Product Nov. 28, 2019

Hioki Launches AC Clamp Meter CM3281 and CM3291

Introducing a Pair of AC Ammeters Engineered to Accommodate Large-Diameter Cables with All the Ease of Use You’ve Come to Expect from Hioki

November 28, 2019 - Nagano, Japan

Hioki is pleased to announce the December 2019 launch of the AC Clamp Meter CM3281 and CM3291, a pair of large-diameter AC ammeters featuring a more compact jaw (sensor) design that makes them easier to insert between wires in confined spaces.

The previous AC Clamp Meter CM3289 (⌀33 mm, rating of 1000 A AC) featured a low-profile design that was engineered to enable users to clamp around wires easier. The new instruments build on that product’s design by increasing both the jaw diameter (⌀46 mm) and the current capacity (by increasing the rating to 2000 A AC). Both new models preserve the CM3289’s ease of use so that thick cables (paired wires, etc.)1 are easily measured.

Hioki has redesigned the jaw (sensor) profile as part of an effort to expand its clamp meter line with models that are easier than ever to clamp around wires. The newly designed clamp meters have won broad praise, including an honorable mention in the 58th Product Competition at Electrical Construction Equipment and Materials (JECA) Fair 20192 and a 2019 Good Design Award3.

Although Hioki has recently updated many of its clamp meters, up until now only one low-profile model has been capable of measuring thick cables (paired wires, etc.). To address this issue, Hioki developed the CM3281 (mean value rectification method) and CM3291 (true RMS method) to enlarge the 33 mm diameter and 1000 A AC current rating of the AC Clamp Meter CM3289 to 46 mm and 2000 A AC, respectively.

1. Designed to accommodate larger-diameter wires without compromising ease of use
The CM3281 and CM3291 are as easy to clamp around wires as their predecessor, the CM3289. Since their jaws are only 8.3 mm thick, they can be easily clamped around wires in confined spaces. And since they can accommodate conductors with a diameter of up to 46 mm, they can measure thick wires (for example, paired wires) that would require use of an option with the previous CM3289.

2. Built tough for use in the field
Thanks to a broad operating temperature range of -25°C to 65C°, the CM3281 and CM3291 can be used almost anywhere. What’s more, drop-proof construction means the instruments can withstand being dropped onto concrete from a height of 1 m.

 3. Ability to measure up to 2000 A AC using either the mean rectification method or the true RMS method
The CM3281 uses the mean rectification method to generate indicated values that approach the fundamental wave component.  On the other hand, the CM3291 uses the true RMS method, which yields accurate values even when the AC current waveform is distorted, for example due to use of an inverter or switching power supply.  Customers can choose the model (measurement method) that best suits their application.

4. Ability to measure both current and voltage
The CM3281 and CM3291 can measure a variety of parameters besides AC current in a single unit, including AC/DC voltage, continuity, and resistance.

Equipment maintenance inspections

1 Paired wires: Cables that have been split into two wires in order to carry a large current.

2 Electrical Construction Equipment and Materials (JECA) Fair: Japan’s largest electrical equipment exhibition. The event is organized by the Japan Electrical Construction Association with sponsors including the Ministry of Land, Infrastructure, Transport and Tourism; the Ministry of Economy, Trade and Industry; and the Ministry of the Environment. The AC/DC Clamp Meter CM4376 received a JECA honorable mention in a previous exhibition’s Product Competition. Hioki products have received a total of 9 awards since the 44th fair in 1996.

3 Good Design Awards: A comprehensive design assessment and recommendation program organized by the Japan Institute of Design Promotion with more than 50 years of history. The AC/DC Clamp Meter CM4375/CM4376 and AC Clamp Meter CM4141/CM4142 received 2019 Good Design Awards.


Established in 1935, HIOKI E.E. CORPORATION (TSE: 6866) has grown to become a world leader in providing  consistent delivery of test and measuring  instruments through advanced design, manufacturing, and sales and services. By offering over 200 main products characterized by safety and quality while meeting an expansive range of applications, we aim to contribute to the efficiency  and value of our customers' work  in research and development, production and electrical maintenance. HIOKI products and services are available around the world through our extensive network of subsidiaries and distributors. Information about HIOKI is available at

CM3291 AC Clamp Meter

Easily measure thick cables and paired wires