit at once — active and neutral, or three phases plus neutral — and the meter reads the residual current returning to earth. Its main applications are diagnosing nuisance RCD and safety switch trips, establishing standing leakage baselines during routine inspections, and locating insulation faults in industrial and solar installations.

How does the Hioki CM4002 find the cause of a tripping safety switch? It measures the actual leakage current the RCD is responding to, in milliamps, while the installation stays energised. Because an RCD may operate anywhere between 50% and 100% of its rated residual current, a 30 mA safety switch can trip on as little as 15 mA of accumulated leakage. By clamping progressively downstream through a switchboard, an electrician narrows the leakage to a single final subcircuit. With the optional Z3210 adapter fitted, the CM4002 can also log up to 999 trip events over as long as 30 days, capturing faults that only appear overnight or under specific load conditions.

What is the lowest current the Hioki CM4002 can measure? The CM4002 has a defined accuracy range starting at 0.060 mA, with a best resolution of 0.001 mA on the 6.000 mA range. Its full span extends to 200.0 A across six ranges, so it covers both micro-level leakage detection and ordinary load current measurement.

Is the Hioki CM4002 compliant with IEC 61557-13? Yes. The CM4002 complies with IEC/EN 61557-13 at Class 2, 30 A/m — the international performance standard specifically for leakage current clamp meters. The instrument is also designed to EN 61010 for safety (as a type A current sensor) and EN 61326 for EMC.

What is the difference between the Hioki CM4002 and the CM4003? Both share the same sensor, six ranges and IEC/EN 61557-13 Class 2 compliance. The CM4002 has the higher safety rating at CAT IV 300 V / CAT III 600 V, making it the choice for work at the origin of an installation or on main switchboards. The CM4003 is rated CAT III 300 V but adds an analogue output for RMS and waveform recording, plus an external DC power input for long-duration unattended logging.

Can the Hioki CM4002 measure leakage on solar and VSD installations? Yes, and it includes a specific feature for it. Variable speed drives and PV inverters produce high-frequency capacitive leakage through their EMC filters, which inflates readings on an unfiltered clamp meter. The CM4002’s switchable low-pass filter (−3 dB at 180 Hz ±30 Hz) removes that high-frequency component, so the displayed value reflects the power-frequency leakage that a Type AC or Type A RCD actually responds to.

Does the Hioki CM4002 connect to a phone or tablet? Not on its own. Adding the optional Z3210 Wireless Adapter gives the meter Bluetooth® connectivity to Hioki’s free GENNECT Cross app for iOS and Android. From there you can view live readings, log events, display current harmonics to the 30th order, place readings onto site photographs, generate PDF reports on site, and push values directly into an Excel® file. The CM4002-90 model ships with the Z3210 included.

Does the Hioki CM4002 measure voltage? No. The CM4002 is a dedicated AC leakage current instrument and does not include a voltage measurement function. Electricians typically carry it alongside a multimeter or a multifunction installation tester rather than as a replacement for either.

What size cable does the Hioki CM4002 jaw fit around? The jaws accept conductors up to Ø40 mm in diameter, with internal jaw dimensions of 75 mm × 20 mm. That’s large enough for a three-phase-plus-neutral bundle on a submain, a single large cable, or several smaller circuits clamped together when isolating a fault by elimination.