It is important to be able to identify Class I and Class II and Class III appliances when undertaking PAT testing. The tests carried out, the frequency of tests and the PASS/FAIL limits all depend on this. The table below gives more detail of this.

	Class I	Class II
Protection	Uses basic insulation and Earth connection to protect the user.	Uses double insulation (ie basic and supplementary) to protect the user.
How to identify?	Use of an earth connection. Absence of the “double box” symbol.	"Double box” symbol on the rating plate.
Construction	Majority of metal construction though not exclusively.	Majority of plastic construction. May have parts made of metal.
Examples	PC, Electric fire, Kettle	Drill, Hairdryer, Video player
Which is safer?	Depends on the provision of Earth for protection. So Class I is not as safe as Class II.	There is no dependence on outside factors for safety. Class II is inherently a lot safer than Class I.
Earth Bond/Continuity test	Needs to be done to check that this connection is available and is of a low value.	Not applicable to Class II.
Insulation Resistance test	Needs to be carried out.	Needs to be carried out. Pass limit is higher than for Class I.

Class III equipment relies on the supply from a separated extra-low voltage source (SELV) such as an isolating transformer to EN 61558. Class III equipment carries the symbol below.