Common Mistakes to Avoid During PAT Testing

PAT testing is a structured inspection and testing process designed to identify defects that could lead to electric shock, fire, or equipment failure. It involves far more than simply connecting an appliance to a tester and pressing a button.

Accurate results depend on using the correct inspection method and test setup for the equipment type. A disconnected lead, an appliance left switched off, or a plug that hasn’t been opened can all produce misleading “pass” results.

This article highlights some common errors made during PAT testing and explains how to avoid them.

Key takeaways

Not Connecting the Test Lead

During an insulation test on Class II equipment, the test lead must be connected to any accessible metalwork (or other conductive parts that could become live). This is commonly missed, and the test will almost always “pass” if the lead is left disconnected.

For Class II equipment, the insulation test measures resistance between accessible conductive parts and the live conductors. The test lead provides the return path back to the PAT tester. If it isn’t connected, the circuit is open and the tester reads an artificially high (often “infinite”) resistance, even if a fault exists. For Class I equipment, the protective conductor in the supply lead provides the return path, so a separate lead connection is not required for the insulation measurement.

Not Switching on the Appliance

When carrying out insulation and leakage tests, the appliance must be switched on so the test voltage reaches internal components. If the switch is off, anything downstream of the switch may not be tested.

For example, a kettle left “off” may allow a heating element fault to be missed. Some appliances have momentary or thermostatic switches that need to be held in the ON position during the test. Incomplete circuits can also lead to misleading results. See our article on “no load” warnings for further explanation.

Not Opening the Plug

The visual inspection is the most important part of the PAT process, and most faults are identified at this stage. Where a rewirable plug is fitted, it should be opened as part of the inspection. The wiring, tightness of terminals, condition of the cord grip, correct fuse rating, signs of overheating, and any physical damage should all be checked.

Moulded (non-rewirable) plugs must also be inspected carefully. Although they cannot be opened, the fuse rating should still be checked, along with the condition of the casing, pins, flex entry and any signs of overheating or damage. Incorrect fuse ratings are frequently found even in moulded plugs.

Inspectors should also remain alert for signs of non-compliance, such as poor-quality markings, missing rating information, incorrect pin configuration, or other features that may indicate counterfeit or substandard construction. See our examples of counterfeit and dangerous electrical equipment.

Assuming a 12-Month Retest Date

There is a persistent myth that all electrical equipment needs to be PAT tested every 12 months. This is not the case and never has been; the frequency of the inspection and testing should be based on risk assessment. Some equipment in high-risk environments may need more frequent testing and conversely, low-risk equipment does not usually require annual testing. We also have an article on how to set PAT inspection and test frequencies.

Not Recording the Test Measurement

Another common mistake is to record only a 'Pass' or 'Fail' result on the test records without documenting the actual test measurement. Recording measured values helps demonstrate the test was carried out correctly and also provides a useful tool for identifying potential issues. For example, if an earth continuity reading gradually increases with each subsequent test, it could indicate that the earth connection is corroding.

These mistakes are easy to make if PAT testing is treated as a “tick box” exercise. Good training helps testers understand what each test is actually proving, when results can be misleading, and how to carry out a proper visual inspection.

If you’re responsible for PAT testing in the workplace, see our Managing PAT Testing guide, or view our PAT testing courses for practical training and supervised testing practice.