I decided it was time for me to take a look at another insulation tester. This particular one is from Hioki, the IR4058-20. Previous Insulation Testers Reviewed;


Keysight Insulation Multimeter Failure


Megger MIT420/2 Road Test


Chauvin Arnoux CA6526 Insulation Tester Review


Flir IM75 Insulation Tester Review


Extech MG302 Insulation Tester Review


Di-LOG DL9307 Insulation Tester Review


RS Pro RS-9985 Insulation Tester Review


RS Pro IIT1500 Insulation Tester Review


Uni-T UT505A Insulation Tester Review


Sonel MIC-30 Insulation Tester Review


GMC MetraHit Coil Motor Testing Multimeter Review


Brymen BM877 Insulation Multimeter Review


I am aware of Hioki, as an instrument manufacturer, as I have used their battery impedance tester for many years now. It has always been a reliable instrument and served me well over the years, so I was interested to take a look at one of their insulation testers. Hioki have a range of analogue and digital insulation testers.


The analogue range goes up to 2 GOhm at 1000V and the digital range goes up to 4 GOhm also at 1000V. Some of the testers also offer a 200 mA continuity test for earth connections. They also offer two specific insulation testers, one aimed at solar installations and another that can test at up to 5 kV.


{gallery} Hioki Insulation Tester Range

Hioki Analogue Range

Hioki range of analogue insulation testers

Hioki Digital Insulation Tester Range

Hioki range of digital insulation testers

Hioki PV and HV Insulation Testers

Hioki PV and HV insulation testers

Except for the high voltage tester, all the insulation testers follow a similar physical format, being built into a compact case that houses the meter and all the accessories. None of the low voltage testers offer any form of diagnostics, although they do have the ability to lock the test on, but any timing required has to be done manually. The high voltage tester does offer DAR and PI ratio measurements. Only the IR4058 provides a wireless connection, via bluetooth, but this is for live transfer of readings as there is no onboard memory. This was therefore the instrument of interest to me, to see if I could manually carry out DAR and PI tests, but record the readings electronically.



Unboxing and Overview


The IR4058 arrives in a cardboard box, with a manual and safety sheet and all the accessories packaged within the instrument case. The insulation tester being housed within its own case is a different design concept to all the other insulation testers that I have reviewed to date. This makes the IR4958 a compact package, but means there is little space to add any extra accessories that may be required.


{gallery} Hioki IR4058 Kit Contents

Hioki IR4058 Manuals

Hioki IR4058 box contents

Hioki IR4058 in case

Hioki IR4058 with accessories in case

Hioki IR4058 Kit Contents

Hioki IR4058 accessories removed from case

When unpacking the accessories, the first thing observed is that only one crocodile clip is provided. For an insulation tester that can be locked on for timed tests, I just don't get this decision however, Hioki are not alone in this as Chauvin Arnoux sometimes only supply one crocodile clip. It isn't a big deal as the leads are compatible with standard 4 mm safety sockets, but when I buy an insulation tester, I want everything I need within the kit and do not expect to have to hunt around for extra accessories.

Standing the Hioki IR4058 alongside my two benchmark insulation testers shows the completely different design concept.


Hioki IR4o58 Meter Comparison


The meter doesn't really work too well when it is stood up like this and is much more user friendly when it is laid down. The display is a similar size and layout to that of the MIT420/2MIT420/2 with a curved analogue bar across the top and the digital readout below this. On the Hioki, the digital display shows the test status just above the insulation resistance readout. In comparison to the MIT420/2MIT420/2, I find the display on the IR4058 a little blotchy and not quite as crisp, that is just my personal preference.


IR4058 by MIT420


The IR4058 has a backlight that is operated manually by a blue push button underneath the display. The backlight works well and enhances the display for use in darkened environments.


IR4058 display lit up Backlight comparison


The test leads that arrive appear to be good quality. The probe tips are insulated for GS38 compliance in the UK, the insulation tip can be removed to reveal an uninsulated probe tip. However, the insulation is thin and allows access to test on 2.5 mm DIN terminals without any problems and consequently fit in all the other types of terminals I utilise. The single crocodile clip is a good size and easily grips M8 and M12 studs and nuts. The crocodile clip actually looks to be physically the same as those supplied with the Keysight U1461AU1461A, except for the Hioki branding.


The leads were tested as a bunch at 1000V using the MIT420/2MIT420/2 and read over 200 GOhm. There should be no problems with these affecting the insulation test readings on the Hioki.


{gallery} Hioki IR4058 Test Lead Set

IR4058 Croc Clip and Probe

Hioki IR4058 Crocodile Clip and Probe Tip

IR4058 Probe insulation removed

Insulation tip removed from probe

Probe in 2.5mm DIN terminal

Probe tip successfully used in 2.5 mm terminal

Probe tip in SAK4 terminal

Probe tip successfully used in SAK4 terminal

Probe tip in MCB

Probe tip successfully used in MCB terminal

Croc clip on M8 stud

Crocodile clip on M8 nut

Croc clip on M12 nut

Crocodile clip on M12 nut

Crocodile clip comparison

Hioki and Keysight crocodile clip comparison

1000V insulation test on leads

1000V insulation test on leads


Hioki also make a remote control test probe for use with the IR4058. This is not included within the kit and can be obtained as an individual lead or as part of a lead kit with a black test lead and crocodile clip. To go with the remote control test probe, an extended probe tip to give better access to screws terminals can also be obtained as a further separate item. Farnell UK do stock the extended probe tip Product LinkProduct Link however, I could not find a supplier in the UK for the actual remote control test probe.


Remote control probe Extended probe tip


The test leads plug into connections on the top of the meter housed away inside the case. I did find in use that this tended to cause the leads to fall over the display screen and block the reading and/or create a shadow over the display. Not much of a problem, it just becomes a nuisance after a while and slightly detracts from the overall usability of the instrument.

Example of lead positioning


The manual supplied is just in English and looked to be very well written. The instructions were concise, accurate and easy to follow accompanied by pictures when required.


Example of instruction manual


In comparison to the other instruments that I have looked at, the Hioki IR4058 comes in around mid-range in terms of price. There are a number of meters out there that appear to offer more functionality for a similar price. The IR4058 lacks variable and ramp voltage tests and recording of the DAR / PI ratios. It also lacks onboard memory, but does have the bluetooth connection to overcome this. It is a basic insulation tester, so only has voltage and continuity functions to add to the insulation resistance tests.


Hioki IR4058 Functional Comparison

Hioki technical comparison


Technically, the IR4058 has the five common voltage test levels for insulation testing, but the 100 V range is replaced with a 125 V, this does not pose a big problem for me as the majority of the circuits I test will be 110 V AC or 120 V DC. I have seen this 125 V range on a few other meters from the Japan / China region. The voltage range will measure to 750 V CATIII, which is adequate for insulation testing, but not up to the CATIV rating of the other major manufacturers and would no the used by me on the type of installations I work on. The continuity measurement will go up to 1000 Ohms, with a 200 mA test current up to 20 Ohms. The changeover is automatic, having only one position on the rotary switch for the continuity function. There is also a lead zero function to give better accuracy for the continuity tests.


The downside to the insulation measurements in the restriction of the measurement capability. At 1000 V test the IR4058 can go up to 4 GOhms, but this drops down to 2 GOhms at 500V and then rapidly drops off to 500 GOhms on a 250V test. As I have stated in previous blogs on insulation testers, whilst it is slightly better than a lot of other testers reviewed, this just isn't high enough a measurement capability to assess modern insulation systems, especially for timed tests. I would expect all three of these test ranges to go up to 40 to 50 GOhms.


Performance Tests


The IR4058 performed ok in the insulation resistance accuracy tests. Accuracy tended to be better around the mid-range and also in the GOhm range. The worst readings were in the kOhm range, which isn't really where an insulation tester is utilised, so the inaccuracy is less of a concern. The accuracy correlated quite well across the five different test voltages as seen in the plot below the test data.

Hioki IR4058 IR Test Data

Hioki IR4058 Test Data Plot


Having a reduced insulation testing range, the average accuracy of the IR4058 is compared across 100 tests to the other instruments and fairs quite well at -0.24%, the accuracy is similar to both the U1461AU1461A and MIT420/2MIT420/2 and is more than adequate for an insulation tester.


Hioki IR4058 average accuracy


The open circuit voltages are within 20% of the nominal values. Compared to the other instruments reviewed, they are towards the upper voltage levels seen. Remember that the 100 V range is actually 125 V nominal for the IR4058.

IR4058 open circuit voltage


The 500V regulation test shows the poor regulation in comparison to the Keysight and Megger units, but it is typical of a lot of insulation testers. Interestingly, it was observed that there was a continued very slight climb of the output voltage as the load resistance was increased.


IR4058 500V regulation data IR4058 500V regulation plot


A sharp initial spike was seen on the output voltage of the IR4058 when it was captured using an oscilloscope and high voltage probe. This was quite unusual and I have not seen such a high spike before, indicating that the output regulation could do with some improvement. The test setup for this is my usual home-brew high voltage probe with the Picoscope that has quite a high input resistance. I decided to repeat this test using a Micsig high voltage probe that has a lower input impedance of 10 MOhms.


IR4058 scope capture of output voltage


With the higher load applied to the output of the tester, the output spike was not seen and a much steadier ramp rate of the output voltage was produced. It seems that the IR4058 relies on the actual test load for some of the output voltage regulation.


10MOhm load output voltage measurement


The short circuit current should be less than 1.2 mA according to the manufacturer's specification. A very consistent set of readings was obtained from the tests, just above 1 mA.


IR4058 short circuit current


The 1 mA load measurement was also successfully measured. The current measured was just above the 1 mA required by the IEC standard with a spread of 32 uA. This puts the IR4058 in the middle of the pack when compared to all the other instruments.


IR4058 1mA load current


At a little over 2 MOhms, the discharge resistance it towards the lower values seen across the instruments reviewed, giving a relatively fast discharge of the voltage applied once the test is over.


IR4058 Discharge circuit resistance


The IR4058 uses a battery pack consisting of four AA cells to give a nominal 6 V. There is a permanent battery level indicator on display in the top left corner of the display. The level is not spread evenly across the three bars of the battery level indicator. The first bar drops off after 0.75 V with the second bar dropping of after a further 0.6 V drop and the final bar lasting for another 0.4 V.


IR4058 battery level indication

The IR4058 does not have as many functions as a lot of the other testers reviewed, so the power consumption table is a little smaller than usual. The insulation test draws the most power from the battery pack, closely followed by the 200 mA continuity test.


IR4058 battery consumption

The backlight increases the load by 62% and the wireless bluetooth modules adds a further 21% to the basic load of the instrument whilst measuring a voltage. For a further comparison I looked at the load of the bluetooth modules for the other insulation testers that have them fitted. There IR4058 does not appear to have the lowest powered bluetooth module, that goes to the Fluke, but it also does not draw the most power, as seen on the Flir IM75.


Bluetooth battery comparison


The IR4058 only used 25% of its battery pack before it cuts-out with a low battery. This is at the bottom end of the performance plot, with the better meters in this category, extracting over 50% of the battery capacity before the meter cuts-out.


Battery consumption comparison



Winding Simulator Tests


The winding simulator was used to carry out DAR, PI and resistance tests using the IR4058. As previously mentioned, the IR4058 does not have a facility for these ratios, so the timing and calculations are all done manually. In the picture, the IR4058 has been propped up to aid with reading the meter during the test. This is done with any object to hand as the IR4058 will only lay flat or stand up vertically and does not have any tilt stand. I will see how much of an issue this is later when I take the meter out into the field for some work on real motors.


Insulation test on simulator


Later on, I did find that the meter can be hinged up, after the lid is full slid underneath the base, to provide a slight tilt to the instrument. The meter is held in place by friction, but seemed to be tough enough to withstand the pressing of the buttons and operation of the switches. This function isn't mentioned anywhere in the manual.


IR4058 in tilted position


To carry out the PI tests, the IR4058 has to have the insulation. test locked on and this is achieved by flipping up the test button, a rather unique movement I have not seen on an insulation tester before. I am not sure how robust this will be, it seems to me it could get snapped off through either heavy handed use or being dropped.


IR4058 locked on


I am also unsure if the gap around the hinge is sealed to prevent dirt ingress. I will aim to find that out during the tear down.


Close up of switch


The results obtained for the polarisation index test were comparable to previous tests. It was found that the IR4058 does not display the actual test voltage during the test, it can also not be configured to show the test current, functions that both the U1461AU1461A and MIT420/2MIT420/2 have built into them.


Simulator PI Test Data


The plot depicts how well the IR4058 followed the expected test results.


PI Test plot


Winding resistance tests were also carried out Ising the simulator and too show a good set of results. The lead null facility was used during these tests and the test current was measured as 217 mA, which is acceptable. As with the vast majority of the instruments out there, the continuity measurement functions offers a reading to two decimal places.


Simulator winding test current


The test current was verified with the U1461AU1461A. Note that the reading on the IR4058 is higher than expected due to the loading of the U1461AU1461A.


Verification of test current


The removal of the 500mA fuse in the battery compartment, produces a 'Fuse' alarm on the screen when the test is activated.


Fuse location Blown Fuse indication

Fuse blown with live voltage present


Even with the fuse removed, the continuity range still detected a live voltage was present and alarmed with a red screen and flashing hazard symbol as well as displaying the blown fuse alarm, as seen above.


A point noted during the insulation testing was that the polarity of the test outputs was reversed and did not follow usual convention. Not too much of an issue for AC circuits, but if the IR4058 was utilised on DC circuits, then that may cause some problems with the tests if not understood. This is something else I did not notice mentioned in the manual.


Reverse polarity of IR4058 output



The IR4058 does have a voltage presence warning when in both continuity and insulation test functions. The screen lights up red and the hazard warning symbol is present. The voltage value is not displayed on the screen though. I also found that whilst the voltage was detected, the instrument did not lock out and when the operation button was pressed, the meter did indeed revert to insulation test mode and applied the test voltage. This could present a danger to anyone using the meter, especially if the circuit became live whilst the test was in progress.


Live voltage warning


Motor Tests


A 90 kW three phase motor was utilised for carrying out tests in the field. Winding resistance measurements were made with the motor in 'delta' configuration, followed by a one minute insulation test.


Motor test setup


Winding resistance measurements were made with the null adjustment against the leads applied. A value of 0.3 Ohms was achieved for all three measurements, the benefit of the second decimal place of the IR4058 clearly demonstrated against those testers that only have the one decimal place reading. The leads were long enough to make the connections and the crocodile clip was large enough to clip onto the motor terminals.


Winding resistance value


As the instrument does not possess any DAR or PI ratio functions, only one minute insulation tests were conducted. To aid with this, the IR4058 does record the insulation value after one minute. The initial test at 500 V did not record a value as the actual insulation reading is higher than the 2 Ohm limitation of the 500 V range.


500V IR test


On the 1000 V test range, a reading at one minute was obtained. Repeated testing at 1000 V of a motor in service goes against the advice in the IEC standard that drops the test voltage down to 500 V after the motor is installed. There are a number of insulation testers out there that can read insulation values higher than the IR4058 on a 500 V test, so the IR4058 is somewhat lacking as a motor testing device.


IR test at 1000V


Physically the motor was okay to use during the tests, it could easily be propped up to get a better viewing angle of the display. I had not worked out the tilt function offered by the lid at that time!


I did have trouble siting the IR4058 on top of the motor. Whilst the lid has ribs on it, they are made of hard plastic so did not provide any grip in this instance. With the IR4058 having a larger footprint, not much of it was in contact with the top of the motor and it was found to be unstable and very easily slid off. This is exacerbated by the bottom section of the instrument being haver than the empty compartment for the leads at the top. I feel a non-slip surface on the lid would prevent the instrument from slipping about to some extent, but the physical nature of the instrument's size means that it will likely be unstable in these scenarios.


IR4058 located on top of motor


Software Operation


The software connection via the builtin bluetooth function was of great interest to me. My primary reason was to see if I could use this as an alternative to carrying out polarisation index tests instead of manually recording the data. Hioki provide the Gennect software for both IOS and Android. These tests were conducted on the IOS version. They also provide the Gennect One (formally Gennect Cross) software for Windows based computers.


The software is currently provided free of charge and was easily downloaded from the Apple Store and loaded onto my iPad. When turned on and with bluetooth activated, the IR4058 was found automatically by the software without going through any pairing function. The software gave the option of adding a description for the device that had been found. With the device settings completed, the software reverts to its main screen showing the options available.


It then becomes clear that the Gennect software is designed for multiple types of instruments, most of which do not appear to be compatible with the IR4058 insulation tester. The two options that appeal to me are the 'General Measurement' and the 'Logging (Recording)' functions.


The General Measurement works fine with the IR4058, the instrument connected is identified and the range it is on automatically appears as it is changed on the instrument. The Gennect software does not have any control elements and relies on manual operation of the IR4058. When a measurement is made the value appears on the screen, there is a slight delay between the reading on the instrument and the reading on the iPad, but nothing significant. When the reading is complete, the Gennect software automatically saves the final value.


Gennect software options Measurement screen Logging screen


Unfortunately, when trying to use the Logging function, the third screen above is displayed, indicating that the logging function will not work with the IR4058. This stopped any notions of using the IR4058 for recording PI readings and was a huge disappointment to me. It also seems to go against the instruction manual that to me, infers that the logging function can be used with the insulation tester.


Software description for IR4058


Taking a brief look at the options available from the general measurements, all the measurements stored can be displayed from the folder option. Individual readings can be edited to add in some notes, seen in the second picture. There also exists an option to generate a PDF report based on the general measurements selected.


General measurements saved Editing a general measurement Creating a report



Build Quality


The IR4058 is relatively simple to dismantle. The battery compartment lid is held in place via one machine screw that is captivated in the lid, when removed. Removal of this lid, also gives access to the fuse for the continuity function, allowing its replacement without invalidating any calibration.


Battery compartment lid removed


The meter section is then held in place by four self tapping screws. With these removed the front face of the instrument can be lifted away. There isn't much to see on the front part of the PCB. The pads for the switch and push buttons can be seen. A moulded cover can be seen for the test switch, showing that it is protected from moisture and dirt ingress. The rotary switch for selecting the functions is an enclosed type. The detent for the switch is sprung plastic, common to many meters.


Front face of meter removed Test Switch seal


The input jacks for the instrument are fitted inside there own housing that slides into the case. The connections for the remote probe are also fitted in the same housing. This offloads any pressure of inserting the leads and protects the PCB from damage.


Input jack housing


Lifting the PCB out of the case reveals the main electronics of the IR4058, all on the one side of the PCB.


IR4058 Printed Circuit Board


The bluetooth module is located right next to the micro-controller and is a BLE113-A from Silicon Labs. The main micro-controller is the M430F4794 mixed signal micro controller from Texas Instruments.


IR4058 Main microcontroller


The micro-controller is a 16-bit device with four 16-bit analogue to digital converters and nine 8-bit digital I/O ports. An onboard 160 segment LCD driver means the display is driven directly from the controller.


Microcontroller block diagram


Input protection wise, there is the fuse of the continuity input. A single gas discharge tube and varistor, along with two PTCs protected by a rubber cover protect the voltage input and insulation test output. The input protection is to CAT III to 600V, I could not determine if that has been tested independently.


Input protection


The high voltage transformer is driven by an N-Chanel MOSFET type 050N10. The function selection relay can be seen to the left of the transformer.


HV Transformer and MOSFET


The voltage dropper relay for the input circuit of the meter appears to be made from a series of individual SMD resistors leading into the function selection relay. This is an unusual approach for higher end insulation testers, then tend to adopt a single high value film resistor.


Dropper resistor


The smaller ICs around the main micro-controller are a mixture of multiplexers and amplifiers.


PCB overview


The overall build is very tidy. The PCB is clean with no signs of flux or solder residue. There was no signs of debris inside the plastic case.




Overall I have to say I am a little disappointed with Hioki and this instrument. It appears to be at the upper end of their 1000 V insulation tester offerings, but compared to a lot of their competitors, it lacks quite a bit of functionality and carries a significant cost to it.


The build of this insulation tester is certainly of good quality. I like that it is built into the case, although this makes adding accessories a bit more awkward. Given the asking price for this instrument, I would have thought Hioki could have included the second crocodile clip along with the remote probe. The probes and leads that are supplied are good quality and the crocodile clip is of ample size to cover a wide range of stud terminals.


I cannot fault the continuity function, it is accurate and both the lead zeroing and comparator functions work well. The insulation testing functions have problems. A voltage warning function is built into to alarm of voltage presence and yet they have not locked out the instrument operation when the voltage is present. I would have thought that was a programming issue and could easily be rectified.


Whilst the instrument records a one minute insulation resistance value, there is no built in timer and no DAR or PI ratio values displayed, that is common place on high end insulation testers these days. The maximum insulation reading limits are just too low for modern day insulation systems. I like to see the insulation limits go up to 40 to 50 GOhms on all ranges, to be able to accommodate DAR and PI ratio tests.


The bluetooth connection is really not that useful. I would have expected that they could have at least added logging functionality to allow the ratio tests to be carried out, but to only be able to store a single value, it is quicker and simpler to just write it down. Again this functionality falls quite behind something like the Fluke Connect range. However, unlike expanding the insulation reading capability, I would have thought that adding the logging function to the software would be easy to do to improve on the functionality of the IR4058.