Fluke 789 vs Fluke 1587 FC: Process Calibration or Insulation Testing?

Specs side by side

Specs checked against manufacturer documentation and official Amazon listings. Desk research, not bench testing. How we research.

Key differences

• →Purpose: the 789 is a loop calibrator built into a multimeter; the 1587 FC is an insulation tester built into a multimeter. Neither can do the other's specialist job.
• →Output: the 789 drives up to 24 mA at 24 V compliance into a loop; the 1587 FC drives about 1 mA at 50 to 1000 V DC into insulation.
• →mA reading: the 789 resolves 0.001 mA at 0.05% + 2 and shows % of span; the 1587 FC reads mA at ±(0.2% + 2) with no span display.
• →Meter extras: only the 1587 FC lists capacitance, temperature, a low-pass filter and built-in Fluke Connect.
• →Shared: CAT IV 600V / CAT III 1000V, True RMS AC, four AA cells, the same 50 × 100 × 203 mm footprint, no 10 A input and a 3-year warranty.

A loop on one side, a winding on the other

It helps to picture where each meter gets clipped on. An instrument technician puts the 789 in series with a running loop, or on the terminals of a transmitter sitting on a workbench, and the circuit stays energized the whole time because the 24 V loop is the thing being checked. An electrician uses the 1587 FC the other way around: the feeder gets switched off, locked and proven dead, and only then does the meter put its own high voltage onto the winding or cable. One tool works with the power on; the insulation function only works with it off.

We haven't hands-on tested either tool. The 789 carries a 4.7 and the 1587 FC a 4.6 from desk research, and every number here comes from Fluke's data sheets, product pages and 789 manual, or the official Amazon listings, as recorded in our existing Fluke 789 and 1587 FC comparisons.

What each tool puts out

Both meters push current into something, which is exactly why they can't stand in for each other. The 789 is a precise current source with a modest voltage behind it. The 1587 FC is a high-voltage source with a deliberately small current limit. Plotted together, the voltage gap is about forty to one.

Two details are worth knowing. The 1587 FC's test voltage tolerance is +20% / −0%, so the 1000 V setting is allowed to land anywhere from 1000 V up to 1200 V, never below. And the 789's compliance figure depends on which Fluke document you read: the data sheet and product page say 24 V, while the 789 manual says 28 V with a healthy battery. Either is enough for typical loop loads; Fluke rates the source at 1,200 Ω at 20 mA.

Can the 1587 FC check a 4–20 mA loop?

Partly. Its 60 mA range will read loop current if you break the loop and wire it in series, so it can tell you a transmitter is outputting roughly 12 mA. What it can't do is generate a signal, so there's no way to drive a PLC input to 4, 12 and 20 mA and watch the scaling, stroke a valve, or power a transmitter that has no supply. Precision differs too. Here is the worst-case error on a 12 mA reading, from each meter's published accuracy:

For troubleshooting, ±0.044 mA is still plenty to tell a dead transmitter from a working one. For calibration against a tolerance of a few tenths of a percent, it isn't. Fluke doesn't publish the 1587 FC's resolution in the sources we used, so the 0.01 mA count is our reading of a 6000-count display on a 60 mA range. Our guide to measuring milliamps shows the series connection either meter needs.

Can the 789 tell you a motor is safe to restart?

No. Its resistance function tops out at 40 MΩ and uses the meter's own small test voltage, which can show a dead short between a winding and the frame but says little about insulation that only breaks down under stress. A proper insulation test applies hundreds of volts precisely because weak insulation often looks perfect at a few volts. The 1587 FC does that at five settings, reads up to 2 GΩ, and runs timed PI and DAR tests whose results land in the Fluke Connect app with temperature compensation.

The 789 also lacks the motor-side extras Fluke lists for the 1587 FC: capacitance for run capacitors, temperature with the included K-type probe, and a low-pass filter for reading a drive's output. For the winding-test procedure itself, see how to check a motor winding for a short, and for how the 1587 FC compares with Fluke's simpler insulation model, read Fluke 1577 vs Fluke 1587 FC.

Who should buy neither

Most people who search for these two model numbers don't need either one. If your day is outlets, breakers, lighting, HVAC controls or motor running current, both specialists come up short in the same place: the 789 tops out at 1 A (0.44 A continuous) and the 1587 FC at 400 mA, with no 10 A jack on either. You would be paying for a calibrator or a megohmmeter you never switch on, and still need a clamp for load current.

The Fluke 117 and 87V are the two general meters on this list that we have hands-on tested; see the Fluke 117 review and Fluke 87V review. Each specialist is also compared head to head with the 87V in Fluke 789 vs Fluke 87V and Fluke 1587 FC vs Fluke 87V, and our clamp meter buying guide covers current measurement.

Fluke 789 vs 1587 FC: which should you buy?

If you need both functions, carrying both is the honest answer: they share a footprint and battery type, and nothing Fluke publishes for either one covers the other's core task. If you're still weighing loop tools, the Fluke 787B vs Fluke 789 page covers the cheaper ProcessMeter without loop power, and our best multimeters for 4–20 mA loop testing adds clamp-on options. For electrical shortlists, start with the best multimeter for electricians.

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