What is Portable Appliance Testing and Why is PAT Test Done

Published by Carelabs, Carelabs is authorized provider of Electrical Installation’s Study, Analysis, Inspection, and Certification services in UAE. Website: carelabz.com


Image: Carelabs – PAT test

Portable appliance testing (commonly known as “PAT”, “PAT Inspection” or (redundantly) as “PAT Testing) is the term used to describe the examination of electrical appliances and equipment to ensure they are safe to use. The formal term for the process is “in-service inspection & testing of electrical equipment”. Most electrical safety defects can be found by visual examination but some types of defect can only be found by testing. However, it is essential to understand that visual examination is an essential part of the process because some types of electrical safety defect can’t be detected by testing alone. 

It’s a myth that all portable electrical appliances in a low-risk environment, such as an office, need to have a portable appliance test (PAT) every year. The law simply requires employers to ensure electrical equipment is maintained in order to prevent danger – it doesn’t state what needs to be done or how often. 

The frequency of inspection and testing depends upon the type of equipment and the environment it is used in. For example, a power tool used on a construction site should be examined more frequently than a lamp in a hotel bedroom. For guidance on suggested frequencies of inspection and testing, see: Maintaining portable and transportable electrical equipment. 

Why PAT is Done? 

The key word is liability. An employer or manufacturer should show as much concern about safety as does the legal system. The liability is with the employer or owner of a place of business, or public place, to ensure that all electrical equipment accessible by employees or the public is maintained in a safe condition. The liability is with the manufacturer of electrical equipment to ensure that the equipment is safe for those who operate it. The best way to ensure electrical safety is by routine visual examination, electrical testing and documentation. 

The NFPA standard states that “Electricity is widely recognized as a serious workplace hazard, exposing employees to electric shock, burns, fires, and explosions. Underlying causes are listed as work involving unsafe equipment and installations, workplaces made unsafe by the environment, and unsafe work performance. Hazards stemming from faulty equipment are further identified as faulty insulation, improper grounding, loose connections, defective parts, ground faults in equipment, unguarded live parts, and underrated equipment.” 

Health and safety regulations require that electrical appliances are safe and maintained to prevent harm to workers. Many equipment manufacturers recommend testing at regular intervals to ensure continual safety; the interval between tests depending on both the type of appliance and the environment in which it is to be used. Some equipment is just more likely to sustain damage than others. Handheld types are handled and moved more than other types and this can lead to rough handling, which often results in damage and early life failure. The legislation deems that any competent person can perform it by using a PAT instrument or tester. The visual examination of each appliance in addition to the actual PAT test should be performed only by someone who is deemed competent. 

Testing equipment has been specifically developed for PAT inspections, based on the testing equipment used by manufacturers to ensure compliance with the British Standard Code of Practice and European product standards relevant to that type of appliance. This in turn allows testing and the interpretation of results to be de-skilled to a large extent (citation needed). The inspection of the appliances can largely be carried out in-house in many organisations. This can result in cost savings and more flexibility as to exactly when a PAT is carried out. 

What is Done During PAT? 

A relatively brief user check (based upon simple training and perhaps assisted by the use of a brief checklist) can be a very useful part of any electrical maintenance regime. However, more formal visual inspection and testing by a competent person may also be required at appropriate intervals, depending upon the type of equipment and the environment in which it is used.  

Testing involves a visual inspection of the equipment and any flexible cables for good condition, and also where required, verification of earthing (grounding) continuity, and a test of the soundness of insulation between the current carrying parts, and any exposed metal that may be touched. The formal limits for pass/fail of these electrical tests vary somewhat depending on the category of equipment being tested. 

PAT can be done by hiring an external company, like Carelabs, to test all the electrical products in a business or it can be done in-house by a competent person. In a low-risk environment most dangerous defects can be found simply by checking the appliances for obvious signs of damage such as frayed cables. 

The dangers of contact with live electrical parts need no explanation to an electrician. However, the environments in which the majority of portable appliances are used are not necessarily where operators would be aware of the dangers or the implications of damage to equipment. The point of routine visual inspection and electrical testing is to identify potential hazards and actual dangers before they turn into an accident.  

The hazards that must be identified include:  

  • Personal exposure to live conductors — electrocution.  
  • High current faults causing excessive heat — fire.  
  • Intermittent connection — arcing causing heat and potential ignition.  

These hazards can be identified by performing in-service:  

  • Regular electrical tests.  
  • Visual examination.  
  • Combined visual examination and electrical tests. 

Various people have responsibility for electrical equipment, including:  

  • Property owners, equipment owners, company owners, directors, and line managers etc.  
  • The person undertaking the formal visual examination and electrical testing.  
  • Maintenance managers.  
  • Operators of the equipment. 
What Needs to be PAT Tested? 

Determining what needs to be PAT tested is not as difficult as it sounds. For the purpose of legislation, portable appliances include all equipment that is not part of a fixed installation but is meant to be connected to a fixed installation or generator. Any appliance that uses a flexible cable or plug and socket qualifies as a portable appliance. In other words, if you have an appliance that has a plug that is intended to be connected to a wall socket or generator, it qualifies as needing to be PAT tested. 

This can include items such as electric drills, monitors, printers, PCs, kettles and larger items like photocopiers, vending machines and others. So a cordless power tool would not need to be PAT tested but their battery chargers that plug into the wall for power do need to be tested. 

All IT equipment should be tested, including power cords to this equipment although they are required to be tested separately from the equipment that they power, because they are held to a different standard. Electrical cable extensions are the most commonly tested items as they are among the most common sources of safety hazards. All of your 110 volt equipment in addition to all 3 phase equipment should also be tested. 

PAT Testing Regulations 

Conforming to PAT testing regulations will help you to ensure that the portable appliances in your business are safe and help you to avoid violations. PAT testing legislation was put into effect to ensure that all companies conform to the Health and Safety at Work Act of 1974, Electricity at Work Regulations of 1989, Provision and Use of Work Equipment regulations of 1998 and the Management of Health and Safety at Work regulations of 1999. 

The current law requires that all employers maintain portable appliances and ensure their safety. PAT testing law requires that all landlords, employers and even self-employed individuals make sure that their portable electrical appliances are safe and are suitable and used for the purposes intended. These appliances should always be maintained properly and remain in good working order. 

The guidelines are designed to make certain that this equipment is kept protected and is preserved through regular maintenance as well as inspections and periodic testing. Damage and fault can occur with all electrical equipment use which makes it essential that these items are tested regularly for safety. According to PAT testing legislation, a competent person is someone who has experience or knowledge of being able to check and test appliances for safety purposes. Those with knowledge of electricity in general as well as anyone who has experience in electrical work can be deemed capable. It is imperative that employers, landlords and self-employed individuals follow the rules to ensure that their workplaces are safe. Testing can be done by any number of PAT testing companies or individuals can obtain certification to perform their own testing by successfully completing coursework in this field. 

Frequency of PAT Testing 

In order to determine how often you should have your appliances tested, you should bear in mind a few different factors: 

  • Equipment that is used more should be tested more frequently. This equipment is likely to suffer less damage than that used regularly. 
  • If people using equipment report any damages as they become noticeable, there is less chance of a major hazard. If equipment regularly receives damage or abuse that is not reported then inspections and testing are required more frequently. 
  • The type of equipment in question is a major factor in determining PAT testing frequency. Hand held appliances are more likely to become damaged than those that are stationary. Class 1 appliances carry the greatest risk of danger and should be tested more often. 

Portable appliance testing is the visual examination and electrical testing of portable electrical equipment used in industrial, commercial or public access areas and locations (including rented property) to ensure they are safe to use, and cannot present an electrical hazard to the operator or anyone in their vicinity. Among the issues that can arise are: 

  • Exposure to live, conductive parts due to damage to the outer casing of the equipment.  
  • Worn and/or frayed power cord.  
  • Defective, lose or missing earth/ground connections.  
  • Failure to identify and correct problems such as those listed above can result in the electrical equipment becoming a shock hazard or a fire risk.  

Many of these problems can be identified visually, but still often go unreported. Internal faults often go undetected. Portable appliance testing involves performing a series of tests that, taken together, are designed to identify any faults or product defects that would otherwise not be detected. In addition to protecting personnel, regular safety checks of electrical equipment tend to increase the operational life of equipment. 

How PAT Testing is Done? 

Visual Examination 

Visual examination is vital and always precedes electrical testing. It often reveals major defects that would not be revealed by testing alone.  

Categories of in-service visual examination and electrical testing are divided into three types:  

1. Operator Checks (no records if equipment is OK).  

All users of equipment must understand how important operator checks are. Some equipment and environments may demand special needs but generally the following list is a typical checklist that operators should be using. 

  • Check the condition of the appliance/equipment (look for cracks or damage). 
  • Examine the cable supplying the item, looking for cuts, abrasions, cracks, etc. 
  • Check the cable sheath is secure in the plug and the appliance. 
  • Look for signs of overheating. 
  • Check that it has a valid label indicating that it has been formally inspected and tested and the date of the next inspection and/or test. 
  • Decide if the item is suitable for the environment in which it is to be used, for example 230 V appliances should not be used on a construction site, unless protected by a 30 mA RCD. 
  • If all these checks prove satisfactory, check that the appliance is working correctly. 
2. Formal Visual Examination (recorded) 
  • Check cable runs to ensure that cables will not be damaged by staff or heavy equipment. 
  • Make sure that plugs, sockets, flex outlets, isolators, etc. are always accessible to enable disconnection/isolation of the supply, either for functional, maintenance or emergency purposes. For example, in many office environments, socket outlets are very often obscured by filing cabinets. 
  • Check that items that require clear ventilation, such as convector heaters, VDUs, etc., are not covered in paper, files, etc., and that foreign bodies or moisture cannot accidentally enter such equipment. 
  • Ensure that cables exiting from plugs or equipment are not tightly bent. 
  • Check that multi-way adaptors/extension leads are not excessively used. 
  • Check that equipment is suitable for both the purpose to which it is being put and the environment in which it is being used. 
  • Ensure that accessories/equipment are disconnected from the supply during the inspection process, either by removing he plug or by switching off at a connection unit or isolator. 
  • Take great care before isolating or switching off business equipment. Ensure that a responsible person agrees that this may be done, otherwise this may result in a serious loss of information, working processes, etc. 
3. Combined Visual Examination and Electrical Testing (recorded): 

At periodic intervals, the portable appliances are tested to measure that the degree of protection to ensure that it is adequate. At these intervals, a formal visual inspection is carried out and then followed by PAT testing. Note the inside of the plug should be checked unless it is moulded or there is an unbroken seal covering the screws (bad internal wiring or an unsuitable fuse would cause the item to be classed as dangerous). 

Frequency of Visual Examination and Electrical Testing depends on a number of factors. No strict test schedules exist. If the cable passes your visual inspection, use a standard test lead (included with most PAT testers) to perform the following testing procedures: 

Earth Bond/Continuity Test  

Earth bond/continuity tests only apply to Class I equipment and are used to confirm the existence of a safety return path. The purpose of the test is to ensure that the ground terminal has a low resistance connection to the conductive metal casing of the appliance. An effective connection to the system ground within the fixed installation of the premises ensures safety. There are two methods available and different circumstances will require each method:  

Testing is performed using an ohmmeter or PAT tester; 

  • Using the ohmmeter to produce a reading 
  • Using a PAT tester under the following conditions 
  • 12V maximum, test current range 100mA to 200mA – commonly known as “earth continuity test” or “screen test” 
  • 12V maximum, test current 10A – commonly known as “routine test” 
  • 12V maximum, 1.5 times rated current of appliance or 25A, whichever is greater – commonly known as “type test” or “bond test”
Low Current Continuity Test:  

A continuity measurement should be made using a short circuit test current between 20-200 mA between exposed conductive parts of the equipment and the earth pin of the plug (or earth/ground-terminal of the supply). This test is performed using the earth bond lead. The maximum value of resistance should be noted while flexing the asset supply cable and a visual examination of the power cable terminations at both ends should be made. Any fluctuation in the reading should be investigated to identify the cause. The test current is so low that there is no risk of damaging earth connections that may exist for functional, rather than safety, reasons. This low-current test is sometimes referred to as a “soft test.”  

High Current Bond Test

A continuity measurement using a test current of max 26A for between 5 to 20 seconds. This test is used where the user has concerns that a ground may be maintained by a few strands of wire or where poor surface contact by the probes or clips could give a misleading reading. The bond test should be connected between exposed earthed/ grounded conductive parts of the equipment and the ground pin of the plug (or ground-terminal of the supply). This is done by connecting the earth bond lead to the exposed metalwork. The maximum value of resistance should be noted while flexing the asset supply cable and a visual examination of the power cable terminations at both ends should be made. Any fluctuation in the reading should be investigated to identify the cause. 

Insulation Test  

The insulation test is used to confirm that there is separation between the live conductors (live and neutral) and any accessible conductive parts. Generally, insulation testing is carried out by applying a known test voltage (500 V DC) and measuring the resistance. On sensitive equipment (IT for example) 500 V may cause damage, and so be unsuitable. Therefore, it may be substituted with a low-voltage (250 V) insulation test, a touch current test or an alternative leakage current test. Appliances must not be touched during an insulation test because, if a fault exists, the exposed metalwork may rise to the test voltage, although this voltage in itself is not dangerous. It is performed using an ohmmeter or portable appliance tester by applying a nominal voltage to the live conductors (active and neutral) of an appliance, and placing 0 volt reference on the earthed parts of a Class I appliance or the external metal parts of a Class II appliance.

The test method varies, depending on whether the appliance is Class I or Class II. For a grounded (Class I) appliance, the insulation test is carried out between the earth pin and the combined live and neutral pins of the plug. Megger PAT testers make 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 or dirty/conductive areas of the casing which may involve several tests. The connection method is the same as that used for the earth bond/continuity return, using the same lead. 

Differential Leakage Test  

The differential leakage current (also called protective conductor current) test measures the difference in current between the live and neutral conductors and determines if any current is flowing to earth. Normally, appliances should have no, or very little, earth leakage current. Class II (double insulated) appliances could exhibit earth leakage through their mountings or by operator contact. During the test, the actual mains voltage is measured at the appliance socket. To ensure that the equipment is safe even when the mains supply rises to its maximum permitted value, the PAT calculates and displays the leakage current that would flow at this value. 

Leakage Current Test  

It is performed at rated voltage with values not exceeding 5mA for Class I appliances or 1mA for Class II appliances. 

Alternatively, measure insulation resistance values are not less than 1MΩ for Class I and Class II appliances at 500 V d.c. or alternatively, to avoid the equipment apparently failing the test because the metal oxide varistors (MOVs), or electro-magnetic interference (EMI) suppression has triggered, for equipment containing voltage limiting devices such as MOVs, or EMI suppression, at 250 V dc. 

Leakage current testing is performed using a PAT by applying a nominal voltage to the live conductors (active and neutral) of an appliance, and placing 0 volt reference on the earthed parts of a Class I appliance or the external metal parts of a Class II appliance. 

Load Test  

The load test (also called the operational or VA test) measures the power consumption of the equipment when running. Measuring the load (VA) of an appliance is a good indication of its operating condition. By setting a load VA limit in the instrument’s test groups, an appliance can be assessed automatically for excessive load. The load VA limit is usually set based on the rating plate on the appliance. When using the Megger portable appliance testers, which power up the equipment for you, a functional test is carried out during the “load” test. This test will determine:  

  • If the asset functions correctly  
  • The VA rating of the appliance  

The results of this test 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. Care should be exercised when electrical… 

Polarity Check 

In countries where the sockets are polarised, polarity testing is a simple test that can be carried out using a polarity tester to determine whether the active and neutral of the plug end are correctly connected to the corresponding terminals at the socket end 

Note: The earth is tested during the earth continuity test. In the UK, as per BS7671, the phase (‘Live’ or ‘Hot’) cable should connect with right hand side terminal of the socket (if we face the socket outlet). 

Flash Testing  

Flash testing measures the leakage current when high test voltages are applied to an asset. The flash test provides a high ac test voltage (2500 V or 3000 V) and measures the leakage current. This test can be destructive and is usually only used on equipment that has been repaired. It is not generally used for “in-service testing” of electrical equipment. 

Labelling 

Any equipment that requires visual examination and electrical testing must be clearly labelled. The label must consist of a unique identifier for the equipment, the date it was tested, the re-test date and an indication of its state. A failed asset does not need the dates on, just clear identification that it has failed. Labels may either be filled in by hand or printed. Printed labels often consist of a bar code for the identifier making them easy to read with a suitable barcode scanner. This is a great time saver with an instrument that supports it such as the PAT400 Series by Megger. Labels should be manufactured so they can… 

Documentation  

The following records should be established and maintained:  

  • A register of all equipment  
  • A record of formal and combined visual examinations and electrical tests  
  • A register of all faulty equipment  
  • A repair register  

All of these records can be stored on paper or electronically, as long as reasonable precautions are taken with regard to the safeguarding of the data. Whichever method is chosen, previous test results must be available to the test operative. Our company maintains the following paper or electronic records Copy of the formal visual examination and combined visual examination and electrical test results and register of all equipment repaired. 

Report 

On completion of the testing you will be issued with a safety certificate and a detailed report that provides information on each individual item.  All items that pass the inspection & testing will be labelled with a safety sticker and a unique barcode number that helps us keep track of all portable appliances in your company.


Source: https://carelabz.com/what-pat-test-why-pat-test-done/

Published by PQTBlog

Electrical Engineer

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