The Kewtech KT71 has a number of interesting features.
For example you may see the message ‘OFF’ followed by a ‘?’ with a red fail indication when doing an insulation test. This is because the tester checks the load (Watts) presented by the equipment which is being tested but it can’t read below about 200 Watts. If the Wattage of the equipment is below this level, for example a 23 Watt battery charger, ‘OFF’ followed by a ‘?’ with a red fail will be displayed; it is not a fault condition, it is only indicating that it can’t see a load and is asking if the appliance is switched off. You simply press the ‘START’ button again and the tester will continue with the test. The usual cause for this display is that you may not have switched the equipment on in which case switch it on and press the ‘START button again.
Sometimes the KT71 will fail a computer on the leakage test. This is due to the tester having ‘Fixed limits’; where there are two limits the tester will test to the lower limit. Table 15.3 on page 77 of the IEE Code of Practice 3rd edition indicates that Portable or Hand Held class I appliances should not exceed 0.75 mAmps while IT, Movable and Stationary class I appliances should not exceed 3.5 mAmps; the KT71 is set to the lower limit of 0.75. For IT, Movable and Stationary class I appliances, as long as the reading does not exceed 3.5 mAmps, you can pass the appliance on the leakage test even though the tester indicates a fail. Just press the ‘START’ button to continue.