?:| What do people think about portable (hand held batt) PAT testers and the low 200ma earth test current ? I have always thought that you put a large test current (25a) down the earth to find its a substancial fault circuit, cheers - Stuart.
PAT test earth current
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green-hornet
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It really does depend on what test you want to carry out.
Remember that type testing is very different than safety tests.
When a product is tested it must go through a vigorous safety check system which will push the product to destruction.
In normal everyday use it will never come under such abuse.
Common sense prevails that applied recognised testing procedures are carried out and that the findings are accurately recorded in a shedule of tests and a copy of such tests and findings are given to the client for safe keeping and reference.
For double insulated class 2 equipment I would doubt an earth fault would effect this equipment, simply because an earth is often absent from the circuit.
Remember that type testing is very different than safety tests.
When a product is tested it must go through a vigorous safety check system which will push the product to destruction.
In normal everyday use it will never come under such abuse.
Common sense prevails that applied recognised testing procedures are carried out and that the findings are accurately recorded in a shedule of tests and a copy of such tests and findings are given to the client for safe keeping and reference.
For double insulated class 2 equipment I would doubt an earth fault would effect this equipment, simply because an earth is often absent from the circuit.
Hi GH, Its not type testing its just regular PAT testing I am on about, perhaps I am the old school and think that you pass a large earth current down the cable looking for some resistance (which will show up) and not 200ma which will not test the circuit under fault conditions. cheers - Stuart.
bit like R1R2 on circuits. proves there is continuity at 200mA, but may go O/C at higher fault currents before the protection does
ericmark
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With IT equipment often the earth is connected through the printed circuit and 25A can damage the printed circuit which could lift and latter break. This is why we use the low current test. Where one knows there are no printed circuits then 25A is no problem.
Both high and low current testing have there merits.
High current testing can under certain circumstances detect damaged cables but the cable has to be severly damaged and the test duration has to be long enough to 'fuse' the remaining strands. I did some experiments on a 48 strand cable using a 25A test for 5s. With 42 strands cut i.e. only 6 remaining the cable could repeatedly carry 25A for 5s and so a high current earth test would not have detected the fault.
Low current testing became popular with the increasing number of IT, office equipment and other items that could be damaged by applying 25A to an exposed conductive part that was earth for functional reasons such as screening.
Historically, high test currents were also used to improve accuracy but modern instruments can give accurate earth continuity measurements using a 200mA test current - it is used in all installation test equipment.
Whislt 25A can in some cases detect cable damage, I am a firm believer in the advice given by the IEE Code of Practice which points at that many faults can be detected by a thorough visual inspection. The visual inspection is often under-valued. If a cable is damaged to the point where the protective earth conductor is suspect, more often than not there are physical signs of damage where the cable has been stressed or runover by a heavy piece of equipment.
High current testing can under certain circumstances detect damaged cables but the cable has to be severly damaged and the test duration has to be long enough to 'fuse' the remaining strands. I did some experiments on a 48 strand cable using a 25A test for 5s. With 42 strands cut i.e. only 6 remaining the cable could repeatedly carry 25A for 5s and so a high current earth test would not have detected the fault.
Low current testing became popular with the increasing number of IT, office equipment and other items that could be damaged by applying 25A to an exposed conductive part that was earth for functional reasons such as screening.
Historically, high test currents were also used to improve accuracy but modern instruments can give accurate earth continuity measurements using a 200mA test current - it is used in all installation test equipment.
Whislt 25A can in some cases detect cable damage, I am a firm believer in the advice given by the IEE Code of Practice which points at that many faults can be detected by a thorough visual inspection. The visual inspection is often under-valued. If a cable is damaged to the point where the protective earth conductor is suspect, more often than not there are physical signs of damage where the cable has been stressed or runover by a heavy piece of equipment.
ABC Technical
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I agree, the "Visual Inspection" is the most important part of any PAT work carried out.
Doc Hudson
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Hello Jimw, welcome to the forum, thats a very helpful & informative first post, (set yourself a high standard to follow), Thank you.
Doc H.
Riggy
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Visual inspection, when done thoroughly, with an experienced eye is the most important test. It is rare for an item to pass the visual and then fail another part of the test. Back to the original point, 25A should always be used unless there's a good reason not to. Although I did wreck a nearly new iron the other day! 
