Why Does the Leakage Test Sometimes Fail on Computers and Other IT Equipment?
The leakage test often causes difficulties for PAT Testing IT equipment, and in many cases, of course, it’s better sometimes to leave out the leakage test as just concentrate on the insulation test value.
However, if you carry out a leakage test on a computer equipment, then you may get a ‘FAIL’ coming up on your machine. It’s not always a correct interpretation, however.
According to the IET Code of Practice for In-Service Inspection and Testing of Electrical Equipment, the pass value for a Class 1 leakage test is a maximum of 0.75 mA for handheld equipment, but 3.5 mA for other Class 1 appliances (including IT equipment.) The problem arises because the PAT Tester has no way of determining whether the appliance is hand-held or not, and so it defaults to the lower setting of 0.75mA.
It is not unusual to find IT appliances which have a small amount of leakage current down the earth wire in normal operation, and in some cases this may be slightly more that 0.75 mA – obviously not enough to cause a problem (and less than the 3.5 mA pass value defined by the IET) but more than the very strict limit set by the PAT Tester.
Therefore, as long as we get a measured value of less than 3.5 mA on the leakage test, we know that the appliance is ok.
Some testers have the Pass Value set at 0.75mA – including the Kewtech KT71 and KT72 and the Seaward Primetest 100.
More advanced testers allow the user to change the Pass setting – the Seaward Primetest 250 allows the user to change the leakage pass value from 0.75 mA to 3.5 mA.
Please note that the leakage test is now referred to ‘touch current test’ on a Class 2 appliance, and the ‘protective conductor current test’ on a Class 1 appliance, although most PAT Testers still refer to the ‘leakage test’ and so I’ve used the latter term in this short article.
There is more information about the leakage test in this article here:-