Know the Code
With a revised version of the IET Code of Practice for portable appliance testing expected in January, Jim Wallace of Seaward highlights the main changes in the new IET Code.
The IET Code of Practice for In-Service Inspection and Testing of Electrical Equipment provides a guide to those with a responsibility under the Electricity At Work Regulations 1989.
By providing comprehensive guidance on periodic inspection and testing it ensures that organisations, administrators and those carrying out the testing fully understand the requirements of the EAWR 1989 and can demonstrate compliance with it.
Recently the IET has reviewed the Code of Practice and is in the process of publishing its 3rd edition to take into account technology advances and the implications of other market changes in relation to in-service electrical safety testing.
By expanding the Code of Practice by over 50 pages, the revised publication provides much clearer guidance on all aspects of portable appliance testing with the addition of a number of useful illustrations.
As an example, while the previous document provided detailed advice on checking mains plugs and cables, the revised version is supplemented by the inclusion of multiple illustrations showing typical faults that might be encountered. Similar clarification and added details are provided for all aspects of the inspection and test process.
However, as well as the inclusion of many more informative diagrams, some of the main changes in the updated IET Code concern new requirements in relation to RCDs. In particular the revised version stipulates that when an extension lead or multiway adaptor is fitted with an RCD, the operation of the RCD should be checked using an RCD test instrument to determine that the trip time is within specified limits.
For those responsible for carrying out portable appliance testing this may require some changes to be made to the type of test instruments used. However, Seaward has anticipated these changes and many of the company’s testers are now equipped with an RCD trip time test.
The other area of significant change in the latest IET Code of Practice is in the area of insulation testing. Testing insulation resistance at 500V d.c. can be problematic when the equipment under test is fitted with transient suppressors or mains filtering and until now the only alternative was to perform a protective conductor/touch current measurement. The revised Code of Practice introduces two new test methods which can be used as an alternative to the 500V insulation test. The first method is to reduce the insulation test voltage to 250V dc and the second is to perform an alternative/substitute leakage measurement.
Alternative or substitute leakage is measured using a technique similar to that used when measuring insulation resistance. A test voltage is applied between both live conductors (phase and neutral) and the protective conductor (earth) during a Class I test or a test probe connected to the equipment enclosure during a Class II test. The resultant current is measured and then scaled to indicate the current that would flow at the nominal supply voltage.
The test voltage is 50Hz AC and normally in the range of 40V to 250V. The test voltage is current limited and so there is no hazard to the test operative. As the test voltage has the same nominal frequency as the mains supply the leakage paths are similar to those found when the equipment is in operation. Similarly, because the test voltage is not greater than the nominal supply voltage of the equipment under test, measurements are not affected by transient suppressors, MOVs or other voltage limiting devices.
On a more general note, it has always been recognised that the PAT equipment used for testing should be calibrated annually or in accordance with manufacturers’ instructions. A calibration certificate is issued which states that the test instrument is within specification at the time the calibration is performed.
The certificate does not guarantee the performance of the test equipment at any time after that and the revised IET Code of Practice now recommends that test equipment is checked at regular intervals using a verification device such as a PAT Checkbox. In addition, a record of the performance checks taken should also be kept and the revised document includes a specimen test instrument record form.
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