Portable Appliance Testing Why do we PAT test?We all use a large variety of electrical Earthing – If the outer casing of electricalequipment each day. If all this equipment was equipment is made from a conductive material,used in accordance with the manufacturer’s it is usual practice that it would be bonded toguidelines, it would most likely to be safe during earth. The purpose of this is that under faultits working life. However, this is not always the conditions, a large current would flow to earthcase. A lot of equipment is not treated as the via the casing and the circuit protective devicemanufacturer intended; rough handling, poorly (CPC) tripping/ blowing the protective device.trailing mains leads and often used in the wrongenvironment. These are just some of the Appliance Classificationcommon reasons why electrical equipment failsearly on in its life. The class that the appliance is put in canDue to these facts, we need to implement a identify the line of safety used.preventative maintenance programme. Weneed to prevent injury from faulty equipment, Class I: Any exposed metalwork is ‘bonded’ towhether it is by electrical shock, by mechanical the supply earth. An earth symbol can often beinjury or even fire. To reduce the chance of marked on a Class I appliance. Examples ofproblems arising from faulty equipment, we Class I appliances are fridges, toasters andneed to: kettles. Regularly check equipment for electrical or mechanical faults Review intervals between inspection and test Promote good record keeping Ensure equipment is suitable for the environment it is being used in Encourage users to visually check equipment and report faults. Class II: These rely on two lots of insulation to protect the user. That is, any metalwork that theThe Electricity at Work Regulations (EAWR) user may touch, which may potentially becomedoes not require inspection and testing and they live, is separated from any dangerous voltagesdo not specifically mention portable appliances. by two distinct layers of insulating material.However it does state that all electrical systems These appliances do not have an earth leadneed to be maintained to prevent injury and fitted. Examples of Class II appliances would bedanger. In summary, as danger is defined as lawn mowers, hedge trimmers and table lamps.“risk of injury”, if there is the slightest of faults Below is the symbol that should be displayed onwith the equipment that could have been Class II appliances.prevented with regular maintenance, you couldfind yourself in serious trouble.There are two main lines of defence in the safeuse of electricity:Insulation – Providing adequate isolation fromlive electrical parts so the user does not comeinto direct contact with them, preventing Some appliances use a combination of theseelectrical shock. Insulation should have very two methods, often called ClassI/ClassIIhigh resistance. appliances.
Essential tests that should be carried out when There are some optional tests, which may betesting portable appliances are: performed once the essential tests have been Visual Inspection completed. These tests are not always available Earth Bond Test (Class I appliances as standard on all PAT testers. only) Insulation Test Flash – not to be routinely carried out and should only be performed by fully trained personnel, due to high voltages used. Flash testing can stress the appliance therefore ifVISUAL INSPECTION performed regularly; flash testing couldThis test is the most important test. Statistics deteriorate the insulation. Flash testing wouldhave shown that it reveals approximately 90% typically be used when an appliance has beenof faults on portable appliances. Visual completely overhauled or at manufacture.inspections can be carried out on three differentoccasions: Load and Operation – can be useful for routine User Checks – visual checks carried out testing. The portable appliance tester will run by user. Records are only kept if faults the appliance for a pre-determined amount of are found. time. During this time, it will typically carry out Formal Visual Inspections – carried out two tests: by a competent person. All results are Load – During the test, the tester will logged. check the rating (in VA) of the appliance. Combined Inspection and Testing – This can be a useful early indicator of carried out by a competent person. All mechanical wear, such as worn results are logged. bearings. Touch Current Test (earth leakage) – very good substitute if there is any doubtEARTH BOND TEST whether an insulation test can beTo ensure any exposed metalwork on the applied. The test compares how muchappliance is securely connected to earth. During current is flowing in the live wire againstthe test, a high current (typically 25A) is passed what is flowing in the neutral. Anythrough a circuit comprising the appliance earth difference must be leakage to earth;conductor of the supply lead, the exposed regardless of what path it takes.metalwork and the tester bond lead. If theconnections are good, the resistance of thecircuit will be low. Testing should be systematically documented with all the results recorded. Whether this is byINSULATION TEST test sheets or software packages. EachTo ensure that a breakdown of the insulation appliance should be clearly labelled with thecannot occur between any live parts within the next test date being displayed to ensure testingappliance and parts of the casing that the user is done at the due time.may touch. The appliance tester must becapable of performing a 500V d.c test acrossload resistances of 2MOhm and greater,otherwise the test is invalid. This test can beperformed as many times as you like withoutcausing undue stressing to the appliance undertest.
Below is a table showing the portable appliance testers Megger have to offer. PAT 32 PAT4DV PAT4DVF Functions Fuse check ■ ■ ■ Circuit test ■ ■ ■ Insulation ■ ■ ■ 120V appliances ■ ■ 230V appliances ■ ■ ■ Extension lead test adaptor option option option Earth continuity ■ ■ ■ 10A Earth bond ■ ■ ■ 25A Earth bond ■ ■ ■ Operation test ■ ■ Lead test ■ ■ Flash test ■ Earth leakage ■ ■ Test sockets BS1362/BS4343 (UK) ■ ■ ■ Features Automatic operation ■ ■ Client/Location/Results database ■ ■ RS232 download ■ ■ Printer port ■ ■ Full keyboard ■ ■ Digital display ■ ■ ■ Backlight ■ ■ Bar code reader option option Results printer option optionPAT_AP_EN_V01