Fluke 1535 Insulation Tester Review: Test Voltages, Ranges and CAT IV Rating
As an Amazon Associate we earn from qualifying purchases.
The person typing fluke 1535 wants to know what the Fluke 1535 is, what test voltages and resistance range it covers, whether its safety rating fits their work, and how it compares with the rest of the Fluke insulation tester line. The Fluke 1535 is a 2500 V insulation resistance tester, also called a megohmmeter. It is the model without the 1537’s extra features. This review uses only the manufacturer product page and two Fluke Learn guides that we opened. It describes only what the sources state, and it marks every point that they do not settle.
Quick answer
- Model: the manufacturer page names it “Fluke 1535 2500V Insulation Tester”.
- Test voltages: 250 V, 500 V, 1000 V and 2500 V, user-selectable.
- Resistance range: up to 500 GΩ on the 2500 V setting, with the top decade listed at 20 % accuracy.
- Safety rating: CAT IV 600 V overvoltage category, with IEC 61010-1 cited on the page.
- Not confirmed for this model: the warranty term. The page lists the extended 3-year warranty only with the 1537.
Who this tester is for
An insulation resistance tester applies a high DC voltage to a circuit, cable, motor winding or transformer and measures how much current leaks through the insulation. The result is a resistance reading. Electricians, maintenance technicians and motor shops use these readings to check whether insulation has degraded, is wet, or is contaminated. A tester with a 2500 V setting fits work on higher-voltage equipment, where a 500 V or 1000 V tester may not be enough to reveal a weak spot.
If your work is limited to household outlets, lamp cords or low-voltage wiring, a lower-voltage megger is usually the more practical choice. The sections below explain the numbers so you can decide whether the 1535 fits your equipment.
Specifications from the manufacturer page
The Fluke product page for the 1535 and 1537 gives one shared specification table for the series. The page labels the 1537-only features clearly, so the values below are the ones the page presents for the 1535 or for both models. Where the page does not separate the two models, we say so.
| Specification | Stated value | Found on |
|---|---|---|
| Designation | Fluke 1535 (the 2500 V insulation tester) | Fluke product page (en-us and en-gb) |
| Test voltages | 250 V, 500 V, 1000 V, 2500 V, user-selectable | Fluke product page |
| Fine voltage steps | Not on the 1535. The page lists 100 V fine-tuning as a 1537 feature. | Fluke product page |
| Insulation resistance range | Up to 500 GΩ | Fluke product page |
| Accuracy at 2500 V, 0.50 GΩ to 50.0 GΩ | 5 % | Fluke product page |
| Accuracy at 2500 V, 50 GΩ to 500 GΩ | 20 % (resolution 5 GΩ) | Fluke product page |
| Above 500 GΩ | Listed as unspecified | Fluke product page |
| Test voltage accuracy | −0 %, +10 % at 1 mA load; ±(3 % + 3 V) for the insulation test voltage | Fluke product page |
| Short-circuit current | Greater than 2 mA (the 1537 is listed at greater than 5 mA) | Fluke product page |
| Safety category | CAT IV 600 V, IEC 61010-1 | Fluke product page |
| Power | 8 AA alkaline cells, IEC LR6 | Fluke product page |
| Weight | 1.3 kg | Fluke product page |
| Ingress protection | IP40 | Fluke product page |
| Operating temperature | −10 °C to +50 °C | Fluke product page |
Two lines in the table need a careful read. First, the 500 GΩ top of the range is at 20 % accuracy in its decade, so a reading near 500 GΩ is an estimate, not a precise value. Second, the page lists the 5 % accuracy only from 0.50 GΩ up to 50.0 GΩ. Readings below that span carry the accuracy figures printed for their own rows in the table, and some of those rows are unspecified on the page. Check the printed table before relying on a reading in a low range.
What the numbers mean in practice
Choosing a test voltage
A higher test voltage stresses insulation more and can reveal a weakness that a lower voltage misses. The 1535 offers four settings, so you can match the test to the equipment rating. A common approach from maintenance practice is to use a voltage that suits the equipment’s rated voltage, and to record the voltage used with every reading, because a reading taken at 500 V cannot be compared directly with one taken at 2500 V. The Fluke Learn guide on insulation resistance testing recommends recording the test voltage, duration and temperature with each reading so that results can be trended over time.
Reading the resistance
Insulation resistance readings change with time and temperature. The Fluke Learn guide explains two timed ratios that many technicians use. The polarization index compares a reading at about 10 minutes with a reading at about 1 minute. The dielectric absorption ratio compares a 60-second reading with a 30-second reading. The guide also describes temperature correction: resistance readings change by roughly half for every 10 °C of difference from a baseline temperature. Our reading of the guide is that a stated baseline, usually 40 °C under IEEE 43 as the guide notes, makes historical comparisons meaningful. Confirm the baseline your own standard requires before you record a result.
The 1535 page does not describe timed ratio functions or temperature compensation for this model. Those points come from the general guide, not from a feature list on the product page. If you need a ratio function built into the meter, check the manual for your exact unit.
Safety rating
The CAT IV 600 V rating tells you the tester is intended for measurements at the origin of an installation, such as a service entrance, where fault currents can be high. It does not mean the tester is safe on any circuit up to 600 V. Always de-energize and lock out equipment before connecting leads when the procedure requires it. The Fluke Learn article on insulation multimeters makes the same point: the de-energized state is the safer starting point, and personnel should wear appropriate protective equipment before opening enclosures to take live measurements.
Power and portability
The 1535 runs on eight AA alkaline cells, which is a common and widely stocked battery choice. The page quotes a weight of 1.3 kg. That is heavier than a handheld multimeter, so plan for it if you carry the tester on a long route. The page does not state a battery life figure for the 1535 that we could read, so we do not give one.
How we chose this model for a review
We wrote this review because the search term names one exact model. The criteria were simple. The model has to appear by its exact name on a manufacturer page. Its core specifications, meaning the test voltages, the resistance range, the accuracy rows and the safety rating, have to be readable on that page. And we need at least three readable sources that we opened. For this model we opened two Fluke product page versions and two Fluke Learn guides, which gives four readable sources in total. The two Learn guides are general background, not model specifications. The Fluke PDF datasheets for this model returned as unreadable binary files, so we did not count them.
What we could not verify
- Warranty for the 1535. The page attaches the extended 3-year warranty to the 1537 only. The warranty term for the 1535 is not stated in any source we could read.
- Resistance above 500 GΩ. The table lists this range as unspecified, so no accuracy figure applies there.
- Accuracy at the lower test voltages. The table shows the 5 % and 20 % rows we quoted for the 2500 V setting. We could not confirm the full accuracy grid for 250 V, 500 V and 1000 V from a readable source.
- Battery life. We found no readable battery life figure for this model.
- Shared versus model-specific figures. The page presents one table for the series. Where a figure is not labeled for the 1535, we treat it as shared and say so. The short-circuit current is the one value the page states separately for each model.
- Accessories and leads. The page does not list the included test leads or the case contents in a form we could read, so we do not describe them.
- Field performance. No source we opened describes how this model performs in use, and we do not claim it.
Where to buy and the current listing
The link below points to the model named in this review. Check that the product title matches the name given above, because similar Fluke insulation testers have close names.
- Fluke 1535 Insulation Tester: View on Amazon
Related reading on this site
If you are still choosing a tester, the guide to insulation resistance testers for motors and wiring covers the general decision, and our overview of insulation resistance test equipment lists the main categories. Both are general guides, not reviews of this model.
FAQ
Is the Fluke 1535 the same as the 1537?
No. The page presents the 1537 as the model with the extra features, including 100 V fine-tuning of the test voltage, a timer of 0 to 99 minutes, AC and DC voltage measurement up to 600 V, a short-circuit current above 5 mA, and an extended 3-year warranty. The 1535 has the core insulation test functions with four preset voltages.
What test voltages does the Fluke 1535 offer?
The page lists 250 V, 500 V, 1000 V and 2500 V as user-selectable settings for the 1535.
What is the highest resistance the Fluke 1535 can measure?
The page says up to 500 GΩ. The top decade is at 20 % accuracy, and readings above 500 GΩ are listed as unspecified.
What is the CAT rating of the Fluke 1535?
The page lists CAT IV 600 V. Use the rating only as a guide to where the tester is designed to be used, and follow the manual and your site procedures for each job.
What battery does the Fluke 1535 use?
It takes eight AA alkaline cells, IEC LR6, according to the manufacturer page.
Does the Fluke 1535 come with a warranty?
The sources we opened do not state a warranty term for this model. The extended 3-year warranty appears only in the 1537 feature list. Check the warranty card or documentation included with the unit you buy.
A practical workflow for the readings
The sources describe a sequence that works well with any megohmmeter, and it applies to the 1535 as well. Start with the equipment de-energized and locked out according to your site rules. Record the equipment identifier, the ambient temperature, the test voltage and the time of day before you start. Apply the chosen test voltage and read the value at fixed intervals, for example at 30 seconds and at 60 seconds, so that you have points for a ratio calculation. If your procedure calls for a longer hold, continue to the interval it specifies, usually around 10 minutes for the polarization index. Discharge the equipment fully after the test before you disconnect the leads, because stored charge can remain in long cable runs and windings.
Keep the raw readings, not just a pass or fail mark. The Fluke Learn guide makes the point that a trend across several tests reveals degradation that a single reading can hide. A reading that drops steadily over the hold, or that stays flat at a low value, tells a different story from a reading that climbs and levels off. Interpreting those shapes is part of the job, and the general guides cover the logic. The 1535 page does not provide pass or fail thresholds, so set the acceptance values from your equipment standard or the manufacturer of the equipment under test.
Plan for the temperature. The guide’s correction approach means a reading taken on a cold winter morning and one taken on a hot afternoon can differ a lot even on the same circuit. Note the temperature with the value, and correct to a common baseline before you compare results across seasons. This step is more important than the choice of meter for most trend work.
Bottom line
The Fluke 1535 is a 2500 V insulation resistance tester with four preset test voltages, a resistance range up to 500 GΩ, and a CAT IV 600 V rating, according to the manufacturer page. Choose it when your work needs a 2500 V test and you accept the accuracy limits printed for the top decade. If you need the 100 V fine steps, the timer or the 600 V voltage measurement, the page points you to the 1537 instead.
Sources
- Fluke, “Fluke 1535/1537: Insulation Resistance Tester & Megohmmeter”, product page, en-us. https://www.fluke.com/en-us/product/electrical-testing/insulation-testers/fluke-1535-1537 (opened 2026-10-28)
- Fluke, “Fluke 1535/1537: Insulation Resistance Tester & Megohmmeter”, product page, en-gb. https://www.fluke.com/en-gb/product/electrical-testing/insulation-testers/fluke-1535-1537 (opened 2026-10-28)
- Fluke Learn, “Guide to Insulation Resistance Testing”. https://www.fluke.com/en-us/learn/blog/insulation-testers/use-insulation-resistance-testing-data-to-avert-unexpected-downtime (opened 2026-10-28)
- Fluke Learn, “What is an Insulation Multimeter?”. https://www.fluke.com/en-us/learn/blog/insulation-testers/what-is-an-insulation-multimeter (opened 2026-10-28)
