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Extech MA445 Review: 400A True-RMS AC/DC Clamp Meter

The Extech MA445 packs a 40000-count display, inrush capture and AC/DC current into a compact 400 A clamp. This review explains why the display count matters, what inrush adds for motor work, and how the MA445 compares with the MA440, MA443 and Fluke 325.

By the Akermin Editorial Team · 4 min read

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Extech MA445 Review: 400A True-RMS AC/DC Clamp Meter

Extech · 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

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Price and availability are shown on Amazon and can change at any time.

Verdict

The Extech MA445 is a compact 400 A clamp meter that reads AC and DC current with True RMS, shows readings on a 40000-count backlit dual display, captures inrush current, and adds frequency, duty cycle, diode test, continuity and a non-contact voltage detector. The 1.2 inch jaw fits the conductors found in residential and commercial panels. Against the Fluke 325 it offers more display resolution and inrush capture at a lower price, with a less established reputation and no temperature or capacitance stated on the listing. Against its own siblings, the MA440 and MA443, it is the one to choose when DC current or fine resolution is needed. For an electrician or HVAC technician who wants a capable everyday clamp, the documentation supports it.

Who It Is For

  • Electricians who want AC and DC current with fine resolution in one compact clamp.
  • HVAC technicians who diagnose hard-starting motors with inrush capture.
  • Solar and automotive technicians who need DC current below 400 A.

Our guide to choosing a clamp meter explains which functions each trade actually uses.

Documented Specifications

Item Documentation
Current AC and DC to 400 A, True RMS
Display 40000-count backlit dual display, primary and secondary readings
Non-contact voltage Built-in NCV detector
Functions Inrush current capture, frequency, duty cycle, diode test, continuity
Jaw opening 1.2 inch

The voltage and resistance ranges and the safety category rating are on the manufacturer’s datasheet; consult the current revision.

Why 40000 Counts Matter on a Clamp

Display count is the largest number the display can show before changing range. A 4000-count meter on a 400 A range shows 399.9 at most, so it resolves 0.1 A. A 40000-count meter shows 399.99 and resolves 0.01 A. On a 40 A range that becomes 0.001 A. The practical benefit is on small loads: a control transformer drawing 0.35 A reads as 0.3 or 0.4 on a 4000-count meter and as 0.35 on the MA445. It also means small changes, such as a motor’s current creeping up as a bearing fails, are visible earlier. Resolution is not accuracy; the manufacturer’s accuracy specification still applies. But within that specification, more digits give more information. See measuring current with a clamp meter.

Inrush Capture and the Dual Display

A motor draws several times its running current in the first fraction of a second after it starts. That surge trips breakers, dims lights and, when it grows over time, signals a failing motor or capacitor. Inrush capture records it so it can be compared with the breaker’s trip curve and the motor’s rating. The dual display shows two values at once, typically current with frequency or voltage, which saves switching functions on a drive-fed motor where both matter. Duty cycle reads the on-time ratio of a pulsed signal, which is relevant to fuel injectors, PWM fan controls and some lighting drivers.

DC Current and NCV

DC through the jaw uses a Hall-effect sensor and needs zeroing before each reading; the meter provides a zero function. Within 400 A it covers automotive, marine, solar string and battery circuits. The built-in non-contact voltage detector screens for live conductors before clamping and should be followed by a contact measurement. Our article on measuring solar panel current shows the DC procedure.

Practical Notes

A 40000-count display shows more digit movement on a fluctuating load than a 4000-count meter, so the hold function is the answer for a reading that will not settle. Inrush capture must be armed before the motor starts, since the surge lasts only a fraction of a second; owners describe setting the meter, clamping, and then having a colleague start the unit. For DC, zero the meter with the jaw closed on nothing and keep the conductor centred. The dual display can be set to show frequency alongside current on drive-fed motors, which is the combination most owners leave it on.

Strengths

  • 40000-count dual display gives fine resolution and two values at once.
  • AC and DC current with True RMS.
  • Inrush capture for motor diagnostics.
  • NCV detector and a compact body.

Limitations

  • Temperature and capacitance are not stated on the listing.
  • 400 A ceiling.
  • No wireless logging.

How It Compares

The Extech MA443 is the True RMS AC-only sibling with a 4000-count display for those who never need DC. The Extech MA120 is the mini AC/DC clamp for tight spaces at 200 A. The Fluke 325 matches the 400 A AC/DC capability and adds temperature and capacitance with Fluke’s documentation and support.

How We Research

This review is based on the manufacturer’s published specifications, the Amazon product listing 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 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

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Fluke 325 True-RMS Clamp Meter with Frequency, Temperature & Capacitance Measurements

Fluke 325 True-RMS Clamp Meter with Frequency, Temperature & Capacitance

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

Frequently Asked Questions

What does a 40000-count display give me?

More digits at each range. On a 400 A range a 4000-count meter resolves 0.1 A; a 40000-count meter resolves 0.01 A. That matters for small loads and for seeing small changes.

What is the dual display for?

It shows a primary and a secondary reading at once, for example current and frequency, so you do not have to switch functions to see both.

How is the MA445 different from the MA440 and MA443?

The MA440 and MA443 are AC-only clamps. The MA445 adds DC current, the 40000-count display and inrush capture. All three have a non-contact voltage detector.

Does it capture inrush?

Yes. The listing includes inrush current capture, which records the start-up surge of a motor or other inductive load.

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.