Looking at leakage clamps

Online Editor

Discussing the similarities and differences between several AC leakage current clamps presently on the market

In any electrical installation, some current will flow through the protective ground conductor to ground, usually called leakage current. Leakage current most commonly flows in the insulation surrounding conductors and in the filters protecting electronic equipment. Leakage clamps measure the amount of leakage current flowing down the protective conductor of an appliance or installation.

Known for its expertise in high-end AC/DC current sensors, Hioki also offers a large variety of clamp meters, including three AC leakage current clamps. Before going into the details of what makes each of these leakage current clamps unique, let’s look at what they all have in common.

First, they all measure based on the TrueRMS principle, and they can all measure not only AC leakage and differential currents but also AC load currents. Bluetooth functionality can be added to each of the clamps with Hioki’s universal Bluetooth transceiver Z3210, allowing the clamps to communicate with smartphones and tablets running Hioki’s free “Gennect Cross” app. Hioki’s clamp meters are not only designed in Japan, but they are also made in the company’s own factory’s in Japan’s Nagano prefecture.

Reviewing the differences

So, let’s look at the differences between each of Hioki’s clamps, starting with the CM4001 leakage current clamp. With a height of just 16cm from top to bottom and jaws that have been engineered to make them as narrow as possible, you can use them even in the most confined spaces while still measuring on cables which are up to 24mm in diameter. Should it become too inconvenient to read the white backlight and crispy clear display, then an optional Bluetooth transmitter (Z3210) allows you to read (and of course also store) the measurement values on your smartphone

The smallest of the five current ranges is 60mA, with a guaranteed accuracy for values from 0.6mA. The largest current range of the CM4001 is 600A, the frequency band is from 40Hz to 1kHz and the measurement category is CAT III 300V. Even though the current clamp is so small, it is packed with functions like auto-hold, min/max/average, or an inrush current measurement feature. The CM4001 has been designed to be a small yet powerful and universal leakage current clamp, made to be used in small and confined spaces and requiring little room in your toolbox.

Measuring 23.3cm from top to bottom, the CM4002 leakage current clamp is not only more than 7cm taller then the CM4001, it is also bigger in width and depth. This is because the CM4002 has been designed to provide the most accurate measurement results while allowing it to be used on cables with a diameter of up to 40mm.

As a result, the smallest of six current ranges of the CM4002 is just 6mA with a guaranteed accuracy for values from 0.06mA, while the largest current range is 200A. The frequency band is also wider than that of its little brother, ranging from 15Hz to 2kHz, and the CM4002 complies to the IEC/EN 61557-13 standard which defines requirements for current clamps for measuring leakage currents in electrical installations, such as the protection against external magnetic fields (Class 2, magnetic fields ≤30A/m is what the CM4002 fulfils).

The third of the three leakage current clamp siblings from Hioki is the CM4003. Comparing the CM4002 with the CM4003 side-by-side, it is not easy to spot the differences between them. The physical dimensions are the same, and so are almost all technical specifications. It is easier to see the differences when comparing the two clamps side-by-side from a different view. The connector at the bottom of the CM4003 allows for a special adapter cable to be connected to the meter. This adapter cable converts the 4-pin outlet of the CM4003 to these two connectors:

  • A standard USB-C socket which allows you to power the CM4003 externally in case you want to perform longer term measurements. The power can come from an optionally available Hioki power supply unit, but nothing stops you from using any powerbank you would use to charge to charge your smartphone, for example.
  • A standard (male) BNC connector allows to output the measured current as a voltage which you can feed it into a memory recorder like Hioki’s MR8870.

The external connector of the CM4003 does impact its measurement category rating, which is CAT III 300V. In comparison, the CM4002 without the connector has a rating CAT IV 300V/CAT III 600V. The adaptor cable for the CM4003 leakage current clamp is called L9097 and it is included with every CM4003. The external USB power supply (Z1013) as well as the required USB-A-to-USB-C cable (L9510) are optional accessories. But again, the external power connector is a standard USB-C socket.

All three Hioki CM400x leakage current clamps are available as bundle versions which have the Z3210 Bluetooth transmitter already included, named CM400x-90.

Kai Scharrmann is at Hioki Europe.

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