In electrical safety testing, portable appliance testing (PAT inspection or PAT testing) is a process by which electrical appliances are routinely checked for safety, commonly used in the United Kingdom, Ireland, New Zealand and Australia. In Australia and New Zealand it is commonly known as Test and Tag. The formal term for the process is In-service Inspection & Testing of Electrical Equipment.
Testing involves a visual inspection of the equipment and verification that power cables are in good condition. Additionally, other tests may be done when required, such as a verification of earthing (grounding) continuity, a test of the soundness of insulation between the current-carrying parts, and a check for any exposed live metal that could be touched. The formal limits for a pass/fail of these electrical tests vary somewhat depending on the category of equipment being tested.
Other countries have similar procedures, for example, testing of equipment according to DGUV Vorschrift 3 in Germany.
Purpose Health and safety regulations require that electrical appliances are safe and well maintained to prevent harm to workers. Many equipment manufacturers recommend testing at regular intervals to ensure continual safety, with the interval between tests varying based 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 with these standards has to be declared and indicated by the display of the CE mark on the product. The responsibility for testing lies with the manufacturer or the importer and is policed by Trading Standards.
In Australia and New Zealand the standard used is AS/NZS3760.
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.
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 it is reasonable and practicable) to prevent risk of injury or danger. Domestic premises 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 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).Health and Safety Executive, Electrical safety and you
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 an annual PAT test is disproportionate to the risks and is often not required.Maintaining portable electric equipment in low-risk environment 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.
Annual portable appliance testing is not always necessary in low risk environments. In practice, decisions about when to test often take into account how equipment is used on a daily basis and the conditions it operates in. 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. For landlords maintaining legal requirements it is not compulsory for them to have all appliances tested, but they do need to show a "duty of care" and most letting agents recommend that a test certificate is obtained.
Worksite 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, rather 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.
Origins in UK
The first official appliance-testing equipment in the UK was used for government housing 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 etc. Act 1974 and the Electricity at Work Regulations 1989.
Inspection PAT testing is not exclusively confined to formal testing but is rather a combination of inspection and testing processes. Most dangerous defects can be found simply by inspecting the appliances for obvious signs of damage such as frayed cables. According to the HSE, simple inspection can find more than 90% of defects.
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. For example, it may not be safe to perform a leakage current test which powers up the appliance, if that appliance is something like a grinder, if it cannot be suitably secured.
The test equipment earth lead/probe is connected/touched to metal parts on both Class I and Class II appliances. For Class I an earth test is performed to prove good continuity between the earth pin of the appliance's plug and exposed metal parts on the appliance. For Class II an insulation test is performed which checks that voltage injected on the supply wires ( and neutral) is sufficiently insulated from the appliance's case and any exposed metal parts (e.g. connectors).
Earthing continuity/resistance 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.Standard: AS/NZS 3760:2003 In-service inspection and testing of electrical equipment Sec 2.3.3.1
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".
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. The purpose of the high current test is to simulate a fault condition: if a live part contacts the earthed metalwork, the earth conductor should be able to carry sufficient current to blow the fuse and render the appliance safe, without the earth conductor itself burning out. On the other hand, some equipment (especially IT equipment) could be damaged by this test, as the earth connection is only for functional purposes and is not meant to be relied upon for safety.
Insulation resistance test An insulation resistance test is performed to check the condition of conductor and component insulation. Values should not be less than 1MΩ for Class I and 2MΩ for Class II appliances at 500 V d.c., or at 250 V d.c.Standard: AS/NZS 3760:2003 In-service inspection and testing of electrical equipment Sec 2.3.3.2(b). General to avoid the equipment apparently failing the test because the metal oxide varistors (MOVs) or electro-magnetic interference (EMI) suppression triggered, for equipment containing voltage limiting devices such as MOVs or EMI suppression.
This test is performed using an insulation resistance test meter, or PAT tester, by applying a nominal voltage to the live conductors ( 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;
Leakage current test A leakage current test is sometimes used as an alternative to the insulation resistance test. A deficiency of the insulation resistance test is that the DC voltage will not activate electromagnetic switches or internal relays etc. that are common in many modern power tools, computers, and TVs, etc. and therefore it can only test the appliance up to those components. For such appliances an alternate leakage current test is available on some testing equipment which performs an AC based test (at reduced voltage), with values not exceeding 5mA for Class I appliances or 1mA for Class II appliances.Standard: AS/NZS 3760:2003 In-service inspection and testing of electrical equipment Sec 2. 3.3.2(a)