In May 2022, Chauvin Arnoux’s Julian Grant published an article in Professional Electrician & Installer explaining the impact of harmonic currents on earth leakage, and how their effect can be mitigated by using the correct clamp meter.[1]

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Harmonics & Earth Leakage

In his article, Julian Grant explains that

“It stands to reason, after all, that if the current being drawn by a piece of equipment contains large amounts of harmonics, then the current that is leaking to earth will also contain them.”

He goes on to point out that currents at higher frequencies travel more easily through insulation and air gaps than currents at lower frequencies. This is due to the capacitive properties of insulation as well as the fact that the impedance of capacitors is inversely proportional to frequency (i.e., the higher the frequency, the lower the insulation resistance to AC currents). Due to this, there may be disproportionally more harmonics being leaked at higher frequencies than at lower frequencies (e.g., 50Hz).

Grant suggests that this presents two key problems when it comes to ensuring compliance with the IET wiring regulations:

  1. Accurately measuring earth leakage current
  2. Choosing the correct RCD type

Accurately Measuring Earth Leakage Current

As stated in section ii of the 531.3.2 regulation,

“…in order to avoid unwanted tripping by protective conductor currents and/or earth leakage currents, the accumulation of such currents downstream of the RCD shall be not more than 30% of the rated residual operating current.”

To measure earth leakage accurately, your earth leakage clamp has to support a scale wide enough to detect harmonics. For instance, if you wish to check harmonics up to the 25th order your clamp meter must have an upper limit of at least 1.25kHz, whereas users wishing to check the first 50 harmonics will need a clamp meter with a measuring bandwidth of 2.5kHz or more.

Choosing the Correct RCD Type

Ensuring your earth leakage clamp meter has a scale wide enough to account for harmonics is critical to choosing an appropriate protective device (RCD). Regulation 531.3.3 states,

“Different types of RCDs exist, depending on their behaviour in the presence of DC components and frequencies. The appropriate RCD shall be selected…”

The frequencies referenced in the regulation include harmonics. Therefore, if your clamp meter’s scale is too narrow it won’t include harmonics in the displayed earth leakage reading and the erroneous measurement may result in selecting an inappropriate RCD.

Chauvin Arnoux F65 Earth Leakage Clamp Multimeter

Julian Grant advises that a clamp meter with a bandwidth greater than 50x50Hz (2.5kHz) is required to include all necessary harmonics. That’s why Chauvin Arnoux has designed their F65 Earth Leakage Clamp Multimeter to measure AC leakage (resolution: 10mA) up to 3kHz which includes the 60th harmonic.

Grant goes on to suggest investing in a clamp meter with a feature that allows you to include and exclude harmonic currents from the total reading. This enables measurement of fundamental current and harmonic current; information that is vital for choosing an appropriate RCD. Chauvin Arnoux’s F65 Earth Leakage Clamp Multimeter has been specifically designed for measuring leakage currents that trip RCDs. To this end, it includes an Anti-harmonic filter for enhanced fault detection on disturbed systems. The Chauvin Arnoux F65 Earth Leakage Clamp Multimeter is ideal for measuring the harmonic leakage required for type F, B, & B+ RCDs.

At the top of the image, white text reads 'Earth Leakage Clamp Meter'. Beneath this a man in blue overalls and a yellow hardhat uses the F65 Clamp Meter to check a distribution board. Underneath a paragraph of text reads 'The 18th Ed. requires that we consider the size and type of leakage currents in our installations. This is very important when fitting new RCDs like types F, B or B+ that detect leakage at higher frequencies. Using the F65 ensures you capture all AC leakage up to and beyond the 50th harmonic.' Beneath this paragraph in larger text it reads 'One of the only leakage clamps to measure total AC leakage including harmonics up to 3kHz.' To the right is an image of the F65 Clamp Multimeter and four bullet points that read '* Measures harmonic leakage required for Type F, B & B+ RCDs; * Total AC leakage up to 3kHz (60th Harmonic); * Multimeter Functions (AC mA, AC A, AC/DC V, Hz, Ω, Continuity); * Compact and Rugged Design; * Backlight for low light conditions'. At the bottom of the image is the Chauvin Arnoux logo, address, telephone number, and email.

In addition to this, Chauvin Arnoux's F65 Earth Leakage Clamp Multimeter includes several other useful features such as:

  • Voltage, frequency, resistance, and continuity measurement
  • A compact and rugged design
  • Backlight

Further Information

At PASS Ltd, we offer a wide array of Chauvin Arnoux products including the F65 Earth Leakage Clamp Multimeter. For more help and advice regarding Chauvin Arnoux’s range of instruments, please contact our Sales team on 01642 931 329 or via our online form.

To read Julian Grant’s full article, please click here.

Footnotes

[1] Information and quotes for this blog were gathered using the following source: