One of the fist things new PAT Technicians learn is to identify the difference between Class I and Class II equipment. This is important as it helps to determine which electrical tests need to be carried out on appliances.
Equipment manufacturers are required to construct electrical equipment in ways which mean that users can’t come into contact with internal live parts and any exposed conductive parts that may become live if a fault develops.
There are four different types of classification of equipment, Class 0, Class I, Class II and Class III. Class 0 equipment has no protective earth connection, has a single layer of insulation and is a type of equipment not permitted in the UK due to safety concerns.
Class I equipment is constructed through the connection of the exposed conductive parts to the earth of the installation via a protective conductor. This means that if a fault occurs, Class I equipment is dependent upon the protective device and conductor arrangements of the electrical installation itself. Class I equipment includes things like photocopiers, domestic white goods and kitchen appliances.
Class II equipment is constructed with either, insulation around the live parts of both basic and supplementary insulation or with reinforced insulation. Reinforced insulation can be single layer of insulation or could be a few layers of insulation that cannot be tested singly as basic insulation or supplementary insulation. Class II equipment does not rely on the fault protection of an installation like Class I equipment does, but instead requires a protective conductor.
Some types of Class II equipment have metallic casings but these casings don’t need to be earthed as the insulation on Class II equipment prevents it from becoming live in the event of a fault. Types of Class II equipment include power supply units and most mains powered tools and garden equipment.
Class III equipment is constructed to provide protection against electric shock through limiting the maximum nominal voltage to a 50Vac or 120V ripple-free dc. Class III equipment does not need electrical tests to ensure its safety.
Some items of equipment are not marked with a symbol to determine their class; these types of equipment should be thought of as Class I. This is also relevant to extension leads because if a fault develops on a Class I appliance connected to the lead, it will then rely on the conductor within it for safety.
Once Class has been established, appropriate tests for that particular equipment class can be carried out. Some of these tests are not possible without first identifying what class of appliance it actually is.
Written by Sara Thomson
