How equipment is classified is important as it determines the inspection criteria required for the equipment. Ultimately, these classes are determined by the design factors that provide user protection.
Electrical appliances use two methods to ensure users safety:
- Basic Protection – This should be a fundamental design aspect of any appliance. It ensures that any live part of the appliance is insulated and covered to prevent users from being able to touch them.
- Fault Protection – This is a mechanism that protects users in instances where parts of an appliance have become unintentionally live because of a fault. This usually comprises reinforced or double insulation and/or the “Earth Wire”. This wire provides a low-resistance path to the ground that diverts live current from passing through a person.
For PAT testing, there are three relevant classes of equipment.
Class I – This class relies on the insulation of live parts to protect against accidental contact with live components. Additionally, they are earthed to provide protection in cases where a fault has caused the outer casing to become live, and the casing is made from conductive materials.
Examples of Class I equipment include coffee machines, desk fans, and kettles.
Class II – This class of equipment relies on insulation to protect the user in the case of a fault occurring. The insulation is either of the double insulation type or reinforced insulation. This class of equipment does not rely on an earth connection to protect the user in the case of a fault. Rather the enhanced insulation ensures that electricity cannot reach any part of the equipment where it has the potential to cause harm.
Class II equipment can be identified by a double square symbol on the appliance. Examples include Lamps, TVs, Hair Dryers, Power tools, etc.
Class III – This class relies on protection from a Separated Extra-Low Voltage Supply (SELV). This is usually less than 120vdc or 50vac, and at such low voltage, testing is not required. However, in cases like mobile phones and laptops which fall into this category, the chargers or power supplies will require testing.