Clamp Meters Selection Guide
Clamp meters are divided into AC-only, AC/DC, fork, flexible-clamp and leakage current types; selection looks at criteria such as the current range.
This guide explains what to look at when choosing products in the Clamp Meters category.
Clamp meter types
- AC-only models. They work on the current transformer principle; this design gives results only on alternating current. They are sufficient for mains-fed panel and motor circuits.
- AC/DC models. A Hall-effect sensor also measures direct current; this is needed for battery banks, solar panel strings and DC drive circuits. The zero function that clears the residual value on the display before a DC measurement is stated separately in the product data.
- Fork type (open jaw). The jaw does not open; the conductor is taken between the prongs of the fork, which makes one-handed measurement easier on closely packed cables. In product names it appears with ranges such as 60 A and 200 A.
- Flexible clamp. A flexible coil without a core does not saturate; it is wrapped around wide busbars and thick cables. This category has a model with a 3000 A range; a flexible-clamp ammeter is also listed under ammeters and voltmeters.
- Leakage current meter. These are clamps that measure with milliampere-level resolution; the product data includes resolution values of 0.01 mA, 0.1 mA and 1 mA.
What to look at when choosing a clamp meter
- Current range. The value in the product name (such as 400 A, 600 A, 1000 A) is the highest range and must cover the largest expected current. For small currents the lower ranges are decisive; the data of some models lists the 3 A and 30 A ranges separately with their own accuracy values.
- Jaw opening. The outer diameter of a single core or the width of a busbar must fit in the jaw. The product data includes values such as 17 mm for mini models, 28 mm and 30 mm for 400 A and 600 A models, and 42 mm, 63 mm and 75 mm for high-current models.
- True RMS. The current of non-linear loads such as variable frequency drives, electronic ballasts and computers is not sinusoidal; a clamp that works on the average value reads this current incorrectly, so a True RMS model is chosen for these loads. If voltage will also be measured at the drive output, look for the VFC or low-pass filter (LPF) function in the data.
- Accuracy and display count. Accuracy is written in the form ±(2%+5), as a percentage of the reading and a count margin on the last digit; because the count margin is fixed, the relative error of a small current on the same range increases. The display count appears in the data with values such as 6000, 4000, 2000 and 9999.
- Measurement category. The data includes values such as CAT III 600 V and CAT III 1000 V / CAT IV 600 V. Measurements at the distribution board and in fixed installations fall under CAT III, and measurements at the meter and on the main overcurrent protection side fall under CAT IV; the required class is determined according to the project and manufacturer data.
- Additional measurements. Inrush measurement for motor starting current, non-contact voltage detection (NCV), a low-impedance voltage range (LoZ), temperature, capacitance and Bluetooth connectivity vary by model.
- Supply. The battery size is written in the data with an IEC code: R03 is the AAA battery, R6 and LR6 are the AA battery, and 6F22 is the 9 V battery size.
Points to watch for a correct reading
- Clamp a single conductor. The clamp reads the vector sum of the currents of all conductors passing through the jaw; if a multicore cable is clamped by its outer sheath, the load current is not read. Measure at a terminal block or switch output where the cores can be reached one by one.
- Zero before a DC measurement. In clamps with Hall sensors, the residual magnetism left in the jaw is added to the reading; the zero function clears this value.
- The jaw must close completely. A gap or dirt between the jaw tips distorts the reading.
To compare the measured current with the value expected from the rated power on the load's label, you can use the active power to current and fuse calculation tool.
Measuring instruments that look similar
- The clamp-type earth testers under earthing measuring instruments resemble a clamp meter, but they measure earth resistance, not current.
- For current measurement made by connecting in series with the circuit, digital multimeters are in a separate category.
- Spare probes and test leads are in the measuring instrument accessories category.
Brand and order notes
- The clamp meters in this category are of the Unit brand; the model code (for example UT204+, UT210E) is written in the product name and can be used in search.
- Products are sold by the piece.
- For models listed with a lead time, the delivery time is confirmed before ordering.
Comparison and selection table
| Selection Criterion | Standard AC Clamp Meter | AC / DC True RMS Clamp Meter | Leakage Current (mA) / Flexible Rogowski Clamp |
|---|---|---|---|
| Current Capability | AC current only (400 A – 1000 A) | Both AC and DC current (400 A – 1000 A Hall-effect sensor) | Micro-resolution mA leakage (0.01 mA) or flexible coil (3000 A) |
| Waveform Accuracy | Average-responding or True RMS models | True RMS (accurate on distorted VFD & non-linear loads) | True RMS with low-pass filter or flexible loop for tight busbars |
| Jaw & Extra Functions | 25–40 mm jaw; AC/DC voltage, resistance, continuity | DC Zero button, motor Inrush capture, capacitance, Hz | Earth leakage diagnostics or wrapping around multi-cable bundles |
| Typical Application | General building maintenance, AC motors & PFC panels | Solar PV strings, battery banks, UPS, automotive & VFDs | Troubleshooting nuisance RCD trips & heavy busbar risers |
Frequently asked questions
Does a clamp meter measure DC current?
Not every model does. Clamps that work on the current transformer principle measure only alternating current. For direct current you need models that use a Hall-effect sensor and state AC/DC and DC current measurement in the name or data. If you will measure on a battery, solar panel or DC drive circuit, check that the product data includes a DC current range.
How is ±(2%+5) accuracy interpreted?
The first number is a percentage of the reading, and the second number is the count margin on the last digit of the display. For a reading of 100.0 A at 0.1 A resolution, the 2% margin is 2.0 A and 5 counts equal 0.5 A; the true value can be between 97.5 A and 102.5 A. When 5.0 A is read on the same range, the margin is 0.6 A, so the relative error grows noticeably.
How are small currents measured with a clamp meter?
For small currents, the resolution of high-range clamps may be insufficient. If the conductor is passed through the jaw several times, the reading is multiplied by the number of turns; the true current is found by dividing the reading by the number of turns, although accuracy drops somewhat. For continuous small-current measurement, low-range mini models or a multimeter connected in series with the circuit are more suitable. For leakage currents at the milliampere level, leakage current clamps are listed in this category.
What is inrush current measurement used for?
Loads such as motors and transformers draw a short-term current above their continuous operating current at the moment they are switched on. The normal measurement mode cannot capture this brief peak value. Clamps with an inrush function capture the initial current and hold it on the display. This value is used to investigate protective devices that trip during starting and starting problems.
Is a clamp-type earth tester the same as a clamp meter?
No. Although they look alike, a clamp-type earth tester measures the resistance of the earthing loop in ohms through the earthing conductor it grips. A clamp meter, on the other hand, shows the current passing through the conductor in amperes. Some earth testers can also show leakage current, but a clamp meter cannot measure earth resistance. Earth testers are listed in the earthing measuring instruments category.