Pat teating is a process where electrical appliances are tested to ensure they are safe for use. It involves exposing the live and neutral conductors to a test voltage (usually 230V AC) and measuring their insulation resistance using a PAT tester or an ohmmeter. The equipment is then marked either ‘pass’ or ‘fail’ and a record of the results is kept. This allows the duty holder to identify any appliances that may require further investigation, repair or replacement.

There are different methods of pat testing, each suited to a particular type of appliance or test situation. The most common is the differential leakage current test. This method exposes the connecting live and neutral conductors to a high level of test voltage and measures the difference in current to determine whether or not there is any leakage current to earth. The other two tests are touch current and earth bonding or resistance. These involve connecting the test probe to any exposed metal parts of an item of equipment and sending a current through the protective earth pin in the mains plug. The tester then displays the resistance reading and, if an item is classed as a risk of shock, this indicates that there is insufficient contact between the live parts of the appliance and the earth.

Understanding PAT Testing: What You Need to Know

Extension lead testing is also possible with some testers that incorporate a specific IEC extension lead adapter. This enables the 13A plug on the extension lead to be connected to the IEC socket on the tester and the last socket on the end of the extension lead back into the IEC socket on the tester. This method requires great care to prevent any shock risk and is best carried out by a qualified professional.

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