Choosing Testing and Tagging Equipment
When looking for test and tag equipment, you will notice the large range you have to choose from, with all manufacturers claiming to meet Australian and New Zealand Standards. But this is not true.
The tests that are required to meet AS/NZ 3760: 2003 are as follows
The AS/NZ 3760 states that the earth resistance of the appliance can be tested either:
1. With a current between 100-200mA this is called a earth continuity
2. With a current of 10A this is called a routine test or,
3. With a current of 25A this is called a earth bond test
Each of these three tests has their advantages
A low current test is ideals for pieces of equipment with functional or signal earths. This is a circuit that has the earth that is connected through the circuit board. These pieces of equipment are not very common but can be found on scientific equipment and high end audio equipment (can be found at film, TV and sound studios). The users of this equipment normal know that it is earthed this way.
A disadvantage of an earth continuity test is that it will still pass with only one strand of wire connected in the earth. This is not sufficient for carrying large fault current. And if someone was to touch external metal during such fault the person is likely to be electrocuted.
There is little advantage to a routine test. But often testers that only use this test will be smaller and lighter that a 25A test due to the small transformer.
Earth Bond Test
High current tests are good to make sure that there is a good connection in the earthing conductor. If there is any less that five strands connected in the earth the test will fail. The disadvantage is with high current tests if the conductor is lightly corroded the appliance will still pass
For simplicity we can place the test and tag equipment in one of three distinct categories. The following is a guide to the different types, and highlights features to look for.
Simple PASS/FAIL types
PASS/FAIL type testers give a simple pass or fail test result allowing no interpretation of the test data. Some of the tester on the market will only carry out insulation and earth continuity tests or has an additional accessory to perform a leakage test and as a result will not be able to test appliances with Surge protectors (this is because AS/NZ 3760 states that a insulation resistance test or earth leakage test must be performed. Appliances with surge protectors will fail an insulation resistance test as a result the only way to test these appliances is to perform a leaking test). If the tester can not carry out the leakage test than only appliances with no electronic switching can be tested.
PASS/FAIL testers have the advantage of being easy to use but can have a limited practical use.
Manual Recording PAT Testers
Manual PAT testers give much more functionality than the simple PASS/FAIL testers. As well as the PASS/FAIL these tester will all so give numeric results. These testers have standard Insulation and Earth Continuity tests, and most also carry out an Earth Leakage.
Downloadable PAT Testers
For testing large amounts of equipment a testers that automates the process and has recording capabilities is more suitable. These testers are able to initiate a pre-programmed test sequence via a shortcut menu. Test data, including the overall PASS or FAIL result, is stored for downloading and most of can be connected to a test and tag printer to print test labels. These testers often have a bewildering amount of features.