Once the measurement principle behind leakage current testing is clear — covered in our leakage current testing guide — choosing the right instrument comes down to three practical specifications: resolution, range, and clamp aperture size.
Why Resolution Matters More Than Range Here
Leakage current readings are typically small — often single-digit to low double-digit milliamps for healthy equipment. A clamp meter built primarily for general-purpose load current work often doesn't have the resolution to meaningfully distinguish a 2mA leakage reading from a 5mA one. A dedicated leakage current clamp meter typically offers resolution down to 0.01mA or better, while still covering a usable range up to tens of amps for serious faults.
Range Considerations
Most dedicated leakage current meters offer a range spanning sub-milliamp resolution up to tens-of-amps. Check the resolution specified at the low end of the range specifically, not just the maximum range figure.
Clamp Aperture Size — A Frequently Overlooked Spec
Leakage current measurement requires clamping both the line and neutral conductors together, not a single conductor. The clamp aperture needs to be large enough to fit both conductors comfortably.
| Clamp aperture (approximate) | Typical application |
|---|---|
| Small (~16×18mm) | Densely packed control panels, individual small-gauge conductor pairs |
| Medium (~25×30mm to 35×40mm) | General branch circuit wiring, standard cable pairs |
| Large (~80×80mm and above) | Heavy cable bundles, multiple conductors, large-gauge supply cable |
AC, DC, or AC/DC Capable
An AC-only leakage clamp is adequate for general AC-powered installations. For mixed AC/DC environments — facilities with DC power systems, EV charging infrastructure, or solar installations — an AC/DC-capable instrument is necessary to avoid missing DC leakage current an AC-only clamp cannot detect.
Data Logging and Communication
For routine spot-check testing, a standalone clamp meter is sufficient. For trend monitoring or troubleshooting intermittent faults, an instrument with onboard data storage and a communication interface adds genuine diagnostic value.
Selection Summary
For routine periodic leakage testing, a mid-range AC leakage clamp meter with milliamp-level resolution and a matched clamp aperture covers most needs. For mixed AC/DC systems, an AC/DC-capable instrument is worth the additional cost. For fault investigation, prioritise data logging and a wider dynamic range.