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Review

Extech MA443 Review: 400A True-RMS AC Clamp Meter

The Extech MA443 sits between the MA440 and the MA445. The current Amazon listing is the MA440; this review explains how the three models differ, what a True RMS AC-only clamp is for, and who should choose each.

By the Akermin Editorial Team · 4 min read

As an Amazon Associate, Akermin earns from qualifying purchases. Product links on this page are affiliate links.

Verdict

The Extech MA443 is a compact 400 A AC clamp meter with True RMS measurement, a non-contact voltage detector, resistance, frequency and continuity, and a 4000-count display. It is the middle model of a three-meter family. The Amazon listing at the time of writing is for the MA440, the base model; the MA445 is the AC/DC model with a 40000-count display and inrush capture. The manufacturer positions the MA443 as the True RMS AC version, which is the one to choose for an electrician whose panels are full of LED drivers, electronic ballasts and drive-fed motors and who does not need DC current. If the MA443 is not available to you, the MA445 covers everything it does and adds DC; the MA440 is adequate for resistive loads only.

MA440, MA443 and MA445

Item MA440 MA443 MA445
AC current to 400 A Yes Yes Yes
DC current No No Yes
True RMS Listing says yes; check the datasheet Yes (manufacturer) Yes
Display 4000 count 4000 count (manufacturer) 40000 count, dual
Inrush capture No No Yes
Non-contact voltage detector Yes Yes Yes
Amazon US listing Yes Not at the time of writing Yes

A note on the MA440: Extech’s own material has historically described it as the base AC model, while the current Amazon listing describes it as True RMS. Check the datasheet for the specific unit you are buying before relying on it for non-linear loads.

Documented Specifications

Item Documentation
Current AC to 400 A, True RMS (manufacturer)
Functions AC current, resistance, frequency, continuity (family listing)
Non-contact voltage Built-in NCV detector
Display 4000-count backlit display with data hold (family listing)

The voltage range, jaw opening and safety category rating are on the manufacturer’s datasheet; consult the current revision before relying on a figure.

Why True RMS Matters on an AC-Only Clamp

An average-responding meter rectifies the current waveform, averages it and scales the result by the ratio that applies to a sine wave. On a resistive heater that is exact. On a circuit full of LED drivers, computers or a drive-fed motor, the current is drawn in narrow peaks and the sine-wave ratio no longer applies; the average-responding meter reads low, sometimes by a large fraction. A True RMS meter computes the heating value of the waveform directly and reads correctly regardless of shape. Because most modern loads are non-linear, True RMS has moved from a premium feature to a baseline one, and it is the reason the MA443 exists as a separate model from the MA440. See choosing a clamp meter for the other specifications that matter.

NCV, Frequency and Continuity

The non-contact voltage detector lights when the jaw tip is near an energised AC conductor, which is useful for finding the live cable in a bundle before clamping; it is a screening tool and a contact measurement should follow. Frequency confirms whether a circuit is on the mains or on a drive or inverter. Continuity with an audible tone covers the basic conductor checks. Data hold captures a reading taken where the display cannot be seen. These are the functions of a straightforward electrician’s clamp, and owners of the family generally describe them as adequate rather than exceptional. For the technique see measuring current with a clamp meter.

Practical Notes

A clamp only reads a single conductor; a two-conductor cable in the jaw reads near zero. For appliance loads a line splitter is needed. The compact body is easy to hold one-handed in a residential panel, and the backlit display is readable in a dim closet. Owners of the family note that the NCV detector is sensitive enough to trigger on adjacent live cables in a crowded panel, so it is best used on a single separated conductor.

Strengths

  • True RMS AC current in a compact, lower-cost clamp.
  • Non-contact voltage detector built in.
  • Simple function set with few selector positions.

Limitations

  • No DC current.
  • Not currently listed on Amazon US; the MA440 and MA445 are.
  • No inrush capture, temperature or capacitance.

How It Compares

The Extech MA445 adds DC current, a 40000-count dual display and inrush for a modest premium and is the safer purchase if any DC work is likely. The Extech MA120 is the mini AC/DC clamp for tight spaces. The Fluke 323 is the closest Fluke equivalent: True RMS AC only, 400 A, with a clearer published safety rating and a higher price.

How We Research

This review is based on the manufacturer’s published documentation for the MA440 family, the Amazon listings for the MA440 and MA445, and owner reports. We did not run laboratory tests.

Extech MA440 400A AC Clamp Meter with NCV, True RMS, 4000 Count | 400A AC, True RMS, NCV, resistance, frequency, continuity, 4000-count backlit, compact, leads, case

Extech MA440 400A AC Clamp Meter with NCV, True RMS,

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Extech MA445 400A True RMS AC/DC Clamp Meter, NCV, 40000 Count | 400A AC/DC, True RMS, NCV, inrush, frequency, duty cycle, diode, continuity, 40000-count dual, 1.2in jaw

Extech MA445 400A True RMS AC/DC Clamp Meter, NCV, 40000

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Extech MA120 200A AC/DC Mini Clamp Meter with Voltage Detector | 200A AC/DC, built-in NCV with LED, data hold, MIN/MAX, relative mode, compact, auto power off

Extech MA120 200A AC/DC Mini Clamp Meter with Voltage Detector

View on Amazon

Products shown because their documented specifications fit this guide. Price and availability are on Amazon and can change.

Frequently Asked Questions

Is the MA443 the model on Amazon?

The current Amazon listing in this family is the MA440. The MA443 is the True RMS AC version and the MA445 is the True RMS AC/DC version. All three share the compact body and the non-contact voltage detector.

What does True RMS add on an AC-only clamp?

Correct readings on non-sinusoidal current, which is what LED lighting, drives and switch-mode power supplies draw. An average-responding clamp reads low on those loads.

Does the MA443 measure DC current?

No. For DC current through the jaw you need the MA445 or another Hall-effect clamp.

Which one should an electrician buy?

For AC panel work with modern loads, the MA443. For automotive, solar or DC control circuits, the MA445. The MA440 is the base model for simple resistive loads.

Affiliate disclosure: Akermin earns a commission from qualifying Amazon purchases made through links on this page. Our editorial picks are based on documented specifications and owner feedback, not commissions.