Following on from the Flir and Chauvin Arnoux units, I decided to take a look at what Fluke offered and how it would compare to the Keysight and Megger units that I have also reviewed.


Megger Road Test Review

Keysight U1461A Fault

Chauvin Arnoux CA6526 Review

Flir IM75 Review


Fluke Insulation Testers

There are essentially three meters available from Fluke that are in the format I am interested in. The Fluke 1503 is their basic offering and does not offer any download capability and was not of much interest to me. The 1507 is their higher specification insulation tester offering insulation testing up to 10GOhms and a 200mA earth continuity test current. The 1587 is their insulation multimeter, but only offers up to 2GOhm insulation resistance testing. It does, however, offer wireless connectivity to iPad or iPhone using the Fluke Connect App.


Although the 1507 offers a higher insulation resistance value than the 1587FC, closer review of the manuals indicates that this is only at the 1kV range. At the 500V range, both units will only measure up to 500MOhm. Based on this, I chose the 1587FC as I wanted to see how the Fluke Connect application worked, and also decided it was time for an insulation multimeter for direct comparison to the Keysight instrument.


1587FC Functional Comparison

Functionally, the 1587FC compares reasonably well to the Keysight unit and for only 60% of the price. However, it does lack variable test voltage and ramp test functions. It also lacks local memory to save readings, relying completely on the wireless connection to an iPad or iPhone.


Technically, it also fails to reach the specifications of the Keysight unit, insulation ranges are definitely lower, the current and resistance ranges are slightly lower and the temperature range is significantly lower. Voltage wise, the Fluke matches the Keysight and capacitance measurements see a much wider range on the Fluke than the Keysight.

15687FC Technical Comparison

1587FC Physical Comparison

Physically, the Fluke is a little shorter and thinner than the Keysight and Megger units. It sits reasonably comfortably in the hand, but lacks the ergonomics of the Megger unit. Visually, the first thing that springs out at me is that the connection jacks for the insulation resistance measurement are on the left hand side of the meter. The top one is a unique jack just for the positive connection for the insulation test, but the bottom one is a shared jack acting as the negative for the insulation test and the positive for the current measurement. This takes some getting used to, and to be honest I am not comfortable with it, mixing voltage and current measurements can lead to dangerous scenarios in the high power electrical world, and it is something that we go to lengths to avoid. Having a meter with this kind of setup seems to me, to give the potential for costly errors.

1587FC input jacks


1587FC Contents


1587FC Packaging Box Contents 1587FC Box Contents Remved

The 1587FC comes in a black hard plastic case, with the Fluke logo on the lid, the case is covered with a cardboard advertisement sleeve. Opened up, the meter and leads arrived packaged in separate plastic bags. Emptied out, reveals the full list of contents to be the meter, a set of silicone red and black test leads accompanied with red and black probes and crocodile clips. A temperature probe and remote trigger probe complete the items to use with the meter.


Paperwork wise, for me there is a lack of a calibration certificate, instead there is a quick reference guide, a download guide card for the manuals and software, a safety booklet, a CD ROM containing the manual for the meter, a paper supplement for the manual and finally a Chinese market notice. The plastic case contains a guide pocket in the lid where all of these can be neatly stored and carried around with the meter.


This leaves three large open cut outs to house the meter and the leads. It gives plenty of room for storage but also allows for components to become mixed together very easily and rattle around. I am aware that the 1587FC is available in optional kits along with a current clamp and phase rotation meter, so I presume the case is moulded to allow these extra items to be added. Without them, I see the need for tool foam to be added to allow the accessories to be stored more securely.


Contents in box


One element missing for me is the lack of a calibration certificate for the instrument. However, as with the majority of Fluke instrumentation, a service manual is available for download from Fluke that contains the performance checks and calibration procedure. The performance checks are quite extensive and interestingly for me, contain a procedure to test the operation of the test circuit discharge function. This is something that I have not seen in a calibration procedure for an insulation tester before, and I must say that I do like it.


As Fluke go to the trouble of providing the details of the tests to be carried out, it seemed rude not to use them.



{tabbedtable} Tab LabelTab Content

Voltage Tests

These tests are conducted on the AC, AC Low Pass Filter, DC and DC mV ranges of the instrument.


DMM Voltage Tests

No real problems experienced with these tests. It can be seen that at 50 / 60Hz, the meter readings are very accurate. Accuracy decreases as the frequency of the input is increased and accuracy is further diminished when the low pass filter is applied to the AC voltage measurements.


DC mV measurement AC Voltage measurement 255Hz frequency measurement


Frequency measurements were checked using a sine wave generator and proved to be very accurate.


Current Tests

These test the AC and DC mA functions.


Current Measurments

No problems with these results, excellent accuracy on the DC mA function with the AC mA showing a bit of difference from the applied values. This would be normal behaviour for any handheld digital multimeter.


DC mA measurement

DC uA measurement

Resistance /  Capacitance

Resistance and Capacitance Tests

These measurements look at the accuracy of the resistance, capacitance, diode and temperature functions and verifies the operation of the continuity buzzer.

Resistance measurements

The zero ohms tests shows a deviation from actual, coupled together with lead resistance and the lack of a null function means that the meter is not the most accurate at low ohms and doesn't lend itself to winding resistance measurements very well.


6MOhm measurement


The 8mF capacitance measurement was fudged as I did not have an 8mF capacitor, so created a capacitor bank to get the right value. This was verified with another meter, but is obviously subject to the accuracy of that instrument.


4.7mF capacitor measurement


Temperature measurement was a little out, this was measured using the actual K-Type thermocouple supplied and not by simulating the mV input into the meter.

Insulation Resistance

Insulation Resistance Tests


These tests verify the resistance reading values, output voltage levels and current source level across the various ranges. Prior to any tests carried out enthuse functions, the resistance of the discharge circuit is verified along with the voltage detection cutout.


Discharge Circuit Test Procedure




Insulation Resistance Measurements


Accuracy levels are reasonable for an insulation tester. The lower resolution, in comparison to other testers looked at, impacts on the tolerance results for lower resistance values measured.


1.7GOhm measurement short circuit current measurement


Voltage outputs were all within the +20% tolerance specified by Fluke and the 1mA load current tested on the 1000V range is satisfactory to the IEC standard.

Battery Tests

Battery Supply Function Tests


These few tests verify the operation of the low battery warning and cutout function for the DMM ranges and the insulation test ranges that seems to require a higher battery voltage in order to work correctly.


Battery tests


To get the low battery symbol to turn off on a DMM function, the voltage had to be taken up to 4.44V. As Fluke do not provide any tolerances for these battery level values, this slightly higher value was assumed to be acceptable.


The leads that arrive with the 1587FC are high quality. The clips are Fluke's AC285 'SureGrip' crocodile clips and have a good capacity to them. The probes are fitted with a GS38 compliant protective cap that can be removed and reveals a standard 4mm connector. It was observed that with the GS38 caps fitted, access into smaller terminals such as the SAK2.5 and SAK4 was not possible. Obviously the caps could be removed, but that defeats the safety compliance and other manufacturers' probes have been manufactured to fit into the smaller terminals. There were no issues with using the probes in circuit breakers and contactors.


As the 1587FC only goes up to 2.2GOhms at 1000V, the test leads were tested with the Megger insulation tester and, not surprisingly, the insulation resistance of them was over 200GOhms.


{gallery} 1587FC Lead Set

1587FC Lead Set

1587FC Leads and Accessories

Leads 1000V Insulation test

1587FC Lead Insulation Test

Probe does not fit in SAK4

1587FC Probes do not fit into SAK4 Terminal

Probe fits into SAK10 Terminal

1587FC Probes do fit into SAK10 Terminals

Megger Probes fit into SAK2.5 Terminal

Probes from Megger do fit into SAK2.5 Terminals

Alligator Clips on Stud Terminals

Alligator clips on M12 and M8 stud terminals


Performance Checks


Switching on the instrument the screen is clear and uncluttered For me it isn't as good as the screen on the Megger  MIT420/2MIT420/2 and even with the backlight on the Fluke just doesn't display the same crisp display that the Megger does I do find the screen on the Fluke just as easy to use as the Keysight OLED display


Screen contrast Screen backlight


The same set of performance checks carried out on the other insulation testers were also carried out on the Fluke 1587FC, starting with the basic insulation open and short circuit output checks.


Open circuit tests

Short circuit tests

1mA load tests

No surprises with the results, voltage outputs are not quite as precise as the Keysight or Megger but are better at the higher voltages than the Chauvin Arnoux and Flir units. The manufacturer allows for a +20% tolerance and the values obtained are all well within that. Short circuit output is around 1.5mA, there is a slight upward trend in the short circuit current as the output voltage increases, that shows the output regulation is not as good as the Keysight or Megger units, but again the Fluke is comparable to the Chauvin Arnoux and Flir models. 1mA output loading was maintained correctly as per the requirements of the IEC standard.


Voltage regulation of the Fluke unit was not as good as either the Keysight or the Megger, but both of these models appear to be the gold standard for this aspect and in reality the Fluke unit has a similar regulation to the majority of other 1kV insulation testers.


500V output voltage data 500V output voltage plot

Battery wise, the Fluke utilises four AA sized batteries against the more common six AA batteries seen in other units. There is no voltage level displayed on the screen. The low battery symbol cut in at 4.00V and the meter then shutdown at 3.50V. The Fluke uses up 42% of battery life in comparison to the other units that only used up 22 to 36% of the battery before cutting out. A win for the Fluke.


Battery voltage data Battery usage comparison

The load each function placed on the battery was then measured.

Battery load measurement Battery load data

Highest loading on the battery was during a 1mA load test on the insulation testing function. At 0.815W load, this is lower than the other units that all take around 1W during this test. The wireless function also drew quite a low load. The backlight load is typical compared to other units.


The next set of tests centred around the accuracy of the insulation testing function. Due to the low maximum insulation value, only 91 tests could be performed, against the 200 tests for the Keysignt, Megger and Chauvin Arnoux units. The number of tests for the Fluke is actually lower than the reduced 100 set of tests for the Flir IM75 insulation tester.


Insulation Test Data

Insulation Test Plot Average Accuracy Comparison

As with all the testers, the accuracy measured far exceeded the manufacturer's specifications for all of the ranges. With the Fluke, there was a fair amount of deviation noticed between the different test voltages, not seen on other insulation testers. Overall, the accuracy over the 91 tests averaged out to a very respectable -0.13%.


Motor Simulator Tests


The first test carried out on the winding simulator is the winding resistance. This is a fairly low resistance, nominally 1.17 Ohms to 3.50 Ohms depending upon the link configuration. When conducting these tests with the Fluke, there were two issues that immediately came to light. The first, is that there does not appear to be anyway to zero the leads on the meter or create a measurement offset. The second, is the lack of resolution of the resistance range, limited to one decimal place at these low values. Both of these can impact the measurements made on the winding resistance values.


Winding resistance measurements

As can be seen, from the results above, the Fluke shows the worst out of tolerance readings for any of the instruments tested to date. In some respects, this could be considered as not much of an issue, as the main aspect of this test is to ensure that the windings are balanced. It is not very often that a winding resistance value is available for motors, but if it is, it is likely that I would use another test instrument in preference to this Fluke Insulation Tester. It should also be noted that this is a standard resistance test feature and is not a 200mA test current as per the IEC recommendations for earth bond tests. This facility however, is offered on the 1507 instrument.


The 1587FC in insulation test mode offers an additional smoothing function. This can be a useful function when testing at higher voltages with windings that have high insulation resistance in the GOhms range. It did not seem to have any effect or benefit when the winding simulator was being tested, and I suspect that with a 500MOhm limit on the 500V test and 2.2GOhms on the 1000V range, the smoothing will never be that useful a function.


The lower resolution of the Fluke is also present on the insulation test ranges, but its effect is less of an issue. The DAR value recorded by the instrument is similar in comparison to the other instruments and the PI value is a little lower, but not at a value that would represent any issues. The plot of the PI test data, shows how well the data measured by the Fluke instrument matches the Keysight and Megger instruments.


Delta Winding PI Test Data Delta Winding PI Data Plot

The simulator was reconfigured into star winding connection and the polarisation index test repeated using the Fluke Connect App to record the data transmitted from the instrument. Using the App requires you to be signed into Fluke's cloud system. The main menu contains some locked out options that require a subscription fee, but basic readings and reports can be made without this.

Selecting the 'Capture Measurements' from the 'Measurements' sub menu brings up a list of instruments available for connection. The instrument connected wirelessly to the iPad without any issue, it was automatically found by the App without any need to pair the instrument to the iPad through the system settings screens.


Selecting the instrument takes it straight to the measurement capture screen that varies depending upon the function selected on the meter. The app does not allow any control over the meter, it merely becomes a remote screen to view and save readings.


{gallery} Fluke Connect App

Fluke Connect App Main Screen

Fluke Connect App Main Screen

Measurements Menu

Measurements Menu

Instrument Selection Menu

Instrument Selection Menu

Insulation Measurement Graph

Insulation Measurement Graph

Measurement Reading

Measurement Reading

Reading Export Options

Measurement Export Options

It was noted that after an insulation resistance measurement was stopped, the iPad lost the actual voltage reading, so this was never saved as part of the reading or transmitted in the saved data, only the resistance reading, ratio and the test range were saved.


Saved readings can be exported via email in one of four formats, only one format at a time can be selected. For an insulation measurement, the app saved three to four readings per second. For me, this is excessive, for a DAR reading over 250 measurement values are recorded in the Excel file, for a PI reading this increased to over 2200. This means that to get a sensible data table to enter into a report, a bit of Excel data manipulation is required.


The end result below, was very close to a manually recorded PI test with the 1587FC However, due to the time taken for the data manipulation, there was no real benefit from using the app over the manual method. The problem with using the manual method with the 1587FC is that it does not have its own timing function, therefore the old routine with an external stopwatch would be required.


Excel File for PI Test



Motor Tests


Back in the motor store at my favourite 90kW motor, it was time to see how the 1587FC would perform at the terminals of a real motor. First test a winding balance check using the resistance function of the meter.


Motor winding resistance test


No real problems found with taking the readings, as expected the meter read high against the other instruments due to the lack of resolution on this function and the inability to zero the leads. When measured with the Keysight, the phase winding resistance was circa 0.055Ohms, but the Keysight has more resolution on the resistance range, a 200mA test current and a lead zeroing function. At the end of the day, the readings were all balanced when measured with the Fluke, so the test can be seen as successful in my opinion.


One minute insulation resistance tests were then carried out at both the 500V and 1000V ranges on the 1587FC. Initially, I made a slight error taking the measurement - using the wrong input jacks on the meter, it took me a little longer to realise as I was expecting the meter to go over-range on the 500V setting. On this occasion, there is no immediate safety issue, as I used the voltage input jacks and the motor terminals are obviously dead anyway. An issue could have occurred if the motor did have a fault, as I would have missed it and could have installed a faulty motor. The error is nothing more than down to me used to using the voltage terminals of an instrument to carry out an insulation test.


Insulation test wrong connections Insulation test right connections 500V DAR Error

With the correct terminations on the meter utilised, the test was repeated. As seen in the second picture the meter goes to over-range during the test and then at the end of the 1 minute produced an error message and cannot display a DAR value. This is because the motor has an insulation resistance of circa 4GOhm, which is above the range of the 1587FC.


The same outcome was seen when the 1587FC was switched to the 1000V test range. Although this extends the reading capability of the 1587FC up to 2GOhms, this is still inadequate for this particular motor, and the same error message was seen.


1000V DAR Error message


Meter build quality


With all the testing completed, I decided to take a look inside the 1587FC to see what the build quality was like, and it definitely doesn't dissapoint.


The meter is housed in a detachable rubber boot for impact protection, that is prized off to reveal the battery cover. This is secured in place with a plastic twist lock, turned 180 degrees unlocks the cover and allows it to be removed to reveal the batteries and fuse. Four Energiser AA batteries are supplied and a 440mA HRC fuse with a 10kA breaking capacity. The use of such a high rating fuse is essential for the type of apparatus I work on. Some manufacturers fit fuses of lower breaking capacity in the mA function circuits, but it isn't about the rating of the meter, it is about the fault current capable of flowing from the circuit under test.


Four self tapping screws hold the case together and once removed the back cover can be prised off to gain access to the PCB. The back cover contains spring loaded contacts to transfer the battery voltage onto the PCB - no chance of getting any wires trapped during reassembly.


The quality then starts to show. The board is clean and well assembled. The input circuit is well laid out with space around the components that could be subjected to high voltage. The contacts for the input jacks are soldered directly onto the PCB, so may develop a weakness over time if it is subjected to rough treatment.


A small EMF shield can be removed to reveal a resistor divider network and an element of the control circuitry. A single screw holds the PCB in place in the front case. Neither the LCD screen or the function switch contact block need to be removed to allow the front case to be separated from the PCB, but they are only held in place via plastic clips, so can be gently removed.


{gallery} 1587FC Build Quality

Battery back cover removed

Rubber boot and battery cover removed

Rear Case removed

Rear case removed

Input circuit, jacks and fuse

Input jacks, fuse and components

High voltage circuit

High voltage generator circuit

Internal EMF Shield removed

Internal EMF shield removed

PCB removed from case

PCB board removed from case

LCD removed

LCD removed from board

Input jacks

Input jacks and isolation slots

Input circuit PTCs

PTCs, fuse carrier and input jacks

Main chipset

Main processor and wireless module

With the board removed from the case, the connection method for the input jacks can be clearly seen and for me, is probably the one weak area in the meter design. Soldered direct onto the PCB in this manner they will be subject to the force of pushing the test leads into the sockets.


The main controller chip sits up towards the top of the PCB just below the wireless module and buzzer. The main chip appears to be a Texas Instruments M430F6483 controller.


Overall this is a really neat tidy build from Fluke, it comes together very easily and was reassembled without any issue - always a sign of a good quality instrument.




The Fluke 1587FC is a really nice high quality instrument. Build quality is excellent and it comes with some superb accessories. I guess it is what you would expect from Fluke. Unfortunately for me the implementation of the insulation testing functions do not match my needs and I think they fall short of the requirements for the insulation systems on modern motors. Fluke are advertising this with a number of packages aimed at motor maintenance and that is traditionally what the DAR and PI ratios are used for. But they aren't much use when the meter goes into error and cannot produce a reading. Insulation testing offers the most benefits when used as a historical trending tool, but with the low insulation range capability, there is a strong likelihood that trends cannot be established.


The software side has been implemented quite well, although it is limited by not having any memory within the meter itself. This means that you always need an iPad or iPhone with you if you wish to record the data. One nice touch I did find, was that my iPad mini fitted nicely into the large compartment of the case and could easily be carried around with the instrument. The App appears to have a basic set of functions and then a further set of functions that require a subscription license. Whilst four readings per second may be justified for voltage or current monitoring, it is just too much for a DAR or PI test, and for me the functionality could be improved by reducing the amount of data collected.


For the Fluke 1587FC to be a serious contender for me, the low insulation range for the 500V test voltage needs to be addressed, a variable test voltage function adding and the GS38 caps need to be redesigned to allow access into smaller type terminals. The benefit of the smoothing options needs to be reviewed, for me it would be better to replace this with a 200mA earth bond resistance test. I would also need to have a good think about the input jack assignment, mixing the current input jack with voltage test functions for me is the wrong way to go, and on several occasions I was caught out with not having the leads in the right inputs.


Unfortunately it looks like this instrument will go into the growing pile of instruments that aren't worth taking up to the generator rotor to see how they would perform.


Fluke however have redeemed themselves slightly, for as I was reviewing this meter, I learned that they have made the IR3000FC wireless adapter for the 1555C insulation tester I have available for the UK market. I will need to evaluate the device to see how it functions with the software, as if it has the same short-comings found whilst reviewing the 1587FC, it may not be the best solution for testing the generator rotors.


IR3000FC Adapter


I did try and make some videos using the 1587FC, but they have not come out very well, so I have left them out. I do feel however, that they do more justice to the use of the unit, especially showing the functionality of the software, so I will try and remake the videos and upload them at some point.