Portable appliance testing

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For other uses, see PAT (disambiguation).
A common label for certifying that a device has been tested.

Portable appliance testing (commonly known as "PAT", "PAT Inspection" or "PAT Testing") is the name of a process in the United Kingdom, the Republic of Ireland, New Zealand and Australia by which electrical appliances are routinely checked for safety. The correct term for the whole process is "in-service inspection & testing of electrical equipment".

Similar procedures exist in other countries, for example, testing of equipment according to BGV A3 in Germany.

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. The European Low Voltage Directive governs the manufacture or importation of electrical appliances. Compliance to this has to be declared and indicated by the display of the CE mark on the product. The responsibility for this lies with the manufacturer or the importer and is policed by Trading Standards.

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.

Name[edit]

Portable appliance testing is abbreviated as PAT. The correct term for the whole process is "In-service Inspection & Testing of Electrical Equipment" (as defined by IET/IEE and City and Guilds). In Australia, the common name for PAT is simply 'Test and Tag'. The regulatory guidelines are set out in AS3760:2013.

UK legal obligations[edit]

British law (the Electricity at Work Regulations 1989) requires that all electrical systems (including electrical appliances) are maintained (so far as is reasonably practicable) to prevent danger. Private houses are not covered by this legislation, although occupiers' liability requires householders not to deliberately expose occupants or visitors to unreasonable risks. The HSE and the local authority are responsible for the policing of this legislation.

Guidance from the Institution of Engineering and Technology (IET, published under the IEE brand) and the Health and Safety Executive (HSE) recommends that a competent person must inspect the installation regularly in any public building or a place that people work. They suggest initial intervals for combined inspection and testing that range from three months (for construction equipment) to one year, and in many cases, longer periods for re-testing (certain types of appliance in schools, hotels, offices and shops).[1]

Although the Electricity at Work Regulations 1989 is an obligation on UK businesses, there is no obligation to undertake PAT inspection. In reality neither act nor their corresponding regulations and associated statutory instruments detail PAT inspection as an obligation, but rather impose a requirement of maintenance of safety and evidence of routine maintenance for all hand-held, portable and plug-in equipment.

Today a great many private companies and other organizations do meet their legal obligations to protect their workers by an enforced PAT regime, but it is not the only route.

Recent HSE publications have relaxed their tone somewhat to acknowledge this, and now point out that in many situations annual PAT is disproportionate to the risks and not required.[2]

Electricity at Work Regulations 1989

The earliest formal portable appliance testing and inspection of both electrical installations and high risk equipment was introduced in the UK in government estates. This was under the control of the Property Services Agency – prior to 1972 the Ministry of Public Building and Works.[citation needed] In some cases testing was conducted on a three month (high risk) and six month (low risk) cycle from the early 1960s onwards. Extensive record keeping was made into log-books and generally the equipment used was an insulation resistance tester, simple hand tools and visual inspection. Evidence of testing was clearly visible to workers in the form of "passed", "tested for electrical safety" and "do not use after..." labels affixed to various parts of the electrical equipment used.

This testing and inspection was done under a planned maintenance scheme and predated both the Health and Safety at Work Act 1974 and the Electricity at Work Act 1989 that are frequently mis-quoted as the reason that PAT inspection is done.[citation needed]

Site and campus requirements, events and contractors[edit]

In the UK there is no legal instrument that requires a sub-contractor to ensure that all tools and equipment is PAT inspected before bringing onto a site of work. Neither is there any legal instrument which obliges the site owner to ensure third party equipment is PAT inspected either by themselves or the equipment owner.

The internal policies of many UK businesses and educational establishments make mistaken reference to PAT inspection being a legal requirement under the Electricity at Work Regulations, which is false. Having such a policy is legitimate for internal reasons, but it is not underwritten by law, it is only their interpretation. Therefore it is not a legal requirement to have a PAT inspection sticker or certificate, the obligation is that equipment must be safe.

The HSE recommend policies use phrases such as "Equipment that is brought onto site for an event must be in a safe condition" and refrain from overzealous statements such as "must be PAT inspected" which can be restrictive without improving safety. Overall it is safer if a competent person makes a visual inspection than if a layman merely observes the presence of a sticker.

Carrying out PAT testing[edit]

This can be done by hiring an external company to test all the electrical products in a business (someone who has had some PAT training, either by an official qualification or by attending a health and safety course offered by some electrical health and safety companies) 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.

User checks[edit]

Advising the user of potential danger signs can result in problems being picked up before they can result in any danger. For example, if the power cable is frayed or the plug is cracked, users need to be advised not to use the appliance and report the fault to a supervisor. This information can be put across, say by the use of a poster or in a memo. User checks are always carried out before operation, and the results are generally not recorded, unless a defect is identified.

Formal visual inspections[edit]

This is a process of simply inspecting the appliance, the cable and the plug for any obvious signs of damage. According to the HSE, this process can find more than 90% of faults.

Combined inspections and PAT testing[edit]

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).

Testing[edit]

The tests an appliance is required to undergo will depend on the type of appliance, its electrical Class and subject to a risk assessment by the technician. e.g. it may not be safe to perform a leakage current test which powers up the appliance, such as a grinder, if it can not be secured to a bench; an insulation resistance test may be a safe option.

Earth resistance test[edit]

This test shows the resistance offered by the earthing rods with the connection leads. Various testing instruments are available for earthing resistance tests. The earthing resistance should be less than 1Ω.

Earth continuity test[edit]

The equipment shall have a measured resistance of the protective earth circuit, or the earthing conductor of an extension cord or appliance cord set, which does not exceed 1Ω.[3]

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" and/or
    • 12V maximum, 1.5 times rated current of appliance or 25A, which ever is greater - commonly known as "type test" or "bond test".

The choice of which test(s) to use is at the operator's discretion as there is merit in each test for given situations. Later model testers that are battery powered are limited to doing the "screen test". Older mains powered units can do all tests. Even "type testing" may only be testing at a fraction of the operational power of the unit.The power dissipated in the earth is only 300 watts compared to operational power may be in excess of 2000 watts.

Insulation resistance test[edit]

A leakage current test performed at rated voltage with values not exceeding 5mA for Class I appliances or 1mA for Class II appliances.[4]

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 d.c.[5]

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;

  • Nominal voltage is 230V AC. (therefore it can not be performed with a digital multimeter)

Insulation Resistance testing 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;

  • Nominal voltage is 500V d.c (250 V d.c. may be used for equipment containing MOVs / EMI filtering)

A deficiency of the Insulation Resistance (500V/250V d.c) test is that the d.c voltage will not activate electromagnetic switches or internal relays etc. that are common in many modern power tools, computers, TVs etc. and therefore it can only test the appliance up to that point. Appliances with these components / design should be tested using the leakage current test.

Polarity check[edit]

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.[6] 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).

Plugs[edit]

  • The order (polarity) of the pins of a three pin flat pin plug, to their connections, shall be Earth (radial pin – green/yellow wire), Neutral (light blue wire) and then Active (brown wire), in a clockwise direction, when viewed from the front of the plug looking at the pins.[7]

Cord extension sockets[edit]

  • The order (polarity) of the socket apertures of a three pin flat pin socket, to their connections, shall be Earth (radial pin – green/yellow wire), Active (brown wire) and then Neutral (light blue wire), in a clockwise direction, when viewed from the front of the socket looking at the apertures.[8]

RCDs /ELCBs / Safety Switches[edit]

There are two tests methods to be used;

Press Button[edit]

This test requires specific test equipment RCD tester:

The RCD tester should be connected with the socket, with earth terminal (must !!) and 1)select the testing range 'delta' (10mA,30mA,100mA,300mA,500mA). 2)Select half delta range, and press TEST button - the RCD should not operate, this ensures against nuisance tripping. 3)Select delta range, and press TEST button - The RCD should operate, within m Sec for 50 Hz,230V system (as per BS 7671)

Applied current[edit]

This test requires specialised test equipment, knowledge and training;

  • A current, equal to the rated tripping current, shall be “suddenly” applied between active and protective earth and the operating time measured[9] with maximum trip time 40ms for Type I and 300ms for Type II.

In addition to this, many technicians also test;

  • using 1/2 (half) the rated tripping current to detect nuisance tripping.
  • using 5 times rated tripping current, with trip times reduced accordingly, to simulate high current exposure.
  • under 0 degree and 180 degree phases

Best Practice is to test the RCD under 1/2, 1X and 5X rated tripping current, each at both the 0 degree and 180 degree phases.

Class of construction[edit]

Electrical appliance classes are differentiated by a series of IEC protection classes. The protocols for PAT Testing vary by appliance class.

  • Class I – Single insulated wiring, which requires an earth connection. There is no symbol for a Class I product so if a rating plate has no symbol on it then it is usually Class I.
  • Class II – Double insulated wiring, The earth clamp is still connected during the insulation test even though no earth on appliance. Class II is indicated by double box.
  • Class III – These are appliances that are supplied at a low voltage (usually called Separated Extra Low Voltage) which must be less than 50 V. These appliances are supplied with a transformer supply that is also marked.

The earth lead is connected to metal parts on both Class I and Class II appliances. For "Class I" during the earth test to prove continuity between earth pin and metal parts on the appliance. For "Class II" during the insulation test to prove the insulation between active-neutral and the metal parts of the appliance. i.e. there is no leakage from mains coming into the appliance to the metal parts that are exposed.

PAT training and qualifications[edit]

PAT testing at a workbench

It is not stated in the health and safety regulations for an individual to have any qualifications to PAT Test but it does state that it must be done by a competent person who has been given instruction to perform the necessary checks in a safe manner. Personnel performing PAT may attend a course for training.

In the UK, there is no requirement to have a formal qualification for persons carrying out PAT Testing. The Electricity at Work regulations of 1989 simply state that inspecting and testing must be carried out by a competent person, however does not mention a benchmark for competency. It has become accepted practice, however, for individuals operating as PAT Testers to hold a 2377–22 City and Guilds qualification. PAT Testers in the UK do not need to be electricians or have a background in the electrical industry. An example of a nationally recognised qualification of competence in PAT is offered by City & Guilds: 'Code of Practice for In-service Inspection and Testing of Electrical Equipment – 4th Edition (No. 2377)'.[10] although there are others provided by EAL available.

It is a legal requirement to have attended a course or gained a qualification in order to PAT test in Australia. Proof of a company’s competence in PAT testing is usually found in the form of a course certificate or qualification. A formal examination process for the topic is operated in collaboration with EAL or city and guilds (the awarding body) under the authority of the QCA (The Qualifications and Curriculum Authority) who validate and authorise the qualification.

Types of PAT testers[edit]

At the basic level PAT test instruments carry out basic safety checks. Most are equipped with an earth continuity test, insulation resistance test and the ability to check the wiring of detachable mains cords. They do not however include tests which involve applying mains power to the appliance under test, for example, a protective conductor current or touch current tests. The main kind for businesses are simple PASS/FAIL testers that are easy to use, and are aimed at in-house PAT testing with minimal interpretation of results. Advanced PAT testers give much more information and testing features but are mainly aimed at trained persons qualified to City & Guilds 2377 or EAL.

Pass / fail PAT testers[edit]

These are the simple-to-use and comparatively much cheaper portable appliance testers for most businesses who will test in-house to carry out the testing and suitable for a wide range of businesses. They simply say PASS or FAIL when a test is carried out. Mains powered testers require AC power. Battery operated PAT testers are self-contained and convenient to use. They usually come with rechargeable batteries.

These testers have a simple "lights" system. They have a "Pass" light, a "Fail" light, options for Class I metal / plastic or Class II. They also will show:

  • earth continuity
  • insulation resistance
  • polarity.

Advanced PAT testers[edit]

These testers display more information than just pass or fail, including:

  • Earth continuity resistance (aka Earth Bond) tests with a measurement range of 0 – 1.99 Ω at high test currents (usually 8 A, 10 A or 25 A) and lower test currents (in the range 20 mA to 200 mA), enabling a complete range of appliances including personal computers to be tested;
  • Insulation resistance tests at test voltages of 500 V DC or 250 V DC.
  • Protective conductor/touch current measurement (sometimes referred to as "earth leakage tests" on some older PAT units);
  • Fuse test;
  • Lead polarity.

These readings require interpretation by an electrician or someone with electrical qualifications. Advanced PAT testers are effective as facilities management tools because of they can record the location and test status of electrical equipment and appliances.

RCD testing

Some units can test Residual-current devices, following the recommendation in the current IEE Code of Practice to test any RCD fitted on an extension lead or multiway adapter.

Modern PAT testers include an RCD test

Computerised PAT testers[edit]

Some advanced PAT testers can download information to a computer. Bluetooth enabled computerised PAT testers make the two way transfer of test data between the tester and PC-based record keeping systems much simpler, and can be used with other test accessories such as label printers.

Calibration of PAT testers[edit]

As PAT testers are sophisticated instruments, it is important to make sure that they are continuing to measure correctly. If a company fails to check and maintain calibration, it could face difficulty substantiating any measurements in the event of a claim. It is usually recommended that calibration is carried out annually on a PAT testing unit.

When a PAT Tester is calibrated it is re-configuring it to match the original specification. This includes:

  • Calibrating the unit back to national standards. This is best performed by the product manufacturer (if they offer a calibration service) or a laboratory accredited by UKAS [11]
  • If it is mains powered, then a safety test must be carried out.
  • A calibration certificate should be issued to prove the PAT unit has been electrically tested.

Dual purpose checkboxes have also been introduced which are capable of validating the accuracy of both electrical installation testers and portable appliance testers.

References[edit]

  1. ^ Health and Safety Executive, Electrical safety and you
  2. ^ Maintaining portable electric equipment in low-risk environment
  3. ^ Standard: AS/NZS 3760:2003 “In-service inspection and testing of electrical equipment Sec 2.3.3.1
  4. ^ Standard: AS/NZS 3760:2003 “In-service inspection and testing of electrical equipment Sec 2. 3.3.2(a)
  5. ^ Standard: AS/NZS 3760:2003 “In-service inspection and testing of electrical equipment Sec 2.3.3.2(b). General
  6. ^ BS7671 wiring rules OR Best Practices in Testing & Tagging of Electrical Equipment to AS/NZS 3760:2003. (Zahra & Virieux 2007) 5.8.1
  7. ^ Standard: AS/NZS 3760:2003 “In-service inspection and testing of electrical equipment Sec 2.3.3.5(a). General
  8. ^ Standard: AS/NZS 3760:2003 “In-service inspection and testing of electrical equipment Sec 2.3.3.5(b). General
  9. ^ Standard: AS/NZS 3760:2003 “In-service inspection and testing of electrical equipment AppendixD D3
  10. ^ City & Guilds 'Code of Practice for In-service Inspection and Testing of Electrical Equipment' qualification
  11. ^ The United Kingdom Accreditation Service

External links[edit]