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- 27 Jan 2008
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I use the clamp-on to measure existing earth leakage, turning off loads yes, but the strain on the terminals can affect the operation of some models, so one should not disconnect at the RCD/RCBO to test, as need to know it will work once terminals are torqued up.RCD/RCBO tests should be done on the breaker it's self with the downstream load/s disconnected to ensure you are not testing with existing earth leakage, and test at 1/2 rating first to ensure it is not tripping prematurely.
Using the ramp test, if available, does show how much to spare. We used to do 6 tests, but that has been reduced, I am not sure why? I still tend to do positive and negative half cycles.
But I blame poor testing on the forms, if the form does not ask for line - neutral loop impedance or prospective short circuit current then people will not test it, so we have no idea of the volt drop of the circuit.
I was taught to test for figure of 8, but I can not find a regulation which says you can't have it. But after being qualified, and had already done as then 16th edition and PAT testing, the C&G 2391 was a further 12 weeks one night a week of 3 hours, so 36 hours of training as to how to inspect and test.The test what needs the most attention is that when testing ring final circuits and making sure you are aware you can have "rings" within "rings", by what I mean is sections of the ring final circuit bridged together.
And I failed the installation due to increase of loop impedance was too high for such a short run, and investigated further and found resistors soldered into the wires to emulate a larger installation, however I pointed out had the sockets been used, there would have likely been a fire, so was a valid fail, which left him with a problem, what to do with those who had not found the resistors.
Much of the testing is down to what one expects to find, and can't really teach that.
But the LABC inspector has to judge if the person doing the work has the skill required, and he needs to watch his own back, so what he wants is written proof the person has the skill, and a C&G 2391 goes a long way towards that.
