Portable Appliance Testing (commonly known as PAT or PAT Inspection or PAT Testing) is a process in the United Kingdom by which electrical appliances are routinely checked for safety. The correct term for the whole process is In-service Inspection & Testing of Electrical Equipment.
When people work with electrical appliances, health and safety regulations state that the appliance must be safe, to prevent harm to the workers. Many types of equipment require testing at regular intervals to ensure continual safety; the interval between tests depending on both the type of appliance and the environment it is used in. If a worker is injured by non-compliant equipment
Evidence of testing is 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 they use.
Portable appliance testing and inspection however was conducted on a 3 month (high risk) and 6 month (low risk) cycle from the early 1960s onwards in government departments under the control of the Department of the Environment Property and Services Agency (circa 1970 to 2000) as the DOEPSA was known and prior to that as the Ministry of Public Buildings and Works (MoPBW) until about 1970.
Extensive record keeping was made into log-books and generally equipment used was an insulation resistance tester simple hand tools and visual inspection 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 1990 that are frequently quoted as the reason that PAT inspection is done.
In reality neither act nor their corresponding regulations detail PAT inspection as an obligation but rather state a requirement of maintenance of safety and evidence of routine maintenance of all hand-held, portable and plug-in equipment.
It seemed inevitable with the increasing amounts of such equipment in domestic, commercial and industrial environments that the system employed for all government departments would become more formalized and adopted as a method for assuring safety of appliances in the world beyond the civil service departments.
Testing equipment specifically designed for PAT inspections was developed as mobile versions of the equipment used by manufacturers for testing their equipment at the end of the manufacturing process to ensure compliance with the relevant or corresponding BS (British Standard Code of Practice) for that type of appliance.
One other check carried out on high risk equipment such as hand held electrical mains drills class I equipment when issued from a government department stores was the Earth Test this test passed a current of 25amps down the earth conductor (the c.p.c. circuit protective conductor as it is currently named) to substantiate that the earth was a sound and valid connection for safe disconnection in the event of a fault occurring

 The Electricity at Work Regulations (1989) requires "All electrical systems shall be maintained so as to prevent, so far as is reasonably practicable, any danger". This is interpreted as covering the fixed electrical installation as well as portable and transportable equipment connected to it. The Regulations also state "It is the duty of every employer and self employed person to comply with the provision of these Regulations."
British law (the Electricity at Work Regulations 1989 in particular) requires that all electrical systems (including electrical appliances) are maintained (so far as is reasonably practicable) to prevent danger. Guidance from the Institution of Engineering and Technology (IET, published under the IEE brand) and the Health and Safety Executive (HSE) suggest initial intervals for combined inspection and testing that range from three months (for construction equipment) to five years for inspection and, in many cases, never for testing (certain types of appliance in schools, hotels, offices and shops).
Electrical systems refer to the installation as well as all the appliances connected to it. A qualified electrician would normally inspect the installation at periodic intervals. For an office, this is typically every 5 years and for say a hotel where the risk may be higher, it may need to be done annually. The maintenance of the appliances can largely be carried out in-house in many organizations. This can result in cost savings and more flexibility in when PAT testing is carried out.
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 the Trading Standards. However, it is important to have a maintenance regime for electrical appliances. The Electricity at Work Regulations (1989) requires that electrical appliances be maintained so that they remain safe during use. The implementation of this is up to employers. The HSE or the local authority is responsible for the policing of this.