Insulation Resistance (IR) Values

Introduction:

The measurement of insulation resistance is a common routine test performed on all types of electrical wires and cables. As a production test, this test is often used as a customer acceptance test, with minimum insulation resistance per unit length often specified by the customer. The results obtained from IR Test are not intended to be useful in finding localized defects in the insulation as in a true HIPOT test, but rather give information on the quality of the bulk material used as the insulation.

Even when not required by the end customer, many wire and cable manufacturers use the insulation resistance test to track their insulation manufacturing processes, and spot developing problems before process variables drift outside of allowed limits.

 Selection of IR Testers (Megger):

  • Insulation testers with test voltage of 500, 1000, 2500 and 5000 V are available.
  • The recommended ratings of the insulation testers are given below:
Voltage Level IR Tester
650V 500V DC
1.1KV 1KV DC
3.3KV 2.5KV DC
66Kv and Above 5KV DC

 Test Voltage for Meggering:

  • When AC Voltage is used, The Rule of Thumb is Test Voltage (A.C) = (2X Name Plate Voltage) +1000.
  • When DC Voltage is used (Most used in All Megger), Test Voltage (D.C) = (2X Name Plate Voltage).
Equipment / Cable Rating DC Test Voltage
24V To 50V 50V To 100V
50V To 100V 100V To 250V
100V To 240V 250V To 500V
440V To 550V 500V To 1000V
2400V 1000V To 2500V
4100V 1000V To 5000V

 Measurement Range of Megger:

Test voltage Measurement Range
250V DC 0MΩ to 250GΩ
500V DC 0MΩ to 500GΩ
1KV DC 0MΩ to 1TΩ
2.5KV DC 0MΩ to 2.5TΩ
5KV DC 0MΩ to 5TΩ

 Precaution while Meggering:

Before Meggering:

  • Make sure that all connections in the test circuit are tight.
  • Test the megger before use, whether it gives INFINITY value when not connected, and ZERO when the two terminals are connected together and the handle is rotated.

During Meggering:

  • Make sure when testing for earth, that the far end of the conductor is not touching, otherwise the test will show faulty insulation when such is not actually the case.
  • Make sure that the earth used when testing for earth and open circuits is a good one otherwise the test will give wrong information
  • Spare conductors should not be meggered when other working conductors of the same cable are connected to the respective circuits.

After completion of cable Meggering:

  • Ensure that all conductors have been reconnected properly.
  • Test the functions of Points, Tracks & Signals connected through the cable for their correct response.
  • In case of signals, aspect should be verified personally.
  • In case of points, verify positions at site. Check whether any polarity of any feed taken through the cable has got earthed inadvertently.

Safety Requirements for Meggering:

  • All equipment under test MUST be disconnected and isolated.
  • Equipment should be discharged (shunted or shorted out) for at least as long as the test voltage was applied in order to be absolutely safe for the person conducting the test.
  • Never use Megger in an explosive atmosphere.
  • Make sure all switches are blocked out and cable ends marked properly for safety.
  • Cable ends to be isolated shall be disconnected from the supply and protected from contact to supply, or ground, or accidental contact.
  • Erection of safety barriers with warning signs, and an open communication channel between testing personnel.
  • Do not megger when humidity is more than 70 %.
  • Good Insulation: Megger reading increases first then remain constant.
  • Bad Insulation: Megger reading increases first and then decreases.
  • Expected IR value gets on Temp. 20 to 30 decree centigrade.
  • If above temperature reduces by 10 degree centigrade, IR values will increased by two times.
  • If above temperature increased by 70 degree centigrade IR values decreases by 700 times.

How to use Megger:

  • Meggers is equipped with three connection Line Terminal (L), Earth Terminal (E) and Guard Terminal (G).

  • Resistance is measured between the Line and Earth terminals, where current will travel through coil 1. The “Guard” terminal is provided for special testing situations where one resistance must be isolated from another. Let’s us check one situation where the insulation resistance is to be tested in a two-wire cable.
  • To measure insulation resistance from a conductor to the outside of the cable, we need to connect the “Line” lead of the megger to one of the conductors and connect the “Earth” lead of the megger to a wire wrapped around the sheath of the cable.

  • In this configuration the Megger should read the resistance between one conductor and the outside sheath.
  • We want to measure Resistance between Conductor- 2To Sheaths but Actually Megger measure resistance in parallel with the series combination of conductor-to-conductor resistance (Rc1-c2) and the first conductor to the sheath (Rc1-s).
  • If we don’t care about this fact, we can proceed with the test as configured. If we desire to measure only the resistance between the second conductor and the sheath (Rc2-s), then we need to use the megger’s “Guard” terminal.

  • Connecting the “Guard” terminal to the first conductor places the two conductors at almost equal potential. With little or no voltage between them, the insulation resistance is nearly infinite, and thus there will be no current between the two conductors. Consequently, the Megger’s resistance indication will be based exclusively on the current through the second conductor’s insulation, through the cable sheath, and to the wire wrapped around, not the current leaking through the first conductor’s insulation.
  • The guard terminal (if fitted) acts as a shunt to remove the connected element from the measurement. In other words, it allows you to be selective in evaluating certain specific components in a large piece of electrical equipment. For example consider a two core cable with a sheath. As the diagram below shows there are three resistances to be considered.

  • If we measure between core B and sheath without a connection to the guard terminal some current will pass from B to A and from A to the sheath. Our measurement would be low. By connecting the guard terminal to A the two cable cores will be at very nearly the same potential and thus the shunting effect is eliminated.

(1) IR Values For Electrical Apparatus & Systems:

(PEARL Standard / NETA MTS-1997 Table 10.1)

Max.Voltage Rating Of Equipment Megger Size

Min.IR Value

 

250 Volts

500 Volts

25 MΩ

600 Volts

1,000 Volts

100 MΩ

5 KV

2,500 Volts

1,000 MΩ

8 KV

2,500 Volts

2,000 MΩ

15 KV

2,500 Volts

5,000 MΩ

25 KV

5,000 Volts

20,000 MΩ

35 KV

15,000 Volts

100,000 MΩ

46 KV

15,000 Volts

100,000 MΩ

69 KV

15,000 Volts

100,000 MΩ

One Meg ohm Rule for IR Value for Equipment:

  • Based upon equipment rating:
  • < 1K V = 1 MΩ minimum
  • >1KV = 1 MΩ /1KV

As per IE Rules-1956:

  • At a pressure of 1000 V applied between each live conductor and earth for a period of one minute the insulation resistance of HV installations shall be at least 1 Mega ohm or as specified by the Bureau of Indian Standards.
  • Medium and Low Voltage Installations- At a pressure of 500 V applied between each live conductor and earth for a period of one minute, the insulation resistance of medium and low voltage installations shall be at least 1 Mega ohm or as specified by the Bureau of Indian Standards] from time to time.

As per CBIP specifications the acceptable values are 2 Mega ohms per KV

(2) IR Value for Transformer:

  • Insulation resistance tests are made to determine insulation resistance from individual windings to ground or between individual windings. Insulation resistance tests are commonly measured directly in megohms or may be calculated from measurements of applied voltage and leakage current.
  • The recommended practice in measuring insulation resistance is to always ground the tank (and the core). Short circuit each winding of the transformer at the bushing terminals. Resistance measurements are then made between each winding and all other windings grounded.

  • Windings are never left floating for insulation resistance measurements. Solidly grounded winding must have the ground removed in order to measure the insulation resistance of the winding grounded. If the ground cannot be removed, as in the case of some windings with solidly grounded neutrals, the insulation resistance of the winding cannot be measured. Treat it as part of the grounded section of the circuit.
  • We need to test winding to winding and winding to ground ( E ).For three phase transformers, We need to test winding ( L1,L2,L3 ) with substitute Earthing for Delta transformer or winding ( L1,L2,L3 ) with earthing ( E ) and neutral ( N ) for wye transformers.

IR Value for Transformer

(Ref: A Guide to Transformer Maintenance by. JJ. Kelly. S.D Myer)

Transformer Formula
1 Phase Transformer IR Value (MΩ) = C X E / (√KVA)
3 Phase Transformer (Star) IR Value (MΩ) = C X E (P-n) / (√KVA)
3 Phase Transformer (Delta) IR Value (MΩ) = C X E (P-P) / (√KVA)
Where C= 1.5 for Oil filled T/C with Oil Tank, 30 for Oil filled T/C without Oil Tank or Dry Type T/C.
  •  Temperature correction Factor (Base 20°C):
Temperature correction Factor

OC

OF

Correction Factor

0

32

0.25

5

41

0.36

10

50

0.50

15

59

0.720

20

68

1.00

30

86

1.98

40

104

3.95

50

122

7.85

  • Example: For 1600KVA, 20KV/400V,Three Phase Transformer
  • IR Value at HV Side= (1.5 x 20000) / √ 1600 =16000 / 40 = 750 MΩ at 200C
  • IR Value at LV Side = (1.5 x 400 ) / √ 1600= 320 / 40 = 15 MΩ at 200C
  • IR Value at 300C =15X1.98= 29.7 MΩ

Insulation Resistance of Transformer Coil

Transformer

Coil  Voltage

Megger Size

 

Min.IR Value Liquid Filled T/C

 

Min.IR Value Dry Type T/C

0 – 600 V

1KV

100 MΩ

500 MΩ

600 V To 5KV

2.5KV

1,000 MΩ

5,000 MΩ

5KV To 15KV

5KV

5,000 MΩ

25,000 MΩ

15KV To 69KV

5KV

10,000 MΩ

50,000 MΩ

 IR Value of Transformers:

Voltage Test Voltage (DC)  LV side Test  Voltage (DC) HV side Min IR Value
415V 500V 2.5KV 100MΩ
Up to 6.6KV 500V 2.5KV 200MΩ
6.6KV to 11KV 500V 2.5KV 400MΩ
11KV to 33KV 1000V 5KV 500MΩ
33KV to 66KV 1000V 5KV 600MΩ
66KV to 132KV 1000V 5KV 600MΩ
132KV to 220KV 1000V 5KV 650MΩ

 Steps for measuring the IR of Transformer:

  • Shut down the transformer and disconnect the jumpers and lightning arrestors.
  • Discharge the winding capacitance.
  • Thoroughly clean all bushings
  • Short circuit the windings.
  • Guard the terminals to eliminate surface leakage over terminal bushings.
  • Record the temperature.
  • Connect the test leads (avoid joints).
  • Apply the test voltage and note the reading. The IR. Value at 60 seconds after application of the test voltage is referred to as the Insulation Resistance of the transformer at the test temperature.
  • The transformer Neutral bushing is to be disconnected from earth during the test.
  • All LV surge diverter earth connections are to be disconnected during the test.
  • Due to the inductive characteristics of transformers, the insulation resistance reading shall not be taken until the test current stabilizes.
  • Avoid meggering when the transformer is under vacuum.

Test Connections of Transformer for IR Test (Not Less than 200 MΩ):

  • Two winding transformer:
  1. (HV + LV) – GND
  2. HV – (LV + GND)
  3. LV – (HV + GND)
  • Three winding transformer:
  1. HV – (LV + TV + GND)
  2. LV – (HV + TV + GND)
  3. (HV + LV + TV) – GND
  4. TV – (HV + LV + GND)
  • Auto transformer (two winding):
  1. (HV + LV) – GND
  • Auto Transformer (three winding):
  1. (HV + LV) – (TV + GND)
  2. (HV + LV + TV) – GND
  3. TV – (HV + LV + GND)

For any installation, the insulation resistance measured shall not be less than:

  • HV – Earth 200 M Ω
  • LV – Earth 100 M Ω
  • HV – LV 200 M Ω

 Factors affecting on IR value of Transformer

The IR value of transformers are influenced by

  • surface condition of the terminal bushing
  • quality of oil
  • quality of winding insulation
  • temperature of oil
  • duration of application and value of test voltage

(3) IR Value for Tap Changer:

  • IR between HV and LV as well as windings to earth.
  •  Minimum IR value for Tap changer is 1000 ohm per volt service voltage

 (4) IR Value for Electric motor:

For electric motor, we used a insulation tester to measure the resistance of motor winding with earthing ( E ).

  • For rated voltage below 1KV, measured with a 500VDC Megger.
  • For rated voltage above 1KV, measured with a 1000VDC Megger.
  • In accordance with IEEE 43, clause 9.3, the following formula should be applied.
  • Min IR Value (For Rotating Machine) =(Rated voltage (v) /1000) + 1

As per IEEE 43 Standard 1974,2000

IR Value in MΩ
IR (Min) = kV+1 For most windings made before about 1970, all field windings, and others not described below
IR (Min) = 100 MΩ For most dc armature and ac windings built after about 1970 (form wound coils)
IR (Min) = 5 MΩ For most machines with random -wound stator coils and form-wound coils rated below 1kV
  • Example-1: For 11KV, Three Phase Motor.
  • IR Value =11+1=12 MΩ but as per IEEE43 It should be 100 MΩ
  • Example-2: For 415V,Three Phase Motor
  • IR Value =0.415+1=1.41 MΩ but as per IEEE43 It should be 5 MΩ.
  • As per IS 732 Min IR Value of Motor=(20XVoltage(p-p/(1000+2XKW))

IR Value of Motor as per NETA ATS 2007. Section 7.15.1

Motor Name Plate (V) Test Voltage Min IR Value
250V 500V DC 25 MΩ
600V 1000V DC 100MΩ
1000V 1000V DC 100MΩ
2500V 1000V DC 500MΩ
5000V 2500V DC 1000MΩ
8000V 2500V DC 2000MΩ
15000V 2500V DC 5000MΩ
25000V 5000V DC 20000MΩ
34500V 15000V DC 100000MΩ

IR Value of Submersible Motor:

IR Value of Submersible Motor

Motor Out off Well (Without Cable) IR Value
New Motor 20 MΩ
A used motor which can be reinstalled 10 MΩ
Motor  Installed in Well (With Cable)  
New Motor 2 MΩ
A used motor which can be reinstalled 0.5 MΩ

 (5) IR Value for Electrical cable and wiring:

  • For insulation testing, we need to disconnect from panel or equipment and keep them isolated from power supply. The wiring and cables need to test for each other ( phase to phase ) with a ground ( E ) cable. The Insulated Power Cable Engineers Association (IPCEA) provides the formula to determine minimum insulation resistance values.
  • R = K x Log 10 (D/d)

  • R =IR Value in MΩs per 1000 feet (305 meters) of cable.
  • K =Insulation material constant.( Varnished Cambric=2460, Thermoplastic Polyethlene=50000,Composite Polyethylene=30000)
    D =Outside diameter of conductor insulation for single conductor wire and cable
  • ( D = d + 2c + 2b diameter of single conductor cable )
    d – Diameter of conductor
    c – Thickness of conductor insulation
    b – Thickness of jacket insulation

HV test on new XLPE cable (As per ETSA Standard)

Application Test Voltage Min IR Value
New cables – Sheath 1KV DC 100 MΩ
New cables – Insulation 10KV DC 1000 MΩ
After repairs – Sheath 1KV DC 10 MΩ
After repairs – Insulation 5KV DC 1000MΩ

11kV and 33kV Cables between Cores and Earth (As per ETSA Standard)

Application Test Voltage Min IR Value
11KV New cables – Sheath 5KV DC 1000 MΩ
11KV After repairs – Sheath 5KV DC 100 MΩ
33KV no TF’s connected 5KV DC 1000 MΩ
33KV with TF’s connected. 5KV DC 15MΩ

IR Value Measurement (Conductors to conductor (Cross Insulation))

  • The first conductor for which cross insulation is being measured shall be connected to Line terminal of the megger. The remaining conductors looped together (with the help of crocodile clips) i. e. Conductor 2 and onwards, are connected to Earth terminal of megger. Conductors at the other end are left free.
  • Now rotate the handle of megger or press push button of megger. The reading of meter will show the cross Insulation between conductor 1 and rest of the conductors. Insulation reading shall be recorded.
  • Now connect next conductor to Line terminal of the megger & connect the remaining conductors to earth terminal of the megger and take measurements.

IR Value Measurement (Conductor to Earth Insulation)

  • Connect conductor under test to the Line terminal of the megger.
  • Connect earth terminal of the megger to the earth.
  • Rotate the handle of megger or press push button of megger. The reading of meter will show the insulation resistance of the conductors. Insulation reading shall be recorded after applying the test voltage for about a minute till a steady reading is obtained.

 IR Value Measurements:

  • If during periodical testing, insulation resistance of cable is found between 5 and 1 /km at buried temperature, the subject cable should be programmed for replacement.
  • If insulation resistance of the cable is found between 1000 and 100 /km, at buried temperature, the subject cable should be replaced urgently within a year.
  • If the insulation resistance of the cable is found less than 100 kilo ohm/km., the subject cable must be replaced immediately on emergency basis.

 (6) IR Value for Transmission / Distribution Line:

Equipment.                Megger Size Min IR Value
S/S .Equipments 5 KV 5000MΩ
EHVLines. 5 KV 10MΩ
H.T. Lines. 1 KV 5MΩ
LT / Service Lines. 0.5 KV 5MΩ

(7) IR Value for Panel Bus:

  • IR Value for Panel = 2 x KV rating of the panel.
  • Example, for a 5 KV panel, the minimum insulation is 2 x 5 = 10 MΩ.

 (8) IR Value for Substation Equipment:

Generally meggering Values of Substation Equipments are.

.Typical IR Value of S/S Equipments

Equipment   Megger Size IR Value(Min)

Circuit Breaker

(Phase-Earth)

5KV,10 KV

1000 MΩ

(Phase-Phase)

5KV,10 KV

1000 MΩ

Control Circuit

0.5KV

50 MΩ

CT/PT

(Pri-Earth)

5KV,10 KV

1000 MΩ

(Sec-Phase)

5KV,10 KV

50 MΩ

Control Circuit

0.5KV

50 MΩ

Isolator

(Phase-Earth)

5KV,10 KV

1000 MΩ

(Phase-Phase)

5KV,10 KV

1000 MΩ

Control Circuit

0.5KV

50 MΩ

L.A

(Phase-Earth)

5KV,10 KV

1000 MΩ

Electrical Motor

(Phase-Earth)

0.5KV

50 MΩ

LT Switchgear

(Phase-Earth)

0.5KV

100 MΩ

LT Transformer

(Phase-Earth)

0.5KV

100 MΩ

IR Value of S/S Equipments As per DEP Standard

Equipment

Meggering

IR Value at Commissioning Time (MΩ)

IR Value at Maintenance Time(MΩ)

Switchgear

HV Bus

200 MΩ

100 MΩ

LV Bus

20 MΩ

10 MΩ

LV wiring

5 MΩ

0.5 MΩ

Cable(min 100 Meter)

HV & LV

(10XKV) / KM

(KV) / KM

Motor & Generator

Phase-Earth

10(KV+1)

2(KV+1)

Transformer Oil immersed

HV & LV

75 MΩ

30 MΩ

Transformer Dry Type

HV

100 MΩ

25 MΩ

LV

10 MΩ

2 MΩ

Fixed Equipments/Tools

Phase-Earth

5KΩ / Volt

1KΩ / Volt

Movable Equipments

Phase-Earth

5 MΩ

1MΩ

Distribution Equipments

Phase-Earth

5 MΩ

1MΩ

Circuit Breaker

Main Circuit

2 MΩ / KV

 

Control Circuit

5MΩ

 

Relay

D.C Circuit-Earth

40MΩ

 

LT Circuit-Earth

50MΩ

 

LT-D.C Circuit

40MΩ

 

LT-LT

70MΩ

 

 (9) IR Value for Domestic /Industrial Wiring:

  • A low resistance between phase and neutral conductors, or from live conductors to earth, will result in a leakage current. This cause deterioration of the insulation, as well as involving a waste of energy which would increase the running costs of the installation.
  • The resistance between Phase-Phase-Neutral-Earth must never be less than 0.5 M Ohms for the usual supply voltages.
  • In addition to the leakage current due to insulation resistance, there is a further current leakage in the reactance of the insulation, because it acts as the dielectric of a capacitor. This current dissipates no energy and is not harmful, but we wish to measure the resistance of the insulation, so DC Voltage is used to prevent reactance from being included in the measurement.

 1 Phase Wiring:

  • The IR test between Phase-Natural to earth must be carried out on the complete installation with the main switch off, with phase and neutral connected together, with lamps and other equipment disconnected, but with fuses in, circuit breakers closed and all circuit switches closed.
  • Where two-way switching is wired, only one of the two stripper wires will be tested. To test the other, both two-way switches should be operated and the system retested. If desired, the installation can be tested as a whole, when a value of at least 0.5 M Ohms should be achieved.

3 Phase Wiring:

  • In the case of a very large installation where there are many earth paths in parallel, the reading would be expected to be lower. If this happens, the installation should be subdivided and retested, when each part must meet the minimum requirement.

  • The IR tests must be carried out between Phase-Phase-Neutral-Earth with a minimum acceptable value for each test of 0.5 M Ohms.

IR Testing for Low voltage

circuit voltage Test voltage IR Value(Min)
Extra Low Voltage 250V DC 0.25MΩ
Up to 500 V except for above 500 V DC 0.5MΩ
500 V To 1KV 1000 V DC 1.0MΩ
  •  Min IR Value = 50 MΩ / No of Electrical outlet. (All Electrical Points with  fitting & Plugs).
  • Min IR Value = 100 MΩ / No of Electrical outlet. (All Electrical Points without fitting & Plugs).

 Required Precautions:

  • Electronic equipment like electronic fluorescent starter switches, touch switches, dimmer switches, power controllers, delay timers could be damaged by the application of the high test voltage should be disconnected.
  • Capacitors and indicator or pilot lamps must be disconnected or an inaccurate test reading will result.
  • Where any equipment is disconnected for testing purposes, it must be subjected to its own insulation test, using a voltage which is not likely to result in damage. The result must conform with that specified in the British Standard concerned, or be at least 0.5 M Ohms if there is no Standard.
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About Jignesh.Parmar
Jignesh Parmar has completed his B.E(Electrical) from Gujarat University. He has more than 11 years experience in Power Transmission-Power Distribution-Electrical energy theft detection-Electrical Maintenance-Electrical Projects(Planning-Designing-coordination-Execution). He is Presently associate with one of the leading business group as a Assistant Manager at Ahmedabad,India. He is Freelancer Programmer of Advance Excel and design useful Excel Sheets of Electrical Engineering as per IS,NEC,IEC,IEEE codes. He is technical Author for "Electrical Mirror" and "Electrical India" Magazines. He is Technical Blogger and Familiar with English, Hindi, Gujarati, French languages. He wants to Share his experience & knowledge and help technical enthusiasts to find suitable solutions and updating themselves on various Engineering Topics.

86 Responses to Insulation Resistance (IR) Values

  1. modupalli says:

    Outstanding Stuff…. Thanks For Sharing..

  2. vilas K. says:

    Dear Sir Hats Off !! & many thanx for your invaluable contribution in enriching the experience of Elect. Engineers & making them available the fabulous data at a glance.. Pl keep posted. If U can throw some light on selection of MCB/MCCB & contactors in relation to their diff characteristics.

  3. varghese says:

    dear sir… is a great work…. thanks

    could u pls explain the effects of rise in temperature on insulation resistance of transformer.

  4. Barun Majumder says:

    Dear sir many many thanks for sharing valuable article of electrical engineering . I want to know more about electrical design (Distribution, industrial & commercial ) and protection system from your end point to point . If you have any book/site for those design please let me know the name.
    I am working as a design engineer but i am not enough confident about my design and protection system. i want your valuable assistance in this field .

    Thanking you
    Yours faithfully
    Barun Majumder

    Kolkata

  5. kumereshan P S says:

    Sir,
    great work,i want to know the IS standards for IR value of Sub station equipment

    With regards

    Kumereshan

  6. Honestly i am not quite good on electric thing and this one is very good for me to study so well and learn a lot many thanks for this article.

  7. keyur says:

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    Thanks
    keyur

  8. MANOHAR says:

    Dear sir

    I need calculation formula of IR Values of an elect drives

  9. Madanmohan says:

    Wonderful explanation. Really very much useful document. Thnak you very much

  10. sathesh says:

    Very nice sir.. Thanku..

  11. rehan says:

    good information, thanks for your time.

  12. custom milagros says:

    2 thumbs up.

  13. Gurmeet Singh says:

    Very -2 Thanks sir

  14. preeti says:

    thanks, very good information

  15. osarenkhoe nosa glory says:

    this is absolutely nice. a well written document. thanks.

  16. Naveen says:

    Thank you Sir, much appreciated

  17. A. Hasasn says:

    Dear Sir;
    Really your this article is very very important for electrical related people.Your this contribution is excellant. A lot of thanks sir.
    Kind Regardrs

  18. K.M.Pandey says:

    Respected Sir.

    This article very important and useful for all those person who are related with Electrical field. Thanks a lot for sharing your knowledge with all people. Really you are nice and gentleman.
    With regards,
    K.M.Pandey,

  19. ahmed nawaz says:

    Ch.Ahmed Nawaz

    thanks sir for giving very usefull information.

  20. radhakishan pawar says:

    thanks sir i have no word to explain how much it is useful to student.
    thanks again……

  21. THAKOR SANJAY says:

    I AM A TESTING ENGINEER…….THIS INFO. IS VERY USEFUL FOR ME
    VERY VERY THANKS FOR THIS …

  22. Vilas G. says:

    Thanks . valuable note for electrical engineers.

  23. Steve Arreola says:

    Thank you much for taking the time to share this information

  24. Mr. Judy Diano says:

    Thank you so much,for sharing Sir, I learned a lot of your link GOD BLESS

  25. arshad says:

    thanks for beautiful notes

  26. Jet Paliangayan says:

    how to do IR test for single core pvc/xlpe/pvc cables

  27. jamestryre says:

    great info, thx

  28. Thiyaga says:

    Incredible work. Hats off for your awesome articles. pl keep posting more and more

  29. sambasivarao chagantipati says:

    Very useful information

  30. rohtash verma( Himachal pradesh) says:

    Thanks parmar ji very use full information regarding IR value of electric motors

  31. M.Zaman says:

    thanks for valuable information.

  32. FELIX Jr. says:

    Please, you must also include here the Polarization Index (PI) as well for it’s significance and explain why it is required with respect to the IR test being done on the electrical equipment and the electrical cables and installations, as an additional information for the new commissioning engineers and enthusiasts. Supressing other comments are not at all interesting and helpfull.

    • Yes You are right PI value is as important as IR Value specially HV Equipments.
      Here I gave only Overview of IR Testing and it’s value.
      To rise comment is totally depend upon the reader.
      In near future I will definitely cover the Topic of PI.

      • deepak parmar says:

        I want to know the acceptable leakage current values in the HV testing as per IEC standards.

        And thanks for the info provided above

  33. sateesh says:

    excellent explanation about IR test
    thanks a lot.

  34. vincent says:

    Good knowledge.thank you.

  35. Anderson says:

    Excelente trabajo, quiero saber cuales son las normas que rigen estas pruebas y si existe alguna estandarización de resultados. Gracias

  36. Thanks for such a great article. Very interesting and informative. Thanks Buddy

  37. Diganta ku. Ray says:

    Thank you so much sir,this help me a lot in my field.its very very useful for those are in electrical line.

  38. JAYESH PATEL says:

    how many Insulation Resistance of the Whole Installation permissible ?
    how many Insulation Resistance Between Conductors ?
    how many Insulation Resistance Between Each Conductor & Earth ?

  39. Hello very nice blog!! Man .. Excellent .. Amazing .. I will bookmark your web site and take the feeds additionally?

    I am glad to find numerous helpful info here in the put up, we want work out more strategies on this regard, thank you for sharing.

    . . . . .

  40. fayyaz says:

    thks good information can you mail me how to check insulation of dc 24 volt system.
    also i want to know how insulation monitor works.

  41. sonu kumar says:

    thanks for this valueable data.

  42. Excellent information. Really appreciate the knowledge you have shared with readers.
    Sir can you pls tell me what should be minimum value of IR for PVC make busboot used for 11 KV , 22 KV , 33 KV and 66 KV.

    Regards
    Debashish Bhattacharya

  43. Gerald says:

    Thanks for sharing…

  44. CPR vittal says:

    excellent article.
    the formula for insulation resistance of a cable per 1000 ft.
    how to calculate it per meter or per feet.
    pl explain

  45. what precautions i should take when CT is connected in HT board and i have do megger.?

  46. ibnu says:

    lightning cable for crane – there are 2 point earth terminal, each has individual ground cable, i meggar 1kV both cable, gives different reading 200Mohm & almost infinity for another one. why? can accept the value?

  47. ibnu says:

    can 11kv cable, meggar at 1kv only, during before & after hipot test? (hipot at 30.5kv)

  48. parveen kumar says:

    dear sir i want to know why used in transformer secondary side very thin wire

  49. FELIX Jr. says:

    Yes, you can use 1kV DC- MEGGER TESTER prior to HIPOT Testing if your electrical cable is rated 11kV and HIGHER and if it has 130 % rated insulation. After HIPOT test, if successful, you can megger it again with 1kV only at no more than 1 minute just to make sure no damage has occurred during and after HIPOT TEST.

    By FMSJr. / Abu Dhabi, UAE

  50. Nasurudheen Kamal Basha says:

    Useful stuff.. Thanks for sharing!!

  51. MOHAMMAD says:

    THANKS ALOT VERY GREATFUL INFO

  52. Pushkar Singh says:

    Thanks for sharing excellent information.
    Pushkar Singh ONGC

  53. A V N Phanindra says:

    thank u so much sir its very brief and simple to understand clearly.

  54. ASMA says:

    WHAT WOULD BE THE MEGGAR REULT OF A GOOD CONDITION 25 KVA TRANSFORMER?
    I WILL BE OBLIGED..KINDLY HELP ME.

    • FELIX Jr. says:

      GOOD DAY ! Your posted question about the MEGGER result for a good condition for 25kVA Transformer is very general as you did not specify the input and output voltages of this electrical equipment and if it is oil immersed or dry type. At anyrate, assuming it’s oil filled step-up transformer, outdoor pole mounted, for a good IR result for primary winding, normally it should not be less than 500Megaohm and the secondary winding’s IR reading should be not less than 300Megaohm with respect to earth and higher between windings. Again, these are assumptions only and the higher the voltage rating of the transformer the higher IR reading should result. Defective insulations will read low values of IR readings and contaminated oil insulation, for oil immersed type transformers. For dry type Transfomers, the good IR readings of the windings are also in that vicinity but lower than oil immersed type.

  55. J.R Bohra says:

    very very helpful
    Thanks
    J,R Bohra
    Unique Engineer Noida

  56. Diptiranjan Nayak says:

    Thank u sir,
    I am clear about IR value.

  57. raghav says:

    dear sir,
    i need more information about how to calculate ir values and what principle it requires to calculate ir values?

  58. Musa says:

    Anybody can answer my query?

    We have 25kV AC system for Overhead Line Equipment (OHE). This system is installed for Electrified Train system (Railway project).

    We have conduct IR testing before charging the lines for each electrical subsection (the longest section about 20km). The result we achieved 0.5MOhm – 5MOhm (taken during night time) and 200MOhm – 700MOhm (taken during night time). The temperature during night time is around 27 – 28 degree Celsius (in Malaysia).

    We injecting megger size 5kV and result achieved as above. As mentioned in the article (i think it is similar to our system – IR value for transmission/ distribution line) which is stated Min. IR values shall be 10MOhm.

    Is it the result we achieved okay, especially the result taken during night time?

  59. sampath says:

    thank for more information now i harry to check insulation resistance long 132Kv transmission line & will have called you after testing

  60. SYAM says:

    Dear Jignesh,

    Just for curiosity can you please tell me what is the full form of “DEP” standards which you have mentioned under the section “IR Value of S/S Equipments As per DEP Standard”.

    Hope you will reply

    Regards

    SYAM

  61. Sekar Ram says:

    Mr Jignesh
    This is one of the greatest selfless efforts I have seen. This is pure social service. Hats off!!

  62. Stephen says:

    Hello. Question, if we have 5 conductors per phase on a lugs and we want to megger the groups, ie: phase to phase and phase to ground and the readings are above 1 M ohm, is that OK? We had previously meggered all the cabels individually prior to installing. The job was shut down for a while, and this is for a precaution, prior to re-energizing.

  63. vijay says:

    dear jignesh sir,

    Can i have the entire notes in site in form of book? How much does it cost?

  64. very very useful and very thanks for made me doubt clear..

  65. Michel says:

    thanks Bro that is too goooooooooooooood for us

  66. ESAKKIPANDI says:

    the explanation is excellent

  67. rahul jangme says:

    thank you sir

  68. ali says:

    thank you so much Dr

  69. Doma Hudu says:

    thank sir. I need a copy via my e-mail. please am wait for your response Sir.

  70. Srinivasan says:

    Thank you sir. Useful detail information.

  71. aby says:

    Sir,
    appreciate your ideas and procedures.
    May i know ,whether there is any necessity or mandatory rules saying that the speaker cables to be meggered?
    if yes,then what should be the applied voltage?

  72. roop says:

    dear mr Parmar first of all thanks for sharing the information

  73. roop says:

    we are building a 9 km road tunnel, we usually facing problem with ht cable, whenever it is damaged it took 3 to4 hour for jointing, lot of production loss please advise any alternate means of transmission of ht cable or any ht joint available around the world to do the jointing quickly.

  74. Felix Jr San Buenaventura says:

    THESE ARE GOOD INFORMATION AND REFERENCE FOR ALL ELECTRICAL ENGINEERS AND COMMISSIONING ENGINEERS BE IT IN DESIGN ENGINEERING OR IN COMMISSIONING WORKS OF PROJECTS RELATED TO ELECTRICAL POWER GENERATION, TRANSMISSION AND IN DISTRIBUTION SYSTEMS THE WORLD OVER. TIKE !, SALAMAT PO !, GRACIAS !, QZI QZI !, TERIMA KASIH !

  75. SB says:

    Thank you ever so much! For sharing such good info, extremely relevant.

  76. rd says:

    What is the minimum acceptable insulation resistance for 1.8 kv DC cables? temperature is around 50 deg C. My understanding is that IR decreases when there is increase in temperature. So how do i calculate Insulation resistance considering the temperature?

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