PAT Testing Tests: What They Are and How They Work

If you've booked a PAT test for your office, shop, or rental property, you might assume it's a single quick check with a beeping machine. It's not. PAT testing tests actually cover a sequence of checks, from a visual inspection right through to electrical measurements that verify an appliance is safe to plug in and use. Knowing what's involved helps you understand why a landlord's kettle takes two minutes and a commercial catering unit takes considerably longer.

This article breaks down exactly what happens during PAT testing, covering the visual inspection stage, the specific electrical tests engineers run (earth continuity, insulation resistance, and more), and how results determine a pass or fail outcome. We'll also explain why some appliances need different combinations of tests depending on their class and construction.

We've written this from years of testing appliances across London offices, rented flats, and retail units, so you're getting a practical view rather than a textbook one. By the end, you'll know precisely what to expect when an engineer arrives, what each test checks for, and why the process matters for keeping staff, tenants, and customers safe.

Why PAT testing matters for safety and compliance

Landlords, business owners, and property managers all carry a legal duty to keep electrical appliances safe for anyone using them. That duty comes from the Electricity at Work Regulations 1989, which require that electrical equipment is maintained to prevent danger, and the Health and Safety at Work Act 1974, which places a general duty of care on employers. Neither law names PAT testing specifically, but it's the accepted method the Health and Safety Executive points to for demonstrating that appliances have been properly checked. Skip it, and you're relying on hope rather than evidence if something goes wrong.

What happens when checks get skipped

Faulty appliances cause fires. That's not scaremongering, it's what fire investigators find repeatedly in commercial units, HMOs, and offices across London. A frayed cable on a heater, a cracked plug on a kettle, or a damaged extension lead left behind a desk can all sit unnoticed for months until someone gets a shock or a fire starts. PAT testing tests exist precisely to catch these faults before they cause harm, rather than after. Engineers who've worked London properties for years will tell you the same appliances that look fine on the outside often fail on insulation resistance or earth continuity once tested properly.

Regular PAT testing catches the faults you can't see just by looking at a plug.

Insurers take this seriously too. Many commercial and landlord insurance policies now expect evidence of routine electrical safety checks, and a claim following a fire or injury can be refused outright if you can't produce test records. For a landlord with several rented flats, that's a significant financial exposure sitting behind a task that costs relatively little to do properly. For a shop or office, the exposure extends to staff and customers, which brings its own separate set of consequences if the HSE gets involved after an incident.

Who carries the responsibility

Responsibility doesn't sit with the tenant or the employee using the kettle. It sits with whoever owns or manages the property and the equipment inside it. That means:

• Landlords are responsible for appliances they supply as part of a tenancy, such as kettles, toasters, or washing machines left in a furnished let.

• Employers are responsible for every portable appliance staff use, from laptops and monitors to catering equipment in a staff kitchen.

• Facilities managers in commercial buildings often coordinate testing across multiple tenants or floors, keeping one consistent schedule rather than leaving it to individual businesses.

• Letting agents managing properties on behalf of landlords frequently take on the practical task of booking and tracking test dates.

Getting this clear matters because gaps in responsibility are exactly where appliances slip through untested for years.

Compliance also protects you commercially, not just legally. Commercial tenants increasingly ask for proof of PAT testing before signing a lease or renewing one, particularly in shared office buildings where one tenant's faulty equipment can affect everyone else on the floor. Landlords managing multiple rental properties face similar pressure from letting agents who won't market a property without up-to-date safety documentation. None of this is about ticking a box for its own sake. It's about having a paper trail that shows you took reasonable steps, which matters enormously if an incident ever leads to an insurance dispute or an HSE investigation.

Finally, consider the practical side. A tenant who receives an electric shock from a faulty appliance, or a customer injured by a fire in your shop, doesn't care about the technicalities of who owned the equipment. They care that it happened, and so will any solicitor involved afterwards. Testing regularly, keeping accurate records, and acting on any failures promptly is the clearest way to show you managed that risk responsibly rather than ignoring it until something went wrong.

How PAT testing is carried out step by step

A competent engineer follows a set sequence every time, regardless of whether they're testing a laptop charger or an industrial floor buffer. Skipping steps isn't an option because each stage catches different faults, and missing one means an unsafe appliance could still pass. Understanding the order helps you see why a proper test takes longer than a quick glance at the plug.

Step one: the visual inspection

Before any equipment gets plugged into a tester, the engineer examines the appliance by eye and by hand. This visual inspection stage catches roughly 80% of faults on its own, which is why skipping it and jumping straight to electrical readings is a mistake some untrained testers make. They're checking for:

• Cracked or damaged plugs, sockets, and casings

• Frayed, cut, or taped-over cables

• Signs of overheating, such as discolouration or a burnt smell

• Correct fuse rating fitted inside the plug

• Secure cable grips and no exposed wiring

• Evidence of unauthorised or amateur repairs

Any appliance that fails visually gets pulled from service immediately. There's no point running electrical tests on something with an exposed live wire.

Step two: earth continuity testing

Once an appliance passes the visual check, the engineer moves to earth continuity, which applies to Class I appliances (anything with a metal casing and an earth pin, like a kettle or a fridge). The tester sends a small current through the earth wire to confirm it provides a low-resistance path back to the plug. If that path is broken or too resistive, a fault could send current through the casing instead, which is how people get shocked touching an appliance that looks perfectly normal.

Step three: insulation resistance testing

Next comes insulation resistance, which applies to both Class I and Class II appliances. The engineer applies a test voltage between the live and earth (or between live and neutral on double-insulated Class II items) to check that current isn't leaking through worn or damaged insulation. Low readings here indicate insulation breakdown, often invisible from the outside, that raises the risk of shock or fire under normal use.

A proper PAT test only counts an appliance as safe once it's passed every stage, not just the visual check.

Step four: polarity and functional checks

For certain appliances, particularly those with moving parts or heating elements, the engineer also confirms correct polarity (making sure live, neutral, and earth are wired correctly inside the plug) and runs a basic functional check to see the appliance switches on and operates as expected. This stage matters more for kitchen equipment and power tools than for something like a phone charger.

Step five: recording and labelling

Every result gets logged against the appliance's unique identifier, and a pass or fail label goes on the unit itself, along with the retest date. This record becomes your evidence trail if a landlord, employer, or insurer ever needs to prove compliance.

The main types of PAT tests explained

Not every appliance gets the same set of checks. The tests PAT testing tests actually involve depend on the appliance's class, its construction, and how it's powered. Understanding the differences helps you see why a toaster and a floor sander go through different combinations of checks even though both carry the same "PAT tested" label at the end.

Class I and Class II appliances

Appliances split into two main categories, and this split determines which tests apply. Class I appliances have a metal casing and rely on an earth connection for safety, think kettles, microwaves, and washing machines. Class II appliances are double-insulated, meaning they don't need an earth at all, and include most modern power tools, laptop chargers, and plastic-cased fans. Testing a Class II item for earth continuity would be pointless because there's no earth pin to test in the first place.

Leakage current testing

Beyond the basic checks, engineers often run a leakage current test, which measures how much current escapes to earth during normal operation. Small amounts are normal and safe, but excessive leakage signals deteriorating insulation or a fault building inside the appliance. This test matters particularly for equipment that runs hot for long periods, such as catering ovens or space heaters, where insulation breaks down faster under sustained heat.

A leakage current test often catches faults that a static insulation reading misses entirely.

IEC lead and extension cable testing

Detachable power leads, the kind you find on laptops, monitors, and printers, get tested separately from the appliance itself. IEC lead testing checks the earth continuity and insulation resistance of the cable independently, since a faulty lead can make a perfectly safe appliance dangerous. Extension leads and multi-way adaptors go through the same process, and given how many sit coiled under desks in London offices, they're often the items that fail.

RCD and functional testing

Where appliances plug into circuits protected by a residual current device, engineers sometimes verify the RCD trip time as part of the wider test, confirming it disconnects power fast enough during a fault. Functional testing rounds things off by switching the appliance on to check it operates correctly under load, catching mechanical or electrical faults that a static reading alone wouldn't reveal. Together, these tests build a complete picture rather than a single pass or fail snapshot based on one measurement.

How often you need PAT testing and by whom

There's no single legal interval written into law, which surprises a lot of landlords and business owners expecting a fixed number. Instead, the frequency depends on risk, meaning how the appliance is used, where it's located, and how likely it is to suffer damage. A kettle in a quiet office kitchen faces far less wear than a power tool on a building site, so the two shouldn't share the same testing schedule.

Recommended testing intervals by appliance type

Guidance from the IET Code of Practice and widely followed by competent engineers gives a practical starting point, though a risk assessment should always confirm the final interval for your specific setup.

Understanding these bands matters because over-testing wastes money, while under-testing leaves you exposed exactly where risk is highest.

The right testing interval matches how hard an appliance actually gets used, not a fixed date on a calendar.

Who should carry out the testing

Visual checks can technically be done by anyone with basic training, and many businesses build a quick weekly look-over into staff routines for obvious signs of damage. Formal PAT testing, however, needs someone competent, meaning they understand electrical principles, know how to use the test equipment correctly, and can interpret the readings against the relevant standards. This isn't a role for whoever's free that afternoon.

In practice, that means:

• Qualified engineers carrying City & Guilds or equivalent electrical qualifications, ideally with several years testing commercial and domestic appliances

• In-house staff with recognised PAT training certificates, suitable for smaller businesses with straightforward equipment

• Contracted testing companies who handle multiple sites on a rolling schedule, common for landlords with several properties or facilities managers covering large office buildings

Choosing based on price alone rarely ends well. An engineer who rushes through visual checks or skips insulation resistance testing to save time isn't actually saving you anything, they're just deferring the risk to whoever plugs the appliance in next.

Record keeping and retesting

Every test, whether it passes or fails, needs recording against a date and a unique appliance reference. Landlords and employers should keep these records for at least the duration between tests, ideally longer, since they're the evidence you'd produce if an insurer or the HSE ever asked. Retest dates should trigger automatically rather than relying on memory, particularly across a portfolio of rental properties where dozens of appliances might need attention on different schedules throughout the year.

Keeping your appliances safe and compliant

PAT testing tests are never just one quick check. You've seen how a visual inspection, earth continuity, insulation resistance, and leakage current measurements each catch different faults, and how the right combination depends entirely on the appliance's class and how hard it works. Skipping stages or guessing at intervals leaves gaps that only surface when something fails at the worst possible moment.

Getting the schedule right, matching test frequency to actual risk, and keeping accurate records isn't complicated once you understand what each test is checking for. What matters most is having someone competent doing the work, not just someone with a tester in hand. Landlords, employers, and facilities managers who treat this properly protect their tenants, staff, and customers, and themselves, from the fallout of a fault nobody caught in time.

If you'd rather hand this over to engineers who test appliances across London every week, get a quote and we'll sort a schedule that fits your property or business.