How does a megger tester work?

Megger MIT515 (1001-936) 5kV Megohmmeter-
Megger insulation resistance.

How does a megger tester work? In order for you to understand how a megger tester works, you must know what a megger is. A megger is an electrical instrument that measures insulation resistance.

An insulation resistance test is performed in order to ensure that the insulation of conductors, accessories and equipment is in a healthy condition.

Knowing the state of the insulation resistance in conductors will prevent dangerous leakage current between conductors and between conductor and earth. This test will indicate whether a short circuit exists.

Table of contents

What is a megger test.

As stated earlier, a megger test is a test that is conducted on conductors, accessories and equipment to determine the state of the insulation material.

In short, a megger test is an insulation resistance test.

How does a megger tester work?

A Megger tester works on the principle of electromagnetic attraction. When a primary coil that is carrying current is placed near a magnetic field it experiences a force.

This force produces a torque that deflects the pointer of the device which gives the reading.

Megger tester definition anatomy.

megger tester definition anatomy
Credit circuit globe.

Why is a megger test done?

In any electrical installation, the installation loses its usefulness as time passes by, meaning that the quality of the insulating materials in conductors and equipment deteriorates with the growing age of the installation.

What makes the insulating materia deteriorate.

There are a lot of things that can make the insulation material become less effective. Among them is

  • Environmental conditions
  • Temperature
  • Humidity
  • Moisture
  • Dust particles
  • Electrical and mechanical stress.

When do you conduct a megger test? At times, you will conduct a megger test when it is required by your insurance company. Or when your house was on fire, and you want to know the integrity of the installation after the fire.

How to do a megger test.

The following procedure is used during the measuring of insulation resistance test.

  • Disconnet all iterm of equipment such as capacitors and indicator lamps,as these are likely to give misleading results.
  • Remove any iterms of equipment likely to be damaged by the test such as dimmer switches and electronics timers.
  • Remove all lamps and accessories and disconnect fluorescents and discharge fittings.
  • Ensure that the installation is disconnected from the supply,all fuses are in place circuit breakers and are in the on position.
  • Join togther all line conductors of the supply and test between the join and earth.Alternatively,test between each line conductor and earth in turn.
  • Test between the line and neutral,for three phase system,join together all lines and test between this join and neutral.Then test between each of the lines.Alternatively,test between each of the line conductors in tern.
  • Installation incorperating two way lightimg system should be tested twice with the two way switches in alternate position.

Megger reading charts.

Any reading above 1mohm is good reading.

Test voltage.Application.
5O-250VTelecoms and Datacom
500VBuilding wiring installations and maintenance
600V600V Equipments
1000VTroubleshooting, lower limit, medium voltage equipment

Test voltage vs Equipment rating.

Equipment in AC Rating.DC test voltage.
100V100-250V
440-550V500 and 1000V
2400 V1000-2500V
4160V1000V-5000V

How to interpret megger reading.

ConditionWhat to do
Fair to high values and well maintained.No cause for concern
Fair to high values but showing a constant tendency towards lower valuesLocate and remedy the cause and check the downwards trend.
Low but well maintainedCondition is probably alright but the cause of the low value should be checked.
So low as to be unsafeClean, Dry out, or otherwise raise the values before placing equipment in service. (Test wet equipment while drying out.)
Fair or high values previously well maintained but showing sudden loweringMake test at frequent intervals until the cause of low values is located and remedied. Or until the values have become steady at a lower level but safe for operation: Or until values become so low that it is unsafe to keep the equipment in operation.

For many years, maintenance professionals have used the one mega ohms rule to establish the allowable lower limits for insulation resistance.

Insulation resistance should be approximately one megaohm for every 1000 volts of an operating volt, with a minimum value of one megaohm.

In practice, megaohms reading values for new installations and equipment is considerably above the acceptable minimum value when in good condition.

Therefore it’s a good practice to check the insulation of an installation or equipment at regular intervals. This practice will enable you to know how the insulation is doing over a certain period.

By taking readings periodically, and reading them, you have a better basis for judging the actual insulation condition.

Any persistent downwards trend is usually a fair warning of trouble ahead.

megger 1kv insulation tester price.

There are a lot of brands that make insulation resistance testers. Renowned manufacturer of insulation resistance tester among others includes fluke and megger. Here I am going to conceder fluke and megger prices for a 1000V Megger insulation tester price.

The first megger 1KV insulation tester price is for Megger MIT430/2 CAT IV Insulation tester. This tester is priced at $1085.00 USD. You can buy it here.

Megger MIT430/2 CAT IV Insulation tester. Description and Sepecifications.

Megger MIT430/2 CAT IV Insulation tester-
Megger insulation tester.

Descriptions features and benefits.

  • Designed for Electrical and Industrial testing
  • Insulation testing up to 1000 V and 200 GΩ range
  • Stabilised insulation test voltage
  • Single range, faster continuity testing from 0.01 Ω to 1 MΩ
  • Adjustable insulation test voltage from 10 V to 1000 V
  • 600 V Trms AC and DC voltage measurement
  • Test result storage and Bluetooth® downloading
  • Live circuit detection and protection
  • Rechargeable options for mains and car charging
  • CAT IV 600 V and IP54

What is the meaning of CAT IV 600V?

The CAT IV ratings define the overvoltage installation categories that apply to low voltage systems of <1000 Volts test equipment as defined in IEC 1010 and UL61010-1 standards. This describes an electrical components ability to withstand impulse/transient voltage. The rating of our voltage indicators allows their use as permanently mounted test equipment used in fixed installations such as switchgear, MCCBs, bus and feeders in industrial plants and low voltage connections made to utility power.

CAT III is for distribution wiring, including main busses, feeders, and branch circuits with permanently installed loads. The highest is CAT IV, which is an installation at the origin or at the utility level. 

IP54. Protected from limited dust ingress. Protected from water spray from any direction.

Applications

  • Electrical installations
  • Cable testing
  • Motor testing
  • Automotive
  • ESD
  • Panel building
  • Avionics
  • Maintenance

You can get the user manual for the Megger MIT430/2 CAT IV Insulation tester here.

Megger MIT430/2 Specifications

Test voltage50 V, 100 V, 250 V, 500 V, 1000 V
Display rangeAnalogue: 1 GΩ full scale
Resolution0.1 kΩ
Short circuit/charge current2 mA +0% -50% to EN 61557-2 (2007)
Open circuit voltage insulation-0% +2% ± 2V
Test current1 mA at min. pass value of insulation to a maximum of 2 mA max.
Leakage10% ±3 digits
Voltage3% ±3 digits ±0.5% of rated voltage
Timer control60-second countdown timer
Continuity measurement0.01 Ω to 999 kΩ (0 to 1000 kΩ on the analogue scale)
Open circuit voltage5 V ± 1 V
Test current200 mA (–0 mA +20 mA), (0.01 Ω to 4 Ω)
PolaritySingle polarity (Default) / Dual polarity (configurable on setup).
Lead resistanceNull up to 9.00 Ω
Voltage rangeAC: 10 mV to 600 V TRMS sinusoidal (15 Hz to 400 Hz) DC: 0 to 600 V
Frequency measurement range15 Hz – 400 Hz
Frequency measurement accuracy±0.5% ± 1digit (100 Hz to 400 Hz unspecified)
Storage capacity>1000 test results
Data downloadBluetooth® wireless, Bluetooth® Class II
Power supply6 x 1.5 V cells type IEC LR6 (AA, MN1500, HP7, AM3 R6HP) Alkaline 6 x 1.2 V NiMH rechargeable cells may be used
Battery life3000 insulation tests with a duty cycle of 5 sec ON /55 sec OFF @ 1000 V into 1 MΩ
megger MIT 430/2 Specifications

Click here for complete specifications on the Megger MIT430/2

How does a megger tester work?

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