What causes low insulation resistance readings?

What causes low insulation resistance readings?

Low insulation resistance may be due to the age of the installation, or alternatively it may be caused by an individual circuit, which would merit further investigation. In summary, insulation resistance testing should be undertaken at relevant times during and on completion of an installation.

What is the difference between Megger and Hipot?

A megger is a megohmeter, measures insulation resistance. A hipot tester basically works the same way, but measures leakage current. If you see a fault with the megger, you will see a fault with the hipot. The hipot stresses the insulation weak points at higher voltage levels than the megger will.

What is the minimum acceptable insulation resistance?

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 does an insulation resistance test prove?

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 are the factors affecting 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.

How do I test my insulation with a Megger?

If you are testing insulation resistance to ground, place the positive probe on the ground wire or the grounded metal junction box and the negative probe on the conductor or terminal. Energize the Megger for 1 minute. Read the value of the resistance at the end of the minute test and note it in your table.

What is insulation resistance of motor?

Insulation Resistance (IR) is among the most common motor tests. In an IR or megohm test the voltage applied and the total leakage current are measured between the windings and the motor frame/ground. Ohms law is applied to calculate the resistance in megohms.

How do you test motor insulation resistance?

Perform an insulation resistance test on each conductor in the cable. Apply 1000 VDC for 1 min (one- minute insulation resistance test) to low voltage cables (1 kV or less) and use a megohmmeter, or insulation multimeter (IMM) to measure the insulation resistance.

How do you test a Megger on a 3 phase motor?

1. Turn off the power supply to the motor, usually accomplished by switching the circuit breaker.
2. Place one megger probe to the any mounting bolt on the breaker box to test for grounding continuity, then touch the other probe to a motor terminal.
3. Crank the handle for about a minute, and notice the resistance reading.

Can you test insulation resistance with a multimeter?

You use your insulation multimeter to check the insulation resistance of each conductor to ground and of each conductor to the other two. The insulation resistance readings are all over 1 gigohm, so it doesn’t seem to be an insulation problem.