Fluke 1555 Explained: Insulation Testing, Ratings and Safe Use
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Fluke 1555 Explained: Insulation Testing, Ratings and Safe Use
The Fluke 1555 is an insulation resistance tester, sometimes called a megohmmeter. It applies a test voltage to insulation and reads the resulting resistance. The manual describes it as an insulation resistance tester, not a general multimeter. The Fluke documents we opened describe it with six preset test voltages up to 10,000 V, resistance measurement up to 2 TΩ, and a CAT IV 600 V rating. This page covers those figures, the safety steps the manual asks for, and the checks to make before you buy a 1555 rather than a 1550C.
Quick answer
- The 1555 applies a test voltage and measures insulation resistance, with polarization index and dielectric absorption ratio functions.
- Its six preset test voltages run from 250 V to 10,000 V. The 10,000 V preset is marked in the manual as a 1555-only feature.
- The printed category ratings are CAT III 1000 V and CAT IV 600 V, with EN 61557 and EN 61010-1 compliance.
- The tester does not indicate the presence of hazardous voltage. Read the warnings before each test, and confirm the circuit is de-energized and discharged.
What the 1555 measures
The manual lists insulation resistance measurement from 200 kΩ up to 2 TΩ. It also offers a polarization index (PI) and a dielectric absorption ratio (DAR), which compare readings taken over time to show how the insulation is changing. A ramp mode raises the test voltage at 100 V per second. The tester also indicates breakdown voltage, has a timer, and stores results with a user-defined ID tag. An infrared port and PC software allow results to be downloaded.
The Users Manual covers the battery charge, preset and programmed test voltages, the steady-state and ramp tests, the polarization index, the dielectric absorption ratio and the capacitance function. Stored results can be tagged and downloaded.
Published ratings and figures
The table uses only figures printed in the three Fluke documents we opened. Where a document does not state a figure, the cell says so.
| Item | What the Fluke documents state | Where it is printed |
|---|---|---|
| Preset test voltages | 250 V, 500 V, 1000 V, 2500 V, 5000 V and 10,000 V (10,000 V marked 1555 only) | Users Manual, PN 3593019 |
| Programmable test voltage | 250 V to 10,000 V in 50 V or 100 V steps | Users Manual, PN 3593019 |
| Resistance measurement | 200 kΩ to 2 TΩ | Users Manual, PN 3593019 |
| Ramp mode | 100 V per second | Users Manual, PN 3593019 |
| Safety category | CAT III 1000 V; CAT IV 600 V | Users Manual, PN 3593019 |
| Input overload protection | 1000 V ac | Users Manual, PN 3593019 |
| Battery | 12 V lead-acid rechargeable, 2.6 Ah; auto shutoff after 30 minutes of inactivity | Users Manual, PN 3593019 |
| Charger input | 85 V to 250 V ac, 50/60 Hz, 20 VA | Users Manual, PN 3593019 |
| Dimensions and weight | 170 x 242 x 330 mm; 3.6 kg (7.94 lb) | Users Manual, PN 3593019 |
| Operating temperature and altitude | -20 °C to 50 °C; altitude 2000 m | Users Manual, PN 3593019 |
| Ingress rating | IP40 | Users Manual, PN 3593019 |
Safe use before you connect it
The Quick Reference Guide tells you to read the Users Manual before using the tester, and the manual opens with an XW warning to read the safety information before use. The points below come from those documents.
- Before and after each measurement, confirm that the tester does not indicate the presence of hazardous voltage, as the manual’s warning says.
- Wait until any charged capacitance in the equipment is fully discharged. The manual gives this as a condition before you finish the test.
- Use accessories with the rating the manual specifies. It describes accessories rated 1000 V CAT III or 600 V CAT IV as the ones intended for hands-free use during testing.
High-voltage insulation work belongs to trained personnel. Any work on energized panels or service equipment belongs to a licensed electrician.
1550C or 1555: what to check before you buy
- Check the 10,000 V preset. The manual marks the 10,000 V preset as 1555 only. If you need that test voltage, confirm the model number before you buy.
- Check the rating for your equipment. The tester’s category does not replace the rating of the equipment you are working on, so compare both before you connect.
- Plan for the weight and the case. At 3.6 kg, the 1555 is a bench or cart instrument, not a pocket tool.
- Get the right manual revision. The Users Manual and the Quick Reference Guide carry an April 2010 date, with Rev. 1, 3/18 on some copies. Use the current Fluke revision for your work.
How we chose
This explainer covers the 1555 because it is a separate search from the 1550C, and the model number matters for the 10,000 V preset. We opened three Fluke documents on 2026-10-27: the Users Manual (PN 3593019, April 2010) and the Quick Reference Guide (PN 3592822, April 2010 Rev. 1, 3/18), both hosted by Fluke-Direct as third-party copies, and the 1550C/1555 Calibration Manual (September 2010 Rev. 2, 6/20) hosted by Fluke. We used only the figures printed in those documents. We did not use Amazon, retailer pages, Wikipedia or forums for any figure.
What we could not verify
The three documents do not give current pricing, availability, or a comparison with other insulation testers. We did not open the 1555 safety sheet, so any safety detail that appears only on that sheet is not covered here. The Fluke-Direct copies are third-party hosting; the calibration manual is written for service personnel and does not describe everyday operation.
Mistakes to avoid
- Assuming the 1550C has the same 10,000 V preset. The manual marks that preset as 1555 only.
- Using the tester to check for voltage. The manual warns that it does not indicate hazardous voltage.
- Disconnecting equipment before the charged capacitance is discharged, which the manual warns against.
- Treating the category rating as a substitute for the rating of the equipment under test.
FAQ
Is the Fluke 1555 a multimeter?
No. The manual describes it as an insulation resistance tester. It applies a test voltage and reads resistance, and the documents we opened do not describe it as a general voltage or current meter.
What is the highest test voltage on the 1555?
The manual lists 10,000 V as a preset test voltage on the 1555, and it gives a programmable range from 250 V to 10,000 V in 50 V or 100 V steps. The 10,000 V preset is marked 1555 only.
What do PI and DAR mean?
The manual lists both as functions. The polarization index (PI) and dielectric absorption ratio (DAR) are readings taken over time that show how insulation resistance changes during a test. The manual includes sections on each, so read those before you rely on the values.
Does the 1555 run on batteries?
The manual describes a 12 V lead-acid rechargeable battery rated at 2.6 Ah and a charger input of 85 V to 250 V ac, 50/60 Hz. It also has an auto shutoff after 30 minutes of inactivity.
What is the category rating?
The printed ratings are CAT III 1000 V and CAT IV 600 V. The manual also states compliance with EN 61557 and EN 61010-1. Read the category as the environment limit, and do not assume it covers every accessory or circuit.
Bottom line
The Fluke 1555 is a specialist insulation tester with a 10,000 V preset that the manual ties to the 1555 model. Confirm the model number, read the warnings, and treat it as a tool for trained operators on high-voltage equipment.
Related guides
- What Is a CAT Rating on a Multimeter explains the category numbers used in the ratings above.
- How to Read Multimeter Symbols and Dial Positions covers the symbols on general meters, which the 1555 does not use.
- Best Multimeters for Electricians covers general meters for electrical work.
Sources
- Fluke Corporation, “1550C/1555 Insulation Tester Users Manual”, PN 3593019, April 2010. Third-party copy hosted by Fluke-Direct: https://www.fluke-direct.com/pdfs/cache/www.fluke-direct.com/1550c-series/manual/1550c-series-manual.pdf. Opened 2026-10-27.
- Fluke Corporation, “1550C/1555 Insulation Tester Quick Reference Guide”, PN 3592822, April 2010 Rev. 1, 3/18. Third-party copy hosted by Fluke-Direct: https://www.fluke-direct.com/pdfs/cache/www.fluke-direct.com/1550c-kit/quick-start-guide/1550c-kit-quick-start-guide.pdf. Opened 2026-10-27.
- Fluke Corporation, “1550C/1555 Insulation Tester Calibration Manual”, September 2010 Rev. 2, 6/20. Fluke-hosted: https://media.fluke.com/51ac6425-f238-42a8-8980-b10800c0fc6c_original%20file.pdf. Opened 2026-10-27.
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