TEST & MEASUREMENT Electrical safety testing ethos


Having an accredited product safety test report with appropriate certification helps manufacturers to achieve compliance with regulation and requirements in various global markets.


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t may also help them to discover any problems in the product early on and avoid expensive product recalls, as well as reducing the risk of expensive litigation should a product cause injury.


Each test standard for a specific product type will provide guidance as to how its requirements are met with relevant testing and compliance criteria, documentation, and product marking requirements. It is important to note that safety standards require compliance under normal, abnormal, and single fault conditions. Some of the tests might damage a sample, but this does not necessarily mean a non-compliance.


Preparation


The product test laboratory sees many different and often innovative designs each year and may not be familiar with your product, so you must brief them fully on the design, intended use, and operation in advance of testing. In general, this will include: •


Brief description of operation (including temperature, humidity and whether in a clean, dry or wet and/or dirty environment)


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• • •


Marketing material; schematic diagrams, block diagrams, PCB & component layouts & constructional drawings Parts lists/BOMs


User, installation & service manuals


Specifications/details/approval documentation for safety critical components (e.g. batteries, enclosure plastics, PCB material)


These are all key items which will enable the preparation of an accurate test programme. If adequate information is not available prior to the start of testing, it is likely that delays and further costs could be incurred.


In the test laboratory


Working samples must be able to be operated at full load. The laboratory will confirm the number of samples required, and will confirm whether they should be potted, open enclosures or sealed. They may also require representative loads for some outputs. They will also need some safety critical components for strip-down and


measurements, such as unpotted/ unvarnished transformers, alongside components which are likely to be damaged during fault testing and can be easily replaced in the laboratory, such as fuses and leaded components. They will ask you to supply consumables used during testing, such as labels for a label printer.


Samples should be representative of final production. However, if there are any variances, such as 3D printed parts that will be replaced later or different coloured enclosures, these should be disclosed as early as possible. This ensures that any potential impact on testing can be determined to avoid unexpected cost and delays.


The full assessment of a product combines physical inspection, dynamic tests, and documentation review. There are two overall parts to the laboratory testing work, inspection and dynamic tests.


Inspection


The inspection part of the assessment includes examination, measurement and verification. This includes a review of the product’s markings, such as ratings and warnings/cautions, and the instruction manual is also reviewed.


A product will be inspected for creepage and clearances, checking distances between


46 JUNE 2024 | ELECTRONICS FOR ENGINEERS


hazardous parts and accessible parts of equipment. Safety-critical components are tested to ensure they have adequate and current certification, and that they meet the requirements of the relevant standard. Also, any hazardous radiation sources, including lasers and visible light hazards, must meet their required approvals to ensure they are within safe levels in equipment.


Dynamic tests


Dynamic tests include input current checks, which verify that the full-load current or power does not exceed the marked ratings of the equipment. Thermal tests ensure that components operate within their limits. Single fault tests cover a broad range of conditions, including, but not limited to, short circuiting of functional insulation and components.


A high voltage test, such as hipot, electric strength or dielectric breakdown test, usually for mains products, is applied across insulation barriers to ensure that breakdown does not occur. Touch current measurements may also be conducted, which ensure that no hazardous leakage currents are accessible to users or operators. Tests must also be done to check that mechanical hazards are adequately safeguarded.


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