Class 1 vs Class 2 Appliances: Symbols, Examples & Tests

An appliance’s protection class describes how it protects against electric shock. Correct identification helps a competent tester choose an appropriate inspection and test procedure.

Common categories include Class I (protective earthing), Class II (double or reinforced insulation) and Class III (safety extra-low voltage). Check the actual product rather than assuming its class from its appearance.

The basic concept: how appliances protect you

• Class I equipment uses protective earthing alongside basic insulation. The protective conductor needs to remain effective.
• Class II equipment relies on double or reinforced insulation rather than protective earthing. It can still have accessible metal parts.
• Class III equipment relies on a suitable safety extra-low-voltage supply. Low voltage does not remove every risk, including battery, heat or fire hazards.

See HSE HSG107 for Class I and Class II maintenance guidance and HSE electrical-safety FAQs for voltage and specialist-equipment risks.

How to tell what class an appliance is

Identify the appliance from its rating plate, manufacturer instructions and construction. A metal case, plastic case or three-pin plug alone does not establish its protection class. If the class or suitable procedure is uncertain, stop and seek manufacturer information or a competent specialist; do not guess or default to Class I.

The square-within-a-square marking identifies Class II construction. Inspect the whole assembly, including any separate power supply and detachable lead. Functional earthing and specialist equipment can require additional manufacturer information.

Examples of Class 1 appliances

Desktop computers, kettles, washing machines and some workshop equipment can be Class I. Treat these as examples, not a classification rule: verify the actual product’s markings and instructions.

Examples of Class 2 appliances

Hairdryers, small power supplies and some power tools can be Class II. Look for the appropriate double-insulation marking and manufacturer information; a plastic enclosure alone is not enough to identify the class.

Examples of Class 3 appliances

Some low-voltage lighting and electronic devices use Class III protection. Confirm the marking and supply arrangement. A battery-operated or USB device is not automatically Class III, and its charger or mains supply needs its own appropriate maintenance.

How testing differs between classes

Protective-conductor continuity is relevant to Class I equipment. Class II equipment is not assessed by inventing a protective-earth connection. Both need a suitable visual inspection and any applicable electrical tests.

The competent tester must select a procedure suitable for that specific appliance and test instrument. Test current, voltage, connection points and acceptance limits depend on the equipment and manufacturer instructions. A single 25 A earth test, 500 V insulation test or blanket resistance limit is not suitable for every item. Do not energise equipment with a known defect, or repeatedly test it until a passing result appears.

Use the equipment and tester instructions alongside the applicable Code of Practice. HSE distinguishes trained visual inspection from the greater knowledge needed for testing.

Class 1 test sequence

Class I equipment relies on a protective-earth path. The competent tester selects the applicable continuity and other checks using the equipment and instrument instructions. Do not use a generic numerical threshold as a substitute for that procedure.

Class 2 test sequence

Class II equipment does not rely on protective earthing for shock protection. Choose the appropriate insulation or leakage assessment from the product and instrument instructions; do not invent an earth test for the enclosure.

Substitute leakage test for Class 2

Substitute leakage and tests performed with equipment operating are different methods. Their suitability depends on the equipment and instrument. Sensitive electronics do not make one alternative universally correct.

Common confusions

Neither a metal case nor a plastic case is a reliable class label. A metal earth pin also does not prove that an appliance uses protective earthing. The class must be established from reliable product information.

Treating an unknown item as Class I is not a safer default. A wrong test sequence can produce misleading results or damage equipment.

Special cases

Detachable mains leads and power supplies should be identified and covered by the maintenance system. Their tests depend on their own construction, connections and manufacturer instructions. Not every detachable lead has an earth conductor.

An unidentifiable, altered or obsolete appliance should be referred for competent assessment before use. Do not assume that a successful tester indication establishes suitability.

How class affects testing frequency

Choose inspection and test intervals from the equipment, environment, use, manufacturer instructions and previous findings. There is no universal annual PAT interval. HSE explains the risk-based approach.

The IET removed the old frequency table from the fifth edition of its Code of Practice; it did not replace it with a new set of fixed intervals. Read the IET explanation.

Frequently asked questions

Are all laptop chargers Class II?

No. Power supplies vary; some use a protective-earth connection. Check the rating plate and manufacturer instructions for the actual model.

Can Class II equipment have metal parts?

Yes. Enclosure material alone does not define the insulation system.

What should I do if I cannot identify the class?

Do not guess. Obtain manufacturer information or ask a competent specialist before selecting tests or returning uncertain equipment to use.

The takeaway

Identify the equipment correctly, then choose a suitable test procedure. Training should help you recognise the limits of your competence as well as carry out appropriate checks.