The schematic Diagram A is another Class 1 appliance in this instance a modern ‘electronically controlled’ washing machine. Unlike the kettle this appliance has far more internal components and more importantly has a more complex wiring and operating system. As before the three core mains lead connects to the appliance and in this instance passes through a suppression unit marked ‘IF’ (interference filter) before continuing on to the main control circuitry (PCB). If you look closely at the top left of the board the L & N terminals connect to two ‘Normally Open’ relay switches in circle 1 i.e. they do not ‘close’ mechanically as with a rotary or simple push On and push again for Off type mains switches. These PCB mounted ‘relay switches’ can only close when instructed to do so i.e. when a programme has been selected and the ‘start’ (low voltage) selection button is pressed. NOTE: This action ’cannot’ be carried out when using a basic PAT tester for insulation testing. Therefore an insulation test on this type of circuitry using a basic PAT tester is unable to go beyond the two ‘Normally Open’ relay switches which means that critical components such as the heating element, wash motor etc. are not tested. In such cases the applied test essentially only tests the plug, the mains lead, the suppression unit and the two wire up to the main control board. Although there are methods of compensating for this type of situation it takes knowledge of the product and additional equipment as most PAT testers are unable to test individual components (but some top end ones can).
Editors Note – Once again, in terms of depth of knowledge, consumers should be able to recognise and trust an independent standard, such as EEESafe, to ensure purchased repairs or reuse appliances carry a lower risk of an accident or an early failure occurring. This is particularly important when the item has been re-introduced from being designated as waste, tested by a protocol and uncertified Appliance Repairer. (PAS141)
There are a wide range of PAT test meters available and some are capable of applying a range of additional tests such as “Earth Leakage”, “Touch Current” and “Sub Leakage (note: this last test does not power up the appliance)” which are essentially variations of ‘Run’ testing. Such a range of test options (or not) can in itself lead to further confusion during PAT Testing or when comparing different PAT Testing equipment. Such tests essentially allow the appliance to be operated via the PAT test meter. Unfortunately this type of test on many PAT test meters is often restricted to a rather short period of time (often only a few seconds) as most PAT test meters are not designed to power appliances for extended periods of time. Such a short period time allotted for testing may not allow the door interlock mechanism to fully energise before the ‘timed’ ‘run’ period ends.