HomeFlash Testing and PAT Testing: Is a Flash Test Required?
Flash testing is one of those terms that still causes confusion in PAT testing. Some older portable appliance testers include a flash test function, and older training material may refer to flash testing alongside other electrical safety tests. This can lead people to wonder whether a flash test should be carried out as part of routine PAT testing.
The short answer is no. Flash testing is not normally carried out during in-service inspection and testing of electrical equipment, commonly known as PAT testing. It is generally associated with manufacturing, production testing or specific testing after repair, where the correct procedure, equipment and competence are in place.
What is a flash test?
A flash test is also known as a dielectric strength test or hi-pot test. It applies a high test voltage between live parts and accessible conductive parts, or between different parts of the electrical insulation system, to check whether the insulation can withstand the applied voltage without breakdown.
On PAT testers that include a flash test function, the test voltage is typically around 1,500V AC for Class I equipment and 3,000V AC for Class II equipment. These are much higher than the 500V DC normally used for an insulation resistance test, which is why flash testing places significantly more stress on the insulation.
Because of the high voltage involved, flash testing is not simply a more thorough version of an insulation resistance test. It places additional stress on the insulation and can be unsuitable for many types of equipment, particularly modern equipment containing electronic components, filters, surge protection devices or sensitive control circuits.
Is flash testing part of PAT testing?
Flash testing is not normally part of PAT testing. PAT testing is concerned with the safety of electrical equipment while it is in service. The normal process is based on a visual inspection and, where appropriate, electrical tests such as earth continuity, insulation resistance, protective conductor current, touch current, substitute leakage or polarity testing.
The tests selected should be appropriate for the type of equipment, its construction, its class of protection and the environment in which it is used. For many items, the visual inspection is the most important part of the process. In some cases, a visual inspection may be sufficient on its own.
Has flash testing ever been required by the IET Code of Practice?
Flash testing has never been a standard requirement for routine in-service inspection and testing in the IET Code of Practice. The confusion usually comes from the way early editions of the Code dealt with production and manufacturing tests.
The 1st, 2nd and 3rd editions of the IET Code of Practice included information about manufacturing and production testing in an appendix. This section was not part of the main in-service inspection and testing procedure. It explained that production tests could be more arduous and were generally intended for equipment in as-new condition, or for repaired equipment where appropriate.
This meant that flash testing appeared in the wider Code of Practice material, but not as a normal PAT test for equipment already in use. It was included for those dealing with as-new, manufactured or repaired equipment, not as a routine test for everyday in-service inspection and testing.
The 3rd edition made the position clearer. Section 10.5 stated that dielectric strength testing, also known as flash or hi-pot testing, is not normally carried out during in-service testing.
The 4th edition removed the production testing section from the appendix and strengthened this advice further. Section 15.4 stated that equipment should not be subjected to dielectric strength testing because it may damage insulation and may indirectly damage low-voltage electronic circuits unless appropriate precautions are taken.
The same advice is carried forward in the 5th edition, where section 10.4 gives the same warning about dielectric strength testing, insulation damage and possible damage to low-voltage electronic circuits. We cover other important updates in our article on changes across the different editions of the IET Code of Practice.
Why does some PAT testing equipment include a flash test?
The confusion also comes from the history of PAT testing instruments. Early portable appliance test instruments were closely related to equipment used for manufacturing and production testing, so some included a flash test function.
This does not mean that flash testing should be included in a routine PAT test sequence. A PAT tester may contain test functions that are not suitable for every item of equipment, and the person carrying out the inspection and testing must select the appropriate tests for the equipment being inspected.
Why is flash testing avoided during routine PAT testing?
Flash testing is avoided during routine PAT testing because it can stress the insulation of the equipment. Repeated flash testing may weaken insulation or damage components, especially where the equipment was not designed to be tested in that way after manufacture.
Modern appliances often contain electronic controls, filters, capacitors, surge protection components and power supplies. A high-voltage flash test can give misleading results or cause damage if the test is not appropriate for the design of the equipment.
This is why flash testing should only be carried out by someone who understands the equipment, the relevant standard or repair procedure, the correct test voltage, the permissible leakage or breakdown criteria, and the precautions needed to avoid damage. We discuss this wider issue in more detail in our article Can PAT Testing Damage the Equipment Being Tested?.
When should a flash test be performed?
Although flash testing is not normally part of PAT testing, there are situations where a dielectric strength test may be required. These are usually outside the scope of routine in-service inspection and testing.
One example is after certain types of internal repair. If an appliance has been dismantled, rewired, had safety-critical insulation disturbed, or had internal electrical components replaced, further testing may be needed before it is returned to service. In some cases, the repair procedure or relevant product standard may require a dielectric strength test.
This is different from routine PAT testing and minor repairs. Replacing a damaged plug or fuse does not mean a flash test is required. The need for flash testing depends on the type of repair, the appliance construction, and the relevant test procedure.
Flash testing may also be required when manufacturing, assembling or selling electrical equipment. Someone making electrical products for sale needs to consider the relevant product safety requirements, applicable standards and conformity assessment process. This may include appropriate production testing, which can include dielectric strength testing depending on the product and the standard being followed.
This is particularly important for people who make or modify electrical items for sale, such as lamps or decorative lighting. These items are not simply being PAT tested as existing appliances; they are being placed on the market as electrical equipment. You can read more about this in our article on the requirements for making and selling lamps.
Summary
Flash testing is not normally carried out during PAT testing and has never been a standard requirement for routine in-service inspection and testing in the IET Code of Practice.
The confusion comes partly from early editions of the Code of Practice, which included production testing information in an appendix, and partly from older PAT testers that included flash test functions. This led some people to associate flash testing with PAT testing, even though it was not part of the normal in-service test procedure.
For routine PAT testing, the correct approach is to carry out a suitable visual inspection and select the appropriate electrical tests for the equipment being inspected. This may include earth continuity, insulation resistance, protective conductor current, touch current, substitute leakage or polarity testing, depending on the equipment. You can read more about the general inspection and testing process in our guide on how to PAT test electrical equipment.
Flash testing is more closely associated with manufacturing, production testing and certain post-repair test procedures. Where a flash test is required, it should only be carried out by someone who understands the equipment, the relevant standard or repair procedure, and the risks involved in applying a high test voltage.