PAT

Portable appliance testing is the systematic inspection and electrical testing of movable equipment used in workplaces, typically those connected by flexible cable and a plug. The goal is to verify that an appliance is safe to use and poses no risk of electric shock, fire, or burn hazard. PAT covers everything from desktop computers and kettles to power tools and laboratory instruments, and is mandatory in most industrial and commercial settings in the UK and several other jurisdictions.

A PAT typically consists of two stages: a visual inspection for obvious defects (damaged cable, loose plugs, burn marks, water damage), followed by electrical testing with a dedicated PAT tester. The tester performs insulation resistance testing, earth continuity testing, and a leakage current test. Insulation resistance is measured between live and earth conductors, usually at 500 V DC. Earth continuity verifies that the earth pin makes proper contact with the appliance frame. Leakage current is measured to confirm that current escaping through the insulation is within safe limits, typically below 3.5 mA for Class I equipment and 5 mA for Class II equipment.

Testing frequency depends on the equipment type and environment. Portable power tools used on construction sites may require testing every 3 months; office equipment every 2 years; kitchen appliances every 6 months. High-risk or high-use items are tested more frequently than those in low-risk environments. Records of all tests, including pass or fail results and the date of the next test, must be retained, usually on a label affixed to the appliance or in a database.

Why PAT matters in practice

Failures detected during PAT reveal insulation breakdown from moisture ingress, mechanical damage to cables, deterioration of plug pins, or loose earth connections. These defects may not cause immediate failure but represent cumulative risk. A damaged cable or corroded earth connection can lead to electrocution if an appliance develops a live fault. PAT is fundamentally a control on that residual risk, not a guarantee of safety under all conditions.

PAT testing is often performed by dedicated technicians using a calibrated tester, though some organizations train in-house staff. The equipment cost is modest (handheld testers range from a few hundred to several thousand pounds), making the test economically practical at scale. Regulatory bodies such as the Health and Safety Executive in the UK do not specify exact testing intervals, only that equipment be maintained in a safe condition; however, industry guidance and insurers typically enforce the intervals mentioned above. The discipline has become standard practice partly because the cost of testing is far lower than the cost of injury, downtime, or liability from electrical accidents.