PAT TESTING EXAMPLES
Examples of PAT testing Class 1 and Class 2 appliances and power cords
During PAT Testing, different tests are carried out depending on the Class of equipment. PAT Testing of appliances is slightly differently to that of power cords. This article looks at some examples of PAT Testing.
If the appliance does not have a rating plate then it is failed straight away. The lack of a rating plate presents the tester with many problems, It is impossible to determine the Class of the appliance, the power taken as well as any approval standards that the appliance has been designed to.
Appliances with a double box symbol are of Class 2 construction. In this case, just the Insulation Resistance test is carried out during PAT testing.
Appliances without the double box symbol are of Class 1 construction and need the Earth Continuity and the Insulation Resistance tests carried out during PAT testing. If the appliance is in a metal enclosure, like an electric fire or a washing machine, then it is relatively easy to clip the Earth Test lead to a metal point. These appliances are classified as Class 2 metal.
Class 1 plastic appliances are totally enclosed in plastic. It is not possible to carry out the Earth Continuity test on these appliances as there is no Earth Point to clip onto. In this case, one needs to do just the Insulation Resistance test when PAT testing is carried out. It is important to make appropriate notes as to why the earth Continuity test was not carried out.
Power cords such as Computer IEC cables or mains extension leads need three tests carried out on them during PAT testing. These are the Earth Continuity, Insulation Resistance and the Polarity test. The latter test checks that the Live and Neutral wires are correctly connected.
Two core power cords do not have an earth. They are for use on Class 2 equipment. They can also be inserted either way round and not polarity sensitive. It is normally only necessary to carry out an inspection on these.
It will be useful at this stage to look at some test examples. There is an example of the different classes of equipment presented below.
Class 2 Test
Examination of the rating plate of a drill confirms that it is built to Class 2 standards i.e. it depends on Double Insulation to provide the two layers of protection to the user. We just need to carry out the Insulation Resistance Test during PAT testing.
The drill is plugged into the PAT tester. The test lead is clipped onto any metal part of the drill. The chuck is a good pint to clip onto. For the test to be effective, it is important to switch the drill on. For this test, there is no mains power applied to the drill so there is no risk of the drill rotating.
On the PAT tester, one simply presses the Class 2 button to carry out the Insulation Resistance test. As this is a Pass/Fail PAT tester one just records the PASS or the FAIL on the Equipment Test Record. If the PAT tester gave an actual test value then this is recorded.
Note: On the run or load available on some PAT testers, power is applied to the appliance. In this case care should be taken that the drill starting to operate does not present any danger to the person testing.
Class 1 (Metal) test
The rating plate on a Burco tea urn indicates that it does not have the double box symbol indicating that it is a Class 1 appliance. This means that it depends on a combination of insulation and an earth connection to protect the user from an electric shock. During PAT testing we need to carry out the Earth Continuity and Insulation Resistance test.
The kettle is plugged into the PAT tester. The test lead is clipped onto the heating element inside the kettle. If there is a lot of scaling, then rotate the clip a few times for it to break through this and make a good contact with the element.
If the kettle has a flat plate then clip onto a screw driver and use this to get a good contact.
It is important to switch the kettle on before carrying out this test. For this test, there is no mains power applied to the kettle so there is no risk of the kettle working.
On the PAT tester, one simply presses the Class 1 button to carry out the Earth Continuity and Insulation Resistance tests. As this is a Pass/Fail tester one just records the PASS or the FAIL on the Equipment Test Record. If the tester gave an actual test value then this is recorded.
Note: On the run or load available on some PAT testers, power is applied to the appliance. In this case care should be taken to add some water to the kettle to prevent the safety cut-out from operating.
Class 1 (Plastic) test
The rating plate of an electric fan clearly indicates that it is a Class 1 appliances. Not only is the double box symbol missing, but there is a clear warning stating that the appliance must be earthed. This means that we need to carry out the Earth Continuity and Insulation Resistance tests during PAT testing.
However, in order to carry out the Earth Continuity test one needs to clip onto a metal part of the appliance. As this fan is completely covered by plastic, there is no place to clip this lead onto. This means that when we try and carry out the Earth Continuity test the appliance will fail.
It is important to appreciate that as this appliance is Class 1 and is entirely covered in plastic it is actually quite a lot safer than Class 1 (metal) appliances. If the live wire inside the appliance were to come loose, the user is still protected by a layer of plastic insulation.
The recommended way to treat a Class 1 (plastic) appliance is to carry out just the Insulation Resistance test. If this is a PASS, then the appliance is passed with a note to state that the Earth Continuity test could not be done due to the plastic construction.
On the PAT tester there is a dedicated Class 1 (plastic) button. When this is pressed just the Insulation Resistance is carried out.
Testing Power Cords
Many modern testers have a handy power cord testing feature. All one has to do is to plug both ends of the cable into the PAT tester and press the Power Cord button to carry out the test. The tester will carry out the Earth Continuity, Insulation Resistance and Polarity test and display a PASS or a FAIL.
This test can easily be adopted to test mains extension leads with the use of a short (20 to 30 cm) IEC lead. A short lead is used to keep the resistance that it adds to the measurement as low as possible.
This is plugged into the mains extension lead and also into the PAT tester. Now when the Power Cord button is pressed the Earth Continuity, Insulation Resistance and Polarity tests are carried out and a PASS or FAIL is displayed. It is important to test all four sockets in the extension lead.