As an Amazon Associate we earn from qualifying purchases.

Fluke 187 Explained: True RMS, Ratings, and Fuses

The Fluke 187 is a handheld True RMS digital multimeter. Fluke’s manuals describe it as a meter for measuring voltage, current, resistance, and other electrical quantities, with a rotary dial to select the function. The 187 and its sibling, the 189, share the same core design. The 189 adds features such as data logging, which Fluke’s Spanish user manual marks as available on the 189 only. If you only need the standard meter functions, the 187 covers them.

Quick answer

• A True RMS multimeter for AC and DC voltage, current, and resistance, according to Fluke’s manuals.
• Fluke’s Spanish user manual lists the meter as CAT III 1000 V and CAT IV 600 V, both at pollution degree 2.
• Fluke’s calibration manual lists a maximum input of 10 times the selected range, with a 1000 V maximum.
• The current inputs are protected by a 0.44 A fast fuse and an 11 A fast fuse. Check both before you measure current.

What True RMS means on the 187

A True RMS meter calculates the root-mean-square value of a waveform, so it reads AC voltage and current correctly even when the waveform is not a clean sine wave. Fluke’s calibration manual says the AC specifications are AC-coupled and true RMS, and are valid from 5 percent to 100 percent of each range. It also gives a crest factor of up to 3.0 at full scale. Crest factor is the ratio between a waveform’s peak and its RMS value, and a higher figure means the meter can handle sharper peaks.

True RMS matters when the load is not a simple resistor. A variable-speed drive, a computer power supply, or an LED driver can draw a distorted current that a basic average-responding meter misreads. A True RMS meter is designed for that case, but it does not remove the need to use the right category and range.

The ratings you need to check

Fluke’s Spanish user manual lists the safety rating as Overvoltage 1000 V Category III and Overvoltage 600 V Category IV, both at pollution degree 2. It cites EN 61010-1, and UL 3111-1 for the United States. The calibration manual gives a maximum input of 10 times the range, up to 1000 V maximum, and notes that noise at low frequencies and amplitudes can affect accuracy.

Read these ratings as limits. CAT III 1000 V means the meter is rated for distribution circuits such as a panel’s branch wiring up to 1000 V. CAT IV 600 V means the meter is rated for work at the source of the installation, such as the service entrance, up to 600 V. A meter with a higher category is safer for a higher-energy circuit; a meter used above its rating is not safe, however good the display looks.

Fuses: what Fluke’s documents list

The 187 uses fuses to protect its current inputs. Fluke’s Portuguese introductory manual lists a 0.44 A (440 mA) fast fuse rated 1000 V as F1, and an 11 A fast fuse rated 1000 V as F2. The Spanish user manual includes a warning to check the meter’s fuses before measuring current in a circuit, and has a section on testing and replacing fuses.

The fuses are a safety feature, not a convenience. If you measure current with a blown fuse, the meter may show a reading that looks normal. Fluke’s documents say to test the fuses before you measure current. Use only the fuse type the manual specifies. A fuse that is the wrong rating can leave the meter unprotected.

How to use it safely, step by step

1. Check the fuses first. Before you measure current, test the current fuses using the method in the Spanish user manual’s fuse-testing section. Replace a blown fuse with one of the specified rating.
2. Inspect the leads. Look for cracked insulation, exposed metal, or a worn tip. Replace damaged leads before use.
3. Match the input to the measurement. Use the voltage input for voltage, the current input for current, and never connect the probes across a voltage source while the leads are in the current jacks.
4. Select the category and range. Choose a meter category and voltage rating that match the circuit. Do not measure above the maximum input.
5. Verify the meter. Test the meter on a known live source before and after each set of readings, so you can tell the meter from the circuit.

Mains circuits can kill. Panel and service work belongs to a licensed electrician. A multimeter tells you what is present on a circuit; it does not make an energized panel safe to open, and it does not replace a lockout procedure.

Power and batteries

The 187 runs on a battery, and Fluke’s manuals describe a battery and fuse replacement procedure. Replace the battery when the low battery indicator appears, since readings taken on a weak battery should not be relied on for a safety decision. The manuals also describe a battery and fuse replacement chapter in the maintenance section, so keep the manual with the meter for reference.

How we chose

This article covers the Fluke 187 because it was the keyword requested. It draws on three Fluke documents we opened and read on 27 October 2026: the 187/189 calibration manual in English, the 187/189 user manual in Spanish, and the 187/189 introductory manual in Portuguese. Two of the three are in languages other than English, and the English calibration manual is written for service technicians. We did not compare the 187 with other meters in this article, and we did not rank it.

What we could not verify

• The sources we opened do not include an English user manual for the 187, so this article uses the Spanish user manual for ratings and fuse information.
• The sources do not give the battery life of the 187 in hours.
• The sources do not state a price, and this article does not cover price.
• The sources do not describe the meter’s behavior with every type of load, such as motors or electronic ballasts.

Buying checklist

• Check the category and voltage rating against the circuits you plan to work on. The Fluke documents list CAT III 1000 V and CAT IV 600 V.
• Decide whether you need data logging. Fluke’s manual says logging is a feature of the 189, not the 187.
• Confirm the current fuse ratings: 0.44 A and 11 A, 1000 V fast fuses.
• Check that the leads you plan to use carry a rating that matches the meter.

Mistakes to avoid

• Measuring current without checking the fuses first.
• Leaving the probes in the current jacks when you switch to a voltage measurement. This can blow a fuse or cause a short.
• Assuming a higher category rating means the meter is safe for any work. The rating is a limit, not a guarantee.
• Replacing a fuse with one of a different rating.

Related guides

• Best auto-ranging multimeters: a guide to meters that choose the range for you.
• Best multimeters for DC voltage: a guide for DC voltage checks such as batteries and solar circuits.

FAQ

Is the Fluke 187 a True RMS meter?

Yes. Fluke’s calibration manual describes its AC measurements as true RMS and AC-coupled.

What is the Fluke 187’s safety rating?

Fluke’s Spanish user manual lists CAT III 1000 V and CAT IV 600 V, both at pollution degree 2.

What fuses does the 187 use?

Fluke’s Portuguese manual lists a 0.44 A fast fuse and an 11 A fast fuse, both rated 1000 V.

What is the difference between the 187 and the 189?

Fluke’s Spanish user manual marks some features, such as logging, as available on the 189 only. Check each model’s manual for the full feature list.

Can I measure a voltage above 1000 V?

No. The calibration manual gives a maximum input of 1000 V.

How often should I replace the fuses?

Replace a fuse only when it blows or fails a test. Fluke’s documents describe a test and replacement procedure but do not give a replacement interval.

Bottom line

The Fluke 187 is a True RMS multimeter with a published rating of CAT III 1000 V and CAT IV 600 V. Its current inputs are protected by 0.44 A and 11 A fast fuses. Check the fuses before you measure current, match the category to the circuit, and do not measure above the stated input limit.

Sources

• Fluke Corporation, 187 and 189 True RMS Multimeter Calibration Manual (English), https://assets.fluke.com/manuals/187_189_cmeng0000.pdf (opened 27 October 2026)
• Fluke Corporation, 187 and 189 True RMS Multimeter Manual de uso (Spanish), https://assets.fluke.com/manuals/187_189_umspa0200.pdf (opened 27 October 2026)
• Fluke Corporation, 187 and 189 True RMS Multimeter Manual de introducao (Portuguese), https://assets.fluke.com/manuals/187_189_gspor0200.pdf (opened 27 October 2026)