what is a insulation test for?

Answer 1

an insulation test is designed to test the insulation of the czble meets the regulations which for a household it must be greater than 2Megaohms. If this is a new installation you must be cautious if it is below 999Megaohms because this is may show signs of leakge and damage. A test is preformed by sendind a voltage between two cable for instance live and neutral to find if there is any continuity between them. The test voltage is usually double the operating voltage.

Answer 2

There are actually two types of 'insulation tests'. One is to test between the insulation and ground; the other is to test for dielectric strength (insulation breakdown due to electrical stress).

To test for grounds, the instrument is called a MEGGAR. A direct current test voltage is applied to the conductor by the instrument, and the reading is taken between the conductor and ground. The test voltage needs to be applied and held for one minute. For most items, this test is done at 500 Vdc - some higher voltage applications (like high voltage motors and generators) use 1000 Vdc for the test. A 'pass' occurs when the reading is above a specified safe value - typically on the order of 200+ Megohms. (For residential applications, check your local building code ... it may have a much higher threshold value!). If you do not have the required minimum 'pass' value, the circuit fails the test and you'll need to investigate what's happened and (potentially) reinsulate.

To test for electrical stress, the test is called a HIPOT (short for high potential test). This occurs when the testing instrument generates a very high alternating current voltage and passes it through the wiring to be tested. Typically, this test is done on loads, not actual cabling. Most codes require that the investigation be conducted at a test voltage that is equal to twice the rated voltage of the equipment, plus 1000. The duration of the test is one minute ... if the insulation withstands the high voltage, the test is a success and the equipment 'passes'. Otherwise, you'll see some smoke and a small pinhole ... and the equipment has failed (requiring reinsulating and/or a complete rebuild).

Typically, a HIPOT test is a pass/fail criteria for electrical equipment. A MEGGAR test is more concerned with trending; it is used on a regular basis to 'predict' remaining insulation life. Note that the meggar test is ALSO temperature dependent! To ensure good trending, remember to always record the temperature at which the measurement was taken (and/or convert it to a standard value, like 40 C).

Answer 3

An electrical insulation test is carried out to confirm the insulation value of electrical cabling. The applied test voltage is usually twice the normal working voltage and the resultant insulation reading is in Mega Ohms. A value of Kilo Ohms would suggest insulation breakdown and unserviceability of the cabling.

Answer 4

in a domestic installation(house)in australia its to make sure there is no connection less than one million ohms between the conductors in the house and the earth (grounding )system...CHECK WITH YOUR LOCAL SUPPLY AUTHORITY..