PAT Procedures
Inspection and Testing of Portable Electrical Items
Commonly known as Portable Appliance Testing (PAT), involves visual checks and electrical tests to ensure equipment is safe to use. These procedures help prevent electric shock, fire, and equipment failure
PAT testing is not legally required for every appliance, but employers and landlords must ensure electrical equipment is safe under the Electricity at Work Regulations 1989
Some Tips for the Multiple Choice Questions…
This is an important section focused on testing knowledge ref to carrying out the inspection and testing:
- Identify tests that are suitable for the different types and classifications of in-service equipment (Page 69).
- Identify fake or inappropriate equipment (Page 90).
- Identify the range of test instruments that can be used for testing electrical equipment (Pages 63 to 66).
- Explain the need for test instruments and accessories to be accurate and in good working order (Page 66).
- Understand how to safely isolate a supply before working on equipment (Pages 60 to 61).
- Understand the difference between switching and isolation (Page 60).
- Calculate the resistance of the flexible cable conductors and protective conductors (Page 107).
- Know how to carry out protective conductor continuity testing (Pages 70 to 72).
- Know how to carry out insulation resistance testing (Pages 72 to 73).
- Understand the application of the protective conductor/touch current test (Pages 73 to 74).
- Know how to carry out polarity checks (Page 75).
- Know how to carry out functional checks (Page 74).
- Describe the requirement for testing RCDs (Pages 77 and 78).
- Know the requirements for testing equipment lead sets (Page 75).
- Understand requirements for equipment that has a high protective conductor current (Page 78).
- Interpret results that come from testing (Pages 71, 72 and 74).
- Specify the actions to be taken with damaged or faulty equipment (Page 87).
Legal and Regulatory considerations:
Electricity at Work Regulations 1989: Requires safe maintenance of electrical equipment
HSE Guidance: Emphasises visual checks and risk-based testing intervals
No fixed legal interval: Employers must assess risk and set appropriate schedule
This sections spans a few chapters of the Code of Practice, so you may need to refer to the following:
Chapter 7 – User Checks
Chapter 8 – Formal Visual Inspection
Chapter 10 – Electrical Tests
Chapter 11 – The Frequency of In-Service Inspection and Testing
Appendix 6 – User Checks and Formal Visual Inspection
Common Equipment Categories
Note: The frequency of testing depends on environment, usage, and risk assessment
Installation Resistance Readings
Insulation resistance readings for PAT testing must exceed specific thresholds to pass:
Typically, greater than 1 MΩ for Class I appliances and greater than 2 MΩ for Class II appliances
Testing Procedures
Conducted at 500 V DC for approximately 5 seconds using a PAT tester
The tester typically shorts the live and neutral pins together internally and measures resistance to earth
If the appliance contains surge protection or filters, the test may fail falsely – use an earth leakage test instead in such cases
Pass / fail Criteria:
A reading above the threshold indicates good insulation and a pass
A reading below the threshold suggests poor insulation and a fail – the appliance should be removed from service or repaired
Additional Notes
- Always perform an earth continuity test first for Class I appliances.
- Ensure the appliance is switched on during testing to allow full circuit evaluation.
- Record results and label the appliance accordingly.
Testing a Class I Appliance
A Class 1 appliance should have the power switch in the on position, if this is not possible pressing the test button a 2nd time would carry out the test. Plug the appliance into the tester and select the Class 1 test.
The insulation test pass mark will be 1MΩ. This means that the Insulation reading must be over 1MΩ to Pass the test. The PAT tester will measure the resistance between the live parts (Live and Neutral) connected together and earth.
Testing Class II Appliances
If you decide you need to test a Class II appliance with the insulation resistance test, then there’s a slightly different procedure to follow.
The appliance switch should still be in the ON position whilst carrying out the test.
The main different between the Class I and II test is that for Class II appliances you must connect a test probe (lead) to any metal point on the appliance in question. If you had a drill, you’d hold it onto the ‘chuck’ or screws within the bodywork. If someone had damaged the internal live parts or let’s say gone through the live cable within the appliance, then this test would pick up that the screw had gone through the live cable.
It is important for most appliances that you complete this test multiple times on all the different metal sections in order to assess that the correct level of insulation is present throughout the entire appliance.
For this test the insulation resistance should be greater than 2MΩ between the live + neutral and the metallic part of the appliance.
Testing Appliances and Extension Leads with Surge Protection
Surge protection devices are more commonly found on extension leads fitted to IT equipment.
It is common to use a standard voltage of 500V when the testing is carried out. Appliances that are surge protected are different because they have circuitry built into the appliance to prevent a “surge” of electricity from entering and damaging the appliance.
This circuit is designed to monitor the incoming voltage into the appliance and if it rises above 250 volts the circuit will “divert” the extra voltage away safely down the earth cable of the appliance.
When we carry out a PAT test at 500v d.c. the voltage used often triggers the surge protection circuit. For this reason, most appliance testers are fitted with a 250-volt insulation test option which will not trigger the surge protection device.
Not all PAT testers have this capability, so it is also acceptable to use a touch current test instead.