PAT450 portable appliance tester

You can use an adaptor (p/n 35871). Set the port number in the properties of Download Manager to the same port number in Device Manager to ensure the software is looking at the correct port.

The battery may not have enough charge. Try leaving the PAT plugged in for a couple of hours to charge or replace the 9 V rechargeable PP3 battery. Be sure to press the red button when finished testing to prevent the battery from draining.

Hold down the test button while the tester switches on and select reset. Warning: Back up your data before resetting, as data may be deleted in the process.

Although infrequently encountered, when an “E56” message appears, a fuse has blown due to a failure on the programmed board. You can replace fuses and restore operation for a time, but most likely, there is a problem (defective or burnt-out component) on the board. Schedule your PAT450 for calibration or replacement.

Earth continuity is applicable for Class I equipment and extension leads. The purpose of the test is to ensure that the earth terminal has a low resistance connection to the conductive metal casing of the appliance by electrical bonding. Two test methods are available, and the technique used should depend on the circumstances.

• Low current continuity test - A continuity measurement is made with the asset plugged into the PAT tester and using a short circuit test current of between 20 and 200 mA. The test is made between exposed conductive parts of the equipment and the earth pin of the plug (or earth-terminal of the supply). This is performed using the PAT’s earth bond lead. Note the maximum resistance value while flexing the asset supply cable. You should investigate any fluctuation in the reading. You should also visually examine the power cable terminations at both ends.
• High current bond test - A continuity measurement is made with the asset plugged into the PAT tester and using a test current of at least 1.5 times the fuse rating (max 26 A) for between 5 to 20 seconds. The bond test should be made between exposed earthed conductive parts of the equipment and the earth pin of the plug (or earth-terminal of the supply). This is done by connecting the earth bond lead of the PAT to the exposed metalwork. Note the maximum resistance value while flexing the asset supply cable. You should investigate any fluctuation in the reading. You should also visually examine the power cable terminations at both ends.

Take care when measuring earth bond on appliances where the construction includes exposed metalwork having casual contact to earth. This metalwork is primarily protected by double or reinforced insulation. The earth connection is only classed as ‘fortuitous.’ So the resistance value is unlikely to be as low as truly bonded metalwork, and a test performed on this unbonded metalwork may give misleading results. Examples of this construction may include a steam iron’s soleplate or a kettle’s metal chassis. A high current bond test using up to 26 A may also damage casual-contact components. You should perform a low-current test first to identify potential problems.

To pass the earth continuity test, the measured value should not exceed those shown:

If the resistance R of the protective conductor cannot easily be measured, the table below provides nominal cable resistances per metre length for various types of flexible cable.

You should identify the cable and measure its length. You can calculate the protective conductor resistance using the app PAT toolbox or by using the table and a calculator. The Megger PAT400 testers have built-in compensation for resistance in long supply cables.

Generally, you perform insulation testing by applying a known (500 V DC) test voltage and measuring the insulation's resistance. 500 V may cause damage to sensitive equipment such as IT. Therefore, you may substitute with a low voltage (250 V) insulation test, a touch current test, or an alternative leakage current test.

Note: you should not touch appliances during an insulation test. The exposed metalwork may rise to the test voltage if a fault exists.

The test method varies depending on whether the appliance is Class I or Class II. For a Class I test, the appliance is plugged into the PAT tester, and the insulation test is carried out between the earth pin and the plug's combined live and neutral pins. The Megger PAT makes these connections for you.

A Class II appliance is slightly different as there is no connection to the plug earth pin. This time a connection is made between the combined live and neutral pins and any metal parts, dirty or conductive areas of the casing, and may involve several tests. The connection method is the same as that used for the earth bond test, using a test probe.

Note: You must switch on the appliance at its own power switch for both test methods. If it is not, then the electrical test is only being carried out as far as the switch. The minimum insulation readings that you should obtain are shown in the table below. For equipment with an electrically operated switch, the insulation test can be substituted with a mains-powered protective conductor or touch current measurement.

This test is an alternative to an insulation test. We recommend its use when an insulation test could damage the asset or when the insulation test results are suspect. For this test, you energise the asset at its normal operating voltage, and any current flowing to earth is measured. For Class I, this is to the earth pin of the plug; for Class II, this is to any accessible conductive surface using a remote probe. 

Note: a low voltage insulation test should be performed before any energised test, such as the touch current test, to identify any potential danger from poor insulation and shorted connections. This test is only available on the more sophisticated portable appliance testers, such as the Megger PAT.

It is essential to ensure that the asset is safe to run during the test. For example, if testing a kettle, it should be part-filled with water so as not to damage the element during this test.

This test is useful where it may be deemed dangerous to run the asset during a protective conductor or touch current measurement. This test uses 40 V AC, which will not operate the asset during the test. This test can be battery powered, removing the need for a mains supply during testing.

In all cases, the current is measured within five seconds after the application of the test voltage; the values must not exceed those given below.

A functional test is carried out during the “load” test or the mains-powered protective conductor or touch current measurement. This test will determine the following:

1. if the asset functions correctly
2. the VA rating of the appliance

This can be a good indicator of future problems and potential failures in an appliance. Problems, like worn bearings on a drill, would probably result in increased current drawn from the supply and, therefore, an increase in the VA reading.