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A guide to PAT testers

Jim Wallace of Seaward says that matching the correct PAT tester for the right safety testing application is essential.

The essential role of portable appliance testing (PAT) is to reduce the risk of electric shock by detecting potential safety problems with electrical appliances before they occur.
In this way testers ensure the safety of electrical equipment used in all workplaces and enable employers to meet their legal obligations to provide a safe environment for staff and the public.

PATs start from basic pass/fail instruments capable of carrying out fundamental checks to more comprehensive testers. There are also choices to be made between battery and mains powered testers, those capable of testing to the latest IEE Code of Practice and whether or not test data needs to be recorded for transfer to PC-based records systems. 
The essential tests for most electrical products are earth continuity and insulation resistance, although a host of other tests may also be required depending on the type of equipment in use and the associated risk factors. Given the growth in PAT testing, there is now a wide range of choices available and careful consideration needs to be made in relation to specific user requirements, all round tester performance and, of course, the budget available.

Basic PAT testers
At the basic level, PAT test instruments are available as relatively simple to operate devices that carry out basic electrical safety checks. 
Most are equipped with an earth continuity test, insulation resistance test and the ability to check to wiring of detachable mains cords but do not include tests which involve applying mains power to the appliance under test, for example protective conductor current or touch current. Results are displayed either as an immediate ‘go/no go’ indication – either in the form of a simple digital display and/or a pass/fail warning light, or measured values which can be recorded for traceability. 

These basic instruments do not possess an internal memory for results storage and are designed for use by those who may be relatively unskilled in electrical work or for those who have a relatively small number of appliances to test. 

Intermediate PAT testers
The next level of instruments offer a more comprehensive range of tests and often include measurements such as protective conductor current, touch current and RCD trip time. 
The additional functions allow the user to test a wider range of equipment types in accordance with the IEE Code of Practice - for example, appliances with electronic power switches where insulation resistance testing is not appropriate. 
In the same way, the IEE Code also now recommends a choice of insulation test voltage of 250V DC or 500V DC - or the use of substitute or alternative leakage measurement for some types of electrical equipment. Again not all testers are equipped with the capability to undertake this variety of tests.

Also, in the most modern, tests can also be undertaken to measure protective conductor current in industrial 3-phase equipment using special in-line test adaptors.
In general, these instruments do not possess an internal memory for results storage but give measured values which can be recorded using a paper based system or suitable software package for improved traceability. They are therefore more suited to those who require a wide range of electrical tests but do not require automatic data storage. This may include electrical contractors who may carry out PAT testing as part of more traditional electrical test services. They are also ideal for those who may have an in-house responsibility for ensuring the safety of equipment used premises such as small business premises, schools, service & maintenance staff and local authorities. 

Advanced PAT testers
For more comprehensive test requirements, more sophisticated mains and battery powered ‘downloading’ testers are available that combine user-friendly operation with a whole range of other features for particular test demands or routines. 
These include options for manual or automatic testing (with pre-set pass/fail thresholds) and the ability to reconfigure the automatic test sequences to cater for a wide range of electrical appliance types. As a result, fast throughput testing can be achieved without affecting the integrity of the testing undertaken. 
The more advanced and comprehensive PAT testers also incorporate a suite of other tests that can include protective conductor current, touch current and substitute leakage. 
For these high volume applications, highly portable PAT testers are now available that incorporate all Class I and Class II required electrical safety tests in a lightweight hand held enclosure. In most, long life battery power eliminates the reliance on mains outlets for testing, making the instrument totally portable and suitable for universal testing applications. 
The most sophisticated downloading testers are capable of recording not only the test results but also details of the test program, site and location of the asset under test, details of the operator and the time and date that testing was carried, out all of which can be transferred to PC-held test management programs for complete traceability. 
In addition, some advanced PAT testers also include a special time saving ‘upload’ facility enabling testers to be pre-programmed in advance with details of the appliances to be tested during a particular site visit or test shift.
The integration of test data collected by the PAT tester and computerised record systems also enables various improvements to be made in test scheduling, identifying next test due dates and the development of asset registers. 
Advanced testers are therefore more suitable for use by PAT testing companies and specialist facilities management service companies with large asset databases under their responsibility.
For all of these reasons, the careful selection of the correct PAT tester for the required application is essential. Given the wide choice available, the use of the most appropriate PAT tester can significantly improve operational efficiencies for both in-house testing and PAT companies – and ensure the provision of competitive and value-added service to customers.

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