When PAT testing, different types of test are performed depending on the particular class an appliance falls under.
Basically, during manufacture, a portable appliance is given a class rating depending on how the user is protected from electrical shock. Any portable appliances without a class rating should be treated as a Class 1 appliance.
If an appliance uses mains voltage, it has to provide two levels of protection to the user. Many have more, but 2 is the minimum. By having more levels of protection, this ensures the appliance remains safe even if the first level fails.
Electrical appliances are currently categorised into either Class I, Class II, III, 0 or 01. You can read more on each class below.
Class I
The protection inside class 1 appliances combines together the protection of insulation and a means of connection to the earth connection protective conductor (Earth wire).
This means that the user is protected from electric shock because of the plastic insulation of the wiring. If this fails and the casing of the appliance were to become live then the casing of the appliance will be as close to zero potential as possible.
Electricity always tries to take the path of lowest resistance to earth and therefore if someone were to touch the casing of the appliance, the body of that person would provide a higher resistance to get to earth than that of the earth cable.
Any fault current would therefore flow down through the earth cable and not the user.
For Class I items, you just need to remember they offer two levels of protection. Remember:
- Basic Insulation
- Earth wire
The symbol for Class I items looks like this, and should be found somewhere on the appliance.
Some examples of class 1 appliances are toasters, kettles, washing machines and irons.
Class II
These appliances are known as double insulated due to the presence of at least two layers of insulation. The earth connection present in Class I appliances is not required for safety.
Examples of class two appliances include things such as hedge trimmers, lawn mowers and drills. Often they’re constructed with insulated wiring inside, as well as extra insulation because of the device’s plastic case.
Class II appliances are represented by a square within a square symbol like this. This is generally found on the appliance label where the volts and power are indicated.
Class 0 and 01
A much rarer form of equipment, these kinds of appliances are generally not found with business and residential environments.
Class 0 appliances depend only on basic insulation without a provision for earth. If it fails, it is entirely dependant on the environment around it to remain safe.
Class 01 appliances do have room for an earth connection, but it is wired differently either with twin core cable or only has a 2 pin plug. This appliance is also dependant on one level of insulation.
Class 0 and 01 appliances have been effectively banned in the UK since 1975.
Identifying an Appliance Class
Generally, the easiest way to identify an appliance is simply to look at the symbol. For PAT testing, you’re more than likely only going to be testing Class I/II appliances, so you can easily identify each of these by the symbol on the appliance itself.
As a rule of thumb, check to see if the appliance has a rating plate. If it doesn’t, it instantly fails. If it does have one, and has a double box mark, it’s a class II appliance. If it doesn’t have the square within a square symbol treat it as a Class 1 appliance.
Written by Barry Atkins
