Quick Answer: How Do You Calculate Insulation Resistance?

What is a good Megger reading?

Anything reading between 2 megohms and 1000 megohms is usually considered a good reading, unless other problems have been noted.

Anything less than 2 megohms indicates an insulation problem..

What is the test voltage for insulation resistance?

500 VFor most circuits with a nominal operating voltage of 500 V or less, the insulation test voltage should be 500 V. Before testing is carried out, the loads must be disconnected along with surge protection devices and any electronic equipment that might be damaged by the test.

How do you read Megger results?

If the megger reads a resistance under 1 (1,000 ohms) on your meter after the initial 60-second interval, the cable has failed and the cable should be removed. If the megger reads a resistance between 1-1.25 on your meter, then the cable passes. Any reading above 1.25 is considered excellent.

Is a Megger AC or DC?

Megger is an instrument used for measuring insulation resistance of a cable, but the cable that is to be tested is used in AC lines and the megger uses DC as the testing voltage.

What is the lowest acceptable insulation resistance for a cable?

1 MΩPerform the insulation resistance test between conductors at a reduced test voltage of 250 V DC. However, where this option is used, the minimum acceptable insulation resistance remains 1 MΩ.

How is IR value calculated?

The Insulated Power Cable Engineers Association (IPCEA) provides the formula to determine minimum insulation resistance values. R = IR Value in MΩs per 1000 feet (305 meters) of cable….HV test on new XLPE cable (As per ETSA Standard)ApplicationTest VoltageMin IR ValueAfter repairs – Insulation5KV DC1000MΩ3 more rows•Apr 29, 2012

How do you calculate minimum insulation resistance?

The rule may be stated: Insulation resistance should be approximately one megohm for each 1,000 volts of operating voltage, with a minimum value of one megohm. For example, a motor rated at 2,400 volts should have a minimum insulation resistance of 2.4 megohms.

What is meant by insulation resistance?

An insulation resistance (IR) test measures the total resistance between any two points separated by electrical insulation. The test, therefore, determines how effective the dielectric (insulation) is in resisting the flow of electrical current.

What is insulation resistance meter?

Portable insulation resistance testers and megohmmeters are designed to help prevent hazards such as electric shock and short-circuits caused when the insulation in electrical devices, parts, and equipment used in industrial plants, buildings, and other settings degrades over long periods of use.

How many ohms should a motor read?

0.5 ohmsEarth Continuity and Resistance Test A good motor should read less than 0.5 ohms. Any value greater 0.5 ohms indicate trouble with the motor.

Why Megger test is done?

The Megger test is a method of testing making use of an insulation tester resistance meter that will help to verify the condition of electrical insulation. Insulation resistance quality of an electrical system degrades with time, environment condition i.e. temperature, humidity, moisture and dust particles.

What is a bad insulation resistance reading?

The purpose of the IR test is to check for damaged insulation, this can be mechanical damage or damage by heat, (overloaded cables), readings less than 2 Mohm indicate damaged insulation, readings of 2-50 Mohm are indicative of long circuit lengths, moisture and contamination and do not indicate the insulation quality, …

What is the instrument used to measure insulation resistance?

megohmmeterA megohmmeter (also called insulation resistance tester, teraohmmeter) is then used to measure the ohmic value of an insulator under a direct voltage of great stability.

Whats is an insulator?

: one that insulates: such as. a : a material that is a poor conductor (as of electricity or heat) — compare semiconductor. b : a device made of an electrical insulating material and used for separating or supporting conductors.

What are the factors that affect the insulation resistance?

The factors that commonly affect the insulation resistance are:Surface condition. For example oil or carbon dust on the equipment’s surface that can lower the insulation resistance.Moisture. … Temperature.Feb 11, 2015

How do you read a Megger?

Select 500 volts DC or 1000 volts DC as the test voltage on your Megger, depending on the model you are using. Check whether your model has an integrated voltage tester for live circuits. If it doesn’t, check the circuits to be tested with a voltage tester to make sure they are not live.