Portable Appliance Testers - Equipment Specifications & Features
When you start looking for a portable appliance tester, the first thing you will notice is the large range you have to choose from. The following is a guide to the different types, and highlights features to look for.
Earth Continuity - Soft Test
All modern PAT testers are able to perform a low current earth continuity test, this is usually referred to as a 'soft test'. The test current can be within the range of 20mA to 200mA, but 100mA or 200mA is typical. Somewhat confusingly, equipment manufacturers use differing terminology for this test. It may also be referred to as 'Earth Screen Test', 'Screen Bond Test' or 'Continuity Test'. This test is used for IT equipment where the primary purpose of the earth connection is for screening purposes and a high current earth continuity test may damage the equipment. The 3rd Edition of the IEE Code of Practice states that this test can be carried out on all class 1 equipment, not just IT equipment. This has led to a range of mainly battery operated testers being introduced that do not carry out a high current earth continuity test. Some older testers may not have a soft test function and therefore are not suitable for testing IT equipment.
Earth Continuity - Hard Test
The high current earth continuity test (hard test) is carried out at a current of not less than 1.5 times the rating current of the appliance, and no greater than 25 amps. The purpose of this high current test is to ensure any potentially corroded earth wires are suitably stressed, especially so on appliances that are susceptible to corrosion such as fridges, washing machines, kettles, dryers etc. Some battery powered testers do not have a high current earth continuity test.
Insulation Test (500V & 250V)
The insulation resistance test is normally measured by applying a test voltage of 500 Vdc. For some sensitive electronic equipment and equipment incorporating surge protection devices, the 500V test may not always be suitable. In such circumstances a reduced voltage, usually 250V, is used. Alternatively the insulation test may be replaced with an earth leakage test or touch current test.
Earth Leakage Test (230V & 110V)
The earth leakage test, also known as the protective conductor current test, is an additional or complementary test to the insulation test. This test is used where the insulation test gives suspect results or can not be used. A typical application is for testing equipment containing a heating element, such as a kettle, where the properties of the element may give a misleading insulation reading. Some testers can only carry out this test on 230V, others can also test 110V equipment.
Substitute Earth Leakage Test
The substitute leakage test is similar to the leakage test but is carried out at a lower voltage. This is useful for testing equipment that you do not want to power up for short periods of time, i.e. a computer. However this test does have limitations because appliances with electronic switches, relays or other active circuitry, will not be tested beyond the switch.
The touch current test is used as an alternative to the earth leakage test for class 2 equipment.
Load Test (230V & 110V)
The load test is usually performed at the same time as the earth leakage test to measure the power and/or the current the appliance is consuming. An abnormal power consumption may indicate potential faults with an appliance. As with the earth leakage test, some testers can only carry out this test on 230V, others can also test 110V equipment.
The flash test, also known as dielectric strength testing or hi-pot testing, is not normally carried out as part of the standard in-service inspection and testing and is usually only carried out by the appliance manufacturer.
The IEE Code of Practice recommends that in addition to the basic functional test, the trip time of portable RCDs should be tested. Some PAT testers now incorporate this function.
Tester Types & Features
Simple PASS/FAIL types
PASS/FAIL or GO/NO GO, type testers give a simple pass or fail test result allowing no interpretation of the test data. These testers generally only carry out insulation and earth continuity tests. Most PASS/FAIL PAT testers do not have a selectable Earth Continuity test current.
PASS/FAIL testers have the advantage of being easy to use but have limited practical use.
Manual PAT Testers
Manual PAT testers give much more functionality and display a test readings not just a pass or fail result, however they do require a level of understanding to correctly interpret the test data. As well as the standard Insulation and Earth Continuity tests, many also carry out Earth Leakage and Load tests. Look for testers with selectable Earth continuity test currents enabling the testing of IT equipment.
Downloadable PAT Testers
For testing large amounts of equipment a tester that automates the process and has recording capabilities is more suitable. These testers are able to initiate a pre-programmed test sequence. Test data, including the overall PASS or FAIL result, is stored for downloading or printing out.
PAT Equipment manufacturers and suppliers include - Alphatek, Avo, Fluke, Kewtech, Martindale, Megger, Metrel, Seaward, Robin, Transmille