Not all electrical appliances are built the same—and when it comes to Portable Appliance Testing (PAT), understanding the difference between Class I and Class II equipment is essential.
The class of an appliance determines the type of safety checks required, how it’s tested, and ultimately, how safe it is to use. Let’s break it down.
What Are Class I Appliances?
Class I appliances rely on basic insulation plus an earth connection to protect the user. If the live wire inside touches the metal casing, the earth connection carries the fault current safely away, preventing electric shock.
Examples of Class I Appliances:
- Kettles
- Toasters
- Microwaves
- Desktop computers
- Extension leads
Key Features:
- Metal outer casing or exposed conductive parts
- Requires a connection to earth (three-pin plug in the UK)
- PAT testing includes earth continuity and insulation resistance checks
What Are Class II Appliances?
Class II appliances (sometimes called double-insulated appliances) don’t rely on an earth connection. Instead, they use extra layers of insulation to prevent any live parts from touching the user.
Examples of Class II Appliances:
- Phone chargers
- DVD players
- Hairdryers
- Electric drills
- Many modern TVs
Key Features:
- Plastic outer casing (no exposed metal)
- Marked with the double square symbol ⧈
- PAT testing focuses mainly on a visual inspection and insulation resistance—no earth test needed
Why the Difference Matters for PAT Testing
Understanding whether an appliance is Class I or Class II is critical because it changes how the PAT test is performed:
- Class I appliances require earth bond testing in addition to insulation checks.
- Class II appliances only require insulation and visual checks, as there’s no earth connection.
Testing a Class II appliance as if it were Class I could give misleading results—or damage the appliance. On the other hand, skipping the earth test on a Class I appliance could miss a dangerous fault.
Safety Implications
- Class I appliances can become dangerous if the earth wire is damaged or disconnected.
- Class II appliances are generally safer but still need inspection for cracks, worn cables, or faulty plugs.
Both classes can develop faults over time, which is why PAT testing remains essential.
Final Thoughts
The difference between Class I and Class II appliances isn’t just a technical detail—it directly affects how PAT testing is carried out and how safe your workplace or property is.
👉 Next time you book a PAT test, remember: a trained tester doesn’t just check appliances; they understand the class, apply the correct tests, and keep everyone safe.