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Fluke i400 Review: 400A AC Current Clamp Accessory

The Fluke i400 turns a digital multimeter into an AC clamp meter. This review explains how the 1 mA per amp output is read, what the accessory can and cannot measure, and when a dedicated clamp meter is the better purchase.

By the Akermin Editorial Team · 4 min read

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Fluke i400 Review: 400A AC Current Clamp Accessory

Fluke · Fluke i400 400 Amp AC Current Clamp

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

Verdict

The Fluke i400 is a current transformer in a clamp with a pair of leads. Plugged into a multimeter’s milliamp input, it delivers 1 mA for every amp flowing in the conductor inside its jaw, so the meter’s AC milliamp reading is the current in amps. The manufacturer specifies it to 400 A AC, a 20 mm maximum conductor diameter and a CAT III 600 V rating. For someone who already owns a Fluke 117 or 179 and occasionally needs to read a motor or feeder current, it is the lowest-cost way to add clamp measurement without a second meter. It reads AC only, and the multimeter has to be set correctly each time. For daily current work, a dedicated clamp meter is quicker; for occasional use, the documentation supports the i400 as the sensible accessory.

Who It Is For

  • Owners of a good multimeter who need occasional AC current readings without breaking the circuit.
  • Technicians who want to log current with a meter that already has min/max recording.
  • Educators and students who benefit from seeing the transformer ratio explicitly.

Documented Specifications

Item Documentation
Type AC current clamp accessory for digital multimeters
Output 1 mA per amp
Range 400 A AC (manufacturer; one listing bullet says 200 A)
Maximum conductor diameter 20 mm
Safety rating CAT III 600 V

How a Clamp Accessory Works

The i400 is a current transformer: the conductor in the jaw is the primary winding, the coil inside the clamp is the secondary, and the ratio is set so that the secondary delivers 1 mA per primary amp. The multimeter measures that secondary current on its milliamp range. Because the ratio is 1000:1, a 6000-count meter on its 600 mA range resolves 0.1 mA, which corresponds to 0.1 A in the conductor. Small currents below an amp or so are therefore hard to resolve, and the accessory is at its best from a few amps upward. The output must be connected to the meter before the jaw is closed on a live conductor; an open-circuited current transformer can develop a high voltage. For the general procedure see measuring current with a clamp meter.

A Note on the Listing

The Amazon listing title and the manufacturer’s documentation describe the i400 as a 400 A clamp; one feature bullet on the listing says up to 200 A. We have gone with the manufacturer’s figure. The lesson is a general one: when a listing contradicts itself, the datasheet is the authority, and it is worth downloading it before relying on a range figure.

Limits of the Accessory Approach

Three things make a dedicated clamp meter more convenient. First, there is no DC: the transformer principle needs an alternating field. Second, every reading requires the meter to be on the right range and the mental conversion, which is trivial once but tedious across a panel. Third, the 20 mm jaw is smaller than the 30 mm of a Fluke 323 or 325 and fits fewer feeder cables. Against those, the i400 costs a fraction of a clamp meter and turns a meter with min/max/average recording, such as the Fluke 179, into a current logger.

Practical Notes

Set the multimeter to AC milliamps before closing the jaw and connect the i400 leads first; the meter must be on a current range rather than a voltage range for the reading to make sense. The i400’s output is small, so the meter’s current fuse is not at risk from the accessory itself. For a small load, a few turns of the conductor through the jaw multiply the reading: three turns give 3 mA per amp, and the display is divided by three. That trick recovers resolution on control circuits. Keep the jaw faces clean, because dirt on the mating surfaces lowers the reading, and store the clamp with the jaw closed.

Strengths

  • Adds clamp current to a multimeter you already trust.
  • Simple 1 mA per amp ratio, easy to read.
  • CAT III 600 V rating.
  • Lower cost than a second meter.

Limitations

  • AC only.
  • Smaller jaw than dedicated clamps.
  • Poor resolution below a few amps on a typical multimeter range.

How It Compares

The Fluke 323 is the dedicated 400 A AC clamp with voltage and continuity in one body. The Fluke 117 and Fluke 179 are the multimeters most often paired with the i400. If DC current is needed, the Fluke 325 is the compact answer.

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. Related: choosing a digital multimeter.

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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

How do I read the i400 on a multimeter?

Plug it into the milliamp input, set the meter to AC milliamps, and read the display: 1 mA on the meter equals 1 A in the conductor. A reading of 12.5 mA means 12.5 A.

Does the i400 measure DC current?

No. It is a current transformer type clamp and responds to AC only. For DC through a jaw you need a Hall-effect clamp meter such as the Fluke 325.

What is the current limit?

The manufacturer specifies the i400 as a 400 A AC clamp. One bullet in the Amazon listing refers to 200 A; the product name and Fluke's documentation state 400 A, so treat the listing bullet as an error.

Will it work with non-Fluke meters?

Any meter with an AC milliamp range and standard 4 mm safety input jacks can read it, subject to the meter's own rating.

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