Portable appliance testing

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 (redundantly) as "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 formal term for the process is "in-service inspection & testing of electrical equipment". Testing involves a visual inspection of the equipment and any flexible cables for good condition, and also where required, verification of grounding (earthing) 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.

Similar procedures exist in other countries, for example, testing of equipment according to DGUV Vorschrift 3 in Germany.

Purpose

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. 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.

Origin of Name

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

Appliances 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.

Fixed wiring in buildings 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 is often not required.[2] In 2011, the HSE reviewed its approach to portable appliance maintenance in its own offices. Thinking about the type of equipment in use, and how it was used, the HSE looked back at the results from its annual testing of portable appliances across its estate over the last five years. Using the results of the previous tests, the HSE decided that further portable appliance tests are not needed within the foreseeable future or at all for certain types of portable equipment. Also, they decided to continue to monitor any faults reported as a result of user checks and visual inspections and review its maintenance system if evidence suggests that it needs revising. Electrical equipment will continue to be maintained by a series of user checks and visual inspections by staff that have had some training.

Key Points:

Annual portable appliance testing is not always necessary in low risk environments. You do not need to be qualified as an electrician to carry out visual inspections. Regular user checks and visual inspections can be a good method of maintaining portable electric equipment.

Origins in UK

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. 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 early testing and inspection was done under a planned maintenance scheme and pre-dated both the Health and Safety at Work Act 1974 and the Electricity at Work Act 1989.

Site and campus requirements, events and contractors

In the UK there is no legal instrument that requires a sub-contractor to ensure that all tools and equipment are 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

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

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

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.[3]

Combined inspections and PAT testing

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

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

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

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.[4]

Testing is performed using an ohmmeter or PAT tester;

The choice of which of the tests 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 which may be in excess of 2000 watts.

Insulation resistance test

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

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.[6]

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;

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;

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

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.[7] 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

Cord extension sockets

RCDs /ELCBs / Safety Switches

There are two tests methods to be used;

Press Button

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

This test requires specialised test equipment, knowledge and training;

In addition to this, many technicians also test;

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

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

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

PAT testing at a workbench

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 where required, 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)'.[11] although there are others provided by EAL available.

In Australia it is a legal requirement to have attended a course or gained a qualification in order to PAT. Proof of a company’s competence takes 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

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. Many 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 can give much more information and testing features but are mainly aimed at more highly skilled users.

Pass / fail PAT testers

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:

Advanced PAT testers

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

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

RCD testing

Some units can also 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

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

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:

Dual purpose check boxes (which are essentially known resistances either side of the test limits)have also been introduced which are capable of validating the accuracy of both electrical installation testers and portable appliance testers in the field, reducing the risk of a tester being used when not operating correctly - this also allows the re-calibration interval to be increased.

See also

References

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

External links

This article is issued from Wikipedia - version of the Wednesday, March 23, 2016. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.