Every appliance that uses mains voltage must provide at least two levels of protection. This is so that in the event of one layer failing, the backup layer can be used. This makes electric equipment extremely safe. You can choose to have appliances classified as Class 1 or 2.
It is crucial to identify the class of the appliance before performing PAT testing. Class 1 appliances are not tested the same way as Class 2.
Electrical appliances can be classified into five types of equipment construction, which are Class 1, 2, 3 and 0. The most important of these are Class 1 and 2. All Classes are listed below for completeness.
Insulation and the use of the mains earth provide protection. This can be best demonstrated by using an electric fire that has been dismantled.
The three wires that connect to the EARTH, NEUTRAL, and LIVE pins are found in the open plug. The brown LIVE and blue NEUTRAL wires connect to a connector inside the fire. The metal case houses the green/yellow earth wire.
The connector’s plastic insulation protects the user from electric shock. This protects the LIVE and NEUTRAL cables from being tangled in the case. Basic insulation is the name given to this plastic insulation.
If the basic insulation fails, such as when the cable touches the metal case too much, the user can get an electric shock.
The EARTH wire connects to the metal case of an electric fire and keeps it at EARTH potential. This means that an electric shock cannot be generated even if the metal firebox is connected to the LIVE voltage. Practically, a fuse would blow in either the main fuse box or the plug to protect the user.
The protection of Class 1 appliances is a combination of basic insulation, and an EARTH connection. This provides two levels of protection.
The Earth Continuity, Insulation Resistance and Earth Continuity tests are performed when PAT Testing Class 1 appliances are being tested.
A Class 2 appliance is equipped with at least two layers insulation. Class 2 appliances are sometimes called Double Insulated. They don’t require an Earth connection.
This can be seen best by opening up a Class 2 electric drill. The drill’s plastic enclosure provides additional insulation in addition to the basic insulation provided by the connector.
Two layers of insulation are applied to protect the user. Only the Insulation Resistance test will be performed when PAT testing Class 2 appliances.
The double box symbol is always used to indicate class 2 appliances on the rating plate.
Equipment constructed to Class 3 standards are intended to be supplied by a special safety transformer, whose output is called Safety Extra-Low Voltage (SELV). It must not exceed 50 V AC, and should be below 24V or 12. A special symbol is used to identify Class 3 appliances. In Class III appliances, there is no need for an Earth.
Safety isolating transformers are designed to ensure electrical safety for Class 3 appliances. The separation between windings is equivalent of double insulation. This transformer is suitable for Class III appliances.
CLASS 0, & 01
This equipment is not intended for use in residential or business settings. This equipment is only for informational purposes.
Appliances in class 0 rely only on basic insulation to protect against electric shock. They are therefore not permitted to be sold as they don’t have two levels of protection. This brass lamp is an example of a metal-cased, two-wire appliance that has only basic insulation. The bulb holder does not have an earth connection.
An Earth connection is possible for Class 01 appliances. However, it is wired with twin core cable or a 2-pin plug. Therefore, an Earth connection cannot be made. As in Class 0, one can only rely on basic insulation to protect against electric shock. They only offer one level of protection so Class 01 appliances cannot be sold.
These appliances can be thrown out if they are found during PAT testing.
CLASS I & II APPLICATION
It is important to distinguish between Class 1 and 2 appliances when PAT testing is done. This confusion is magnified by the many myths that surround PAT testing. These myths can be helpfully listed.
If the fuse is in the plug, it must be of Class 1.
It’s made of metal, so it must be Class 1.
This case is made of plastic, so it must be Class 2.
It is a three-core cable, so it must be Class 1.
The plug is Class 1 because it has a metal earth pin.
None of these statements can be used to correctly identify Class I or Class II appliances. Some are misleading.
This is the easiest rule to follow.
The appliance is class 2 if it has a double-box rating plate. If the rating plate does not have a double box, then the appliance is Class 2.
Example – Kettle
This kettle’s rating plate clearly does not have the “double-box” symbol. According to our rule, it must therefore be Class 1. The plug’s earth connection terminates at the outer metal casing of the heating elements. The Earth Continuity and Insulation Resistance tests must be performed when PAT testing the kettle.
Example: Plug-top power supply
This Plug-top transformer’s rating plate clearly displays the “double box” symbol. It is therefore a Class 2 appliance. It does not have a plastic Earth pin as it is not required for Class 2. Not all Class 2 appliances require a plastic Earth pin. Only the Insulation Resistance test must be performed during PAT testing.
Example – Mains extension
This extension’s rating plate is made of plastic. It does not appear to have the “double-box” symbol so it must be Class 1. This extension lead must be tested for Earth Continuity and Insulation Resistance when it is subject to PAT testing.
Example – Table lamp
This table lamp is classified as a Class 2 appliance because the rating plate clearly indicates that it has a “double-box”. This is a Class 2 appliance, which is mostly in a metal enclosure. The required double insulation is provided by the bulb holder, which is made from plastic. Only the Insulation Resistance test must be performed during PAT testing.
Example: Desk fan
This fan’s rating plate does not include a symbol for a double-box, but it also states that the appliance must have an earth connection. This appliance is clearly classified click this link to learn more as a Class 1. It does not contain any metal that can be accessed by the user.
Example: Metal Lamp
This metal lamp would have a rating plate and be classified as a Class 1 appliance if it had an earth point on its lamp holder. This would be impossible because the rating plate is missing.
Are Class 1 appliances as safe as Class 2?
Both are safe to use as they have two levels of protection.
The earth connection is an additional layer of safety for Class 1 appliances. To ensure that this is effective, wiring must be checked regularly to make sure the earth connection in the mains socket matches the local earth potential. This can be done by either removing the earth sheathing from the mains cable entering the premises or driving a stake into the ground. To provide Class 1 protection, appliances must be connected to the outside wiring.