Posted By Graham Sargeant I'm sure everyones aware of the requirement to test portable appliances, I work with a tool hire company and we test equipment every hire, the grey area we have is with flash testing as part of the appliance test. I cannot find a reference that states we must flash test every time, so we've adopted a policy of testing earth bond and insulation every hire (along with the usual visual checks) and flash test every 3 months, is this acceptable or are we in breach of any duty/regulations. Thanks for your responses.

Posted By Jim Walker Dielectric strength tests, flash test to you, can indeed over stress circuits. Anything that contains semiconductor devices including IT equipment is unlikely to survive repeated flash testing. I once witnessed someone destroy the control room of a major UK oil refinery with indiscriminate flash tests Generally the test is only done following a repair or if you suspect the machine is unsafe. This is why a competent person (ie not a PAT tester button presser) is required to carry out inspection and testing. Personally I think too much emphasis is placed on electrical results and not enough on what a suitably competent person would see and deduce. Note also that done incorrectly the flash test can be hazardous to the test operative. This is particularly so with Class 2 double insulated equipment. I work in an electrical manufacturing environment where all equipment needs flash testing and our controls are very strict because of this. You say you are a hire shop as a rule of the thumb I would flash test anything with an electric motor every three months possibly more if the machine has had some stick. If you contact Megger or Seward they will send you some very helpful booklets. See also HSG107 (essential reading) and INDG236 both from HSE books

Posted By Nigel Singleton BSc The 'Code of Practice for In-service Inspection and Testing of Electrical Equipment' produced by the Institution of Electrical Engineers states in section 10.4 (in bold text) Dielectric strength testing is not normally carried out during in-service testing. On the PAT course that I attended, the instructor informed us that 'flash testing' was no longer 'in vogue' and should only be conducted in extreme circumstances, as it invariably damages or weakens the appliance being tested. In many cases it leads to complete destruction. The electricity at work Regs, do not require PAT testing to be conducted at all, they state that electrical equipment must be maintained in an efficient manner. PAT testing is only one means of checking the efficient manner.

Posted By Colin Brayshaw.LicCIPD Hi Graham Sorry about the delay in responing! Information on Flash Testing The flash test, also referred to as “HI PoT”, “Dielectric Strength” or “Insulation Breakdown” test is intended to verify that creepage distances, clearance distances and insulation levels around live parts, are sufficient to prevent excessive leakage currents causing hazards to the user. As another “core” electrical safety test, this is also a requirement of many National, European and international standards. In application, live parts refer to both the line (Phase) and Neutral supply paths. For test purposes these are joined together to form one test point, with the other test point being the Earth (Protective Conductor) for class 1 products, or the outer surface of class 2 products. Any function switches on the product should be switched on to include all parts of the supply path. Typical “Type Test” requirements are for a test voltage of between 1,000Volts and 1,500 volts, for class 1 products and (2,500 to 4,200Volts) for class 2 products, to be applied for 1-minute period and for the product to withstand a leakage current level of up to 100mA. For Production line testing, where high throughput is a major consideration, the test period can be reduced to a few seconds by increasing voltage levels by 10%, and at the same time lowering the acceptable leakage current to less than 5mA. This has the added benefit that it makes the test safer for the operator. Most flash tests requirements stipulate that the test voltage should be from an a.c. source, with a substantially sinusoidal waveform. With the increase in sensitive components within many of today’s products, alterative methods are sometimes called for: These can range from the application of d.c. Voltages (Usually 1.4 times the stated a.c. voltage) to the soft-start. Advantages offered by more sophisticated testers that use programmable ramp profiles for raising and lowering the test voltage. This minimises the rapid rates of potential change that are the main cause of sensitive component failures, not the actual high voltage. It is important to remember that flash testing can be hazardous if improperly applied. And common sense precautions should be taken, such as the use of safety enclosures, well defined test areas and adequate operator training. To test or not? The view that flash testing is a destructive test is often raised in discussion. This largely originates from its use in Type testing laboratories where high voltages are sometimes applied for long durations, with the intention of testing products to destruction. However, in terms of production and routine in-service testing applications, there is little or no evidence to suggest that the short period flash test degrades a product, even after repeated testing. There are many reasons for flash failures, most of which lead back to such things as manufacturing errors, inappropriate materials and designs that fall short of the exacting standards required in today’s safety conscious environment. The flash test doesn’t cause the problems; it merely provides the means to find them. So within the Hire industry you would be wise to Flash test all apropriate appliances. Colin