Plus: everything you need to know about PAT inspection equipment
The yearly PAT inspection is part and parcel of your company’s responsibility of creating a safe workplace. As well as being a two-way thing between employers and employees, health and safety also apply to the safety of your tools. That of machinery, computer systems or vacuum cleaners for example.
Health and Safety regulations state that electrical appliances should be safe with continuous building maintenance procedures. This is to prevent harm to workers. Before 1989, PAT inspection was covered by the Health and Safety at Work Act 1974. In 1989, another act was created: the Electricity at Work Regulations. This ensures that public and private sector enterprises have their appliances checked on an annual basis.
Prior to then, appliances were tested on government premises, with high-risk equipment, and on electrical installations. Records were kept in logbooks, testing was undertaken with simple hand tools and a resistance tester. This predated the 1974 and 1989 Acts with low-risk appliances being tested every six months. For high-risk appliances, that was every three months.
Types of PAT inspection tests
For a PAT inspection, there are four tests which form the core of each assessment:
- Earth resistance tests;
- Earth continuity tests;
- Insulation resistance tests;
- Polarity checks.
Earth resistance tests gauge the resistance of any appliance with earthing rods. The resistance of each device should be no more than 1Ω.
Earth continuity tests measure the resistance of the protective earth circuit or the earthing conductor of an extension cord or appliance cord. Again this should be no more than 1Ω. A PAT inspection test is conducted with an ohmmeter or PAT tester.
An insulation resistance test is used to detect leakage current, not exceeding 5mA on Class I appliances (electrical appliances that require an earth wire), and 1mA on Class II appliances (where an earth wire isn’t needed).
With a polarity tester, polarity checks are made to assess the active and neutral wires. This is used to see if both wires are properly connected.
Types of PAT inspection testers
Depending on the complexity of the task, there are three principal types of Portable Appliance Testing devices.
This is the most basic form of PAT inspection devices. A simple ‘pass’ or ‘fail’ result is given by one of its two lights. They include settings for Class I appliances (with metal/plastic options) and another for Class II appliances. They can measure earth continuity, insulation resistance and polarity levels.
Advanced PAT testers
A more advanced system uses predetermined parameters, with a typical range of 0 – 1.99Ω at high test currents for earth continuity resistance (8A, 10A and 25A), and lower test currents (20mA – 200mA). Insulation resistance functions often have test voltages of 500V DC and 250V DC. They also have fuse and lead polarity testing functions.
Computer-based PAT tester
A computer-based portable appliance testing system records the results digitally. Information can be downloaded onto a computer. These allow for two-way communication between tester and PC, often via Bluetooth.
ST Maintenance, 04 August 2016.