PAT Testing for Earth Continuity
The Earth Continuity test is carried out on all electrical appliances which are classified as Class 1. The main aim is to make sure that there is a correct link between the housing of the appliance that houses the device and the Earth pin of the plug. Upon testing if the resistance is less than 0.1 Ohms or 100 milliohms ,the connections is considered as a good connection.
Sometimes the Earth Continuity is called the Earth Bond test or the Earth Resistance test. They all test the quality of link between the plug of the mains and an Earth point. The standard method to carry the test is to connect the appliance into a Tester, and then clip it to the Test lead to an appropriate earth point.
After the test has been completed and the resistance measured to be less than 0.1 Ohms, then there is a strong earth connection, and the device is considered to be to be safe. While conducting the test for PAT testing There are a lot of things that should be considered.
Earth Point on Appliance
To carry out the test, it is crucial to make sure to clip the test lead at a suitable earth point. If this isn’t done, then there will be no route for the current to be used during PAT testing. This could cause the appliance to fail the test.
The best earth point can be achieved through years of experience. It is vital to have an excellent connections to an Earth point. The corrosion of the metal or the scaling on kettle components can prevent the connection from being low resistance. If this is the situation, then turn the connector upside down and make use of those teeth in the clip remove the scale or rust to ensure a strong connection. It is also possible to use a screwdriver as a clip and then connect with an Earth point.
The Golden Rule when testing Earth Continuity If you failure at first, don’t immediately stop the device. Be sure to have an adequate connection before you attempt PAT testing over and over. If needed, you can try another Earth point, as there are many metal parts that may connect to the earth.
PAT test — Class 1 plastic appliances
On certain Class I appliances, it might make it difficult to reach an earth point outside in the event that the appliance is covered with plastic. There are, for instance, several electric fans which fall in this category. This poses problems because in the event that we can’t attach the tester lead with an earth point there’s no circuit created so it is likely that the Earth Continuity test will fail.
When it comes to these appliances, it’s important to note the fact that their design creates a safer environment than traditional metal appliances of Class I. Along with possessing the Earth link, the appliances have a plastic enclosure, giving them an additional layer of security. The method to conduct PAT tests on these devices is to continue to perform an test of Insulation Resistance Test. If it passes, note this test in the Equipment Test Record and make an observation that the test for earth continuity was not able to be conducted because of the enclosure’s plastic.
PAT Testing Test the current
The person conducting the test may choose either of the choices below.
Option 1: Apply the test current to be 1.5 times the amount of fuse within the plug to 25A. For instance, when testing a kettle that has 13A fuse the test current should be 25A is recommended. If you are testing a lamp with a 3A fuse the test current should be approximately 4.5A is utilized. The current is usually applied for between 5 to 20 minutes. This test should not be performed on IT or any other equipment in which electronic components are used. The huge currents that flow through the earth conductor are identified to trigger surge voltages which have caused damage to electronic components.
Option 2: Apply the test current to be between 20 to 200 mA. When the test is completed, the cable needs to be bent to reveal any obvious flaws. This test is extremely safe and can be performed on ALL Class I devices, including IT equipment.
PAT Testing Test Limits
As stated above, in order to pass the test , the Earth Continuity resistance has to not exceed 0.1 of an ohm when the PAT test is performed. Because this is measured from the plug’s pin towards the Earth point, a provision is created for the Mains lead which is attached to the appliance. For instance, a Class I lamp comes with a 5m mains cable (current capability of 3A) connected to it. This leads to a total resistivity of the cable can be 0.195 ohms. On top of that, one could add the 0.1 Ohms of the appliance, giving an amount of 0.295 Ohms. If you test this lamp to determine earth Continuity and it was 0.22 OHM, then it could be able to pass the device. For example, a computer has five meters of cable with capacity 13A at present. The resistance total of this cable is 0.078 Ohms. The limit of pass for this device is 0.1 + 0.078 which equals 0.178 ohms.
If the appliance is equipped with a short mains cable, it is not a significant contributor in the resistance to earth. For instance, a cable of 1m to an electric fireplace has an earth resistance of 0.015 Ohms. If you are using a PAT Tester with an LCD that shows the test results, the user can figure out if the device is successful or not, considering all the distance of the mains lead into consideration. For PAT Testers that pass or fail that are equipped with a display, there is an automatic allowance for the mains cable. The standard limit is set to approximately 0.25 Ohms to accommodate five meters of cable. On certain PAT Testers, such as Pass/Fail PAT Testers, room may be made for longer cables, for instance when testing 20m or 10m extension leads.
