Electrical

PAT Testing: A Complete Guide

"PAT testing" is the everyday name for the in-service inspection and testing of electrical equipment — a mix of looking, testing and record-keeping that keeps portable appliances safe in use.

Updated 24 Aug 20268 min read

Portable Appliance Testing, or PAT, is the phrase everyone uses, but it undersells the job. The correct term in the IET Code of Practice is the in-service inspection and testing of electrical equipment, and the emphasis on inspection is deliberate: the majority of faults are found by looking, not by plugging into a tester.

This guide sets out what in-service inspection and testing actually involves, the difference between user checks, formal visual inspections and combined inspection and test, how Class I and Class II equipment are treated differently, the core tests, and why there is no legally fixed retest frequency.

Key takeaways

The correct term is in-service inspection and testing of electrical equipment — "PAT" is just shorthand.
Most defects are found by visual inspection, not by the tester — never skip the look.
Class I relies on an earth connection; Class II relies on double or reinforced insulation, so they are tested differently.
The two core electrical tests are earth continuity (Class I) and insulation resistance.
There is NO legally mandated retest interval — frequency is risk-based, guided by the IET Code of Practice.

What in-service inspection and testing actually is

The Electricity at Work Regulations 1989 require electrical equipment to be maintained so as to prevent danger, but they don’t say how. The IET Code of Practice for the In-Service Inspection and Testing of Electrical Equipment fills that gap with a recognised method. Duty holders use it to demonstrate that equipment has been maintained.

The regime has three tiers. User checks are informal looks carried out by the person using the equipment — checking for damaged flexes, cracked plugs or scorch marks before use. Formal visual inspections are a documented look by a competent person. Combined inspection and test adds the instrument tests on top of a formal visual inspection. The visual element is doing most of the work: a large share of dangerous defects are visible without ever touching a tester.

The word "portable" is misleading

The regime covers far more than portable appliances — it includes movable, hand-held, stationary, fixed and IT equipment. Anything with a plug, and some hard-wired items, can fall within scope.

Class I versus Class II

How an appliance protects the user against electric shock determines how you test it. Class I equipment relies on basic insulation plus a connection to the protective earth: if a live part touches the metal casing, the earth carries the fault current away and the protective device disconnects. A kettle, a toaster or a metal-cased power tool is typically Class I.

Class II equipment (double insulated, marked with the square-in-a-square symbol) has no reliance on an earth connection. Protection comes from two layers of insulation, or reinforced insulation, so there is no exposed metal that can become live. Most modern plastic-cased chargers, hair dryers and drills are Class II. Because there is no protective earth to check, a Class II item is not given an earth continuity test — you rely on the insulation resistance test and, crucially, the visual inspection.

The core electrical tests

Earth continuity applies to Class I equipment only. The tester passes a current between the earth pin of the plug and the accessible metalwork of the appliance and measures the resistance of that path. A low, stable reading confirms the earth connection is sound; a high or fluctuating reading points to a broken earth conductor or a poor termination — a serious fault, because it means a Class I appliance could become live without disconnecting.

Insulation resistance checks the quality of the insulation between the live conductors and earth (or, for Class II, accessible surfaces). A test voltage — commonly 500 V DC — is applied and the resistance measured; a healthy result is a high value in megohms. A low reading warns that insulation is breaking down and current could leak to earth or to touchable parts. Some equipment, such as items with surge protection or electronic components, needs an alternative approach so the test doesn’t damage it or give a misleading low reading.

Look before you test

Open the plug (where it isn’t moulded) and check the fuse rating, cord grip and terminations. A correctly wired but visibly damaged appliance still fails. The tester confirms what the eye can’t see — it doesn’t replace the inspection.

Frequency, labelling and records

There is no law that sets a fixed retest interval — not annually, not any other figure. The requirement is to maintain equipment to prevent danger, and the sensible way to decide how often to inspect and test is a risk assessment informed by the IET Code of Practice. A power tool on a busy site in a wet, knocked-about environment warrants far more frequent attention than a desk lamp in a quiet office that rarely moves.

Once an item has been inspected and tested, it is usually labelled with the date, the outcome and often the next-check date, so users and the duty holder can see its status at a glance. Records should identify each item, log the inspection and test results, and note any remedial action. It is the records and the risk-based schedule together — not a sticker alone — that demonstrate equipment is being properly maintained.

Frequently asked questions

Is PAT testing a legal requirement?

There is no law that names "PAT testing" or sets a frequency. The Electricity at Work Regulations 1989 require equipment to be maintained to prevent danger; in-service inspection and testing to the IET Code of Practice is the recognised way to show you have done so.

How often should equipment be tested?

As often as the risk demands. Frequency comes from a risk assessment guided by the IET Code of Practice, based on the equipment type, environment and how hard it is used — not from a fixed annual rule.

Do Class II appliances need an earth continuity test?

No. Class II (double-insulated) equipment has no protective earth to check, so earth continuity does not apply. You rely on a thorough visual inspection and the insulation resistance test.

From guidance to action

PAT testing certificateLog each item, record inspection and test results and issue the report on site.