The portable appliance testing (PAT) is the test carried out on Class I and II appliances. The purpose of this test is in order to ensure that there are adequate insulation between the parts of the user touchable metal parts and the appliances.
PAT testing a Class I appliance: For high insulation resistance you can plug the appliance in the Pat Tester. You have to make sure that the appliance is switched on. During the test, if there is more than 1 M ohm resistance between the the Live and the Neutral and the Earth pins, then there is adequate insulation and the appliance is considered safe.
PAT testing a Class II appliance: You can plug the appliance to a PAT Tester for high insulation resistance. You must be sure that the appliance is switched on. You can connect the test probe to the metallic part on the appliance. When the test is done, if there is more than 2 M ohm between the Live and the Neutral and any metallic part, then there will be adequate insulation and the appliance is considered safe. It's very important to connect the test probe to the metallic part on Class II appliance . This can require multiple tests . If it's not done, then any problem with the insulation will never be detected in the PAT testing.While carrying out this test there are number of practical things that must be taken into account.
Test voltage: This is carried out by using a voltage of 500 V. The surge protected appliances have components that present low resistance at the test voltage. While carrying the high insulation resistance test during the PAT testing, if you are failed on the surge protected appliances, it's very normal to repeat the test at lower 200V. If the PAT tester don't have a 200V test option, then it's adequate to make a note and pass the surge protected appliance. The PAT tester actually does the high insulation resistance test at the voltage of 300V and will pass the surge protected appliances.
Cooking and Heating appliances: In some of the appliances which uses the mineral insulated heating materials, the absorbed moisture can result in the failure during PAT testing. In this case, you have to switch on the appliance for a certain period in order to eject moisture and then retest.
Portable Appliance Test for Insulation Resistance