Classification types of appliances: Class I appliances, Class II appliances and Class III appliances

    Electrical appliances are an essential part of modern society. From mobile phones to coffee machines, we use them all the time. Because of the potential dangers of electricity, it is important that they are inspected and tested to ensure public safety.

 

    To protect consumers and domestic animals from electric shock, the International Electrotechnical Commission (IEC) publishes IEC 61140, a basic safety publication standard, to provide guidelines for technical committees when publishing their own publications. IEC is an international standards organization that develops international electrotechnical standards. Electrotechnical technology is the science of how electric current is used in technology, and electrical appliances fall into this category.

Before being released to consumers, electrical appliances must undergo portable appliance testing (PAT). To determine the type of PAT test that applies, the IEC 61140 standard divides appliances into several protection categories. This article will explore the characteristics of each appliance category.
Symbols for Class I, II, and III appliances. From Wikipedia.

Class I appliances

Class I appliances are usually made of metal, have three cables, a metal earth pin, and a fuse in the plug. However, the only way to confirm if a device is a Class I appliance is to see if it has the Class I appliance symbol on it.

Class I appliances include refrigerators, microwaves, kettles, irons, toasters, etc.

Class I appliances have two levels of protection: basic insulation and earth. Inside these appliances there are three wires connected to three different pins. The three wires are called live, neutral, and earth. They are usually brown, blue, and green/yellow (green is used in the US, Canada, and Japan).

 

From Wikimedia Commons.

Electricity travels from a power source to an appliance through a circuit. If the circuit is functioning properly, power flows from the power source to the appliance and back to the power source. The hot wire provides the current to the appliance. The neutral wire conducts the current back to the power source. The ground wire allows the current to flow to the ground in the event of a short circuit.

From Wikimedia Commons

The live and neutral wires are connected to plastic connectors. The plastic connectors secure them from touching the metal housing. This separation is called basic insulation. If the live or neutral wire touches the metal housing, a circuit fault will occur.

If the basic insulation fails, the grounding circuit provides the next level of protection. The grounding circuit provides protection using a ground wire connected to the metal housing. Without the ground wire, the current will pass through the end user's body. As a result, the end user may receive an electric shock. To prevent such accidents, the ground wire leads the current to the ground. At this time, the fuse in the plug or fuse box melts, or a power trip occurs.

Class I appliances are subject to two PAT tests, ground continuity and insulation resistance tests, which are used to check the basic insulation and ground connection.

Class II appliances

Class II appliances usually have plastic housings. The only way to accurately identify these appliances is to look for the Class II appliance symbol. Examples of Class II appliances include hair dryers, DVD players, televisions, computers, copiers, etc.

Class II appliances have two layers of insulation. Like Class I appliances, the plastic connector provides the basic insulation. The additional layer of insulation is the plastic housing, which provides backup protection. The double insulation eliminates the need for grounding.

 

 

 

From Wikimedia Commons

These appliances only require insulation resistance testing.

The Class II classification is sometimes confused with the Class 2 designation; however, the two are not the same. The Class 2 label is related to power, not safety, and is based on a different standard, UL 1310.

Class III appliances

Class III appliances are identified by the Class III appliance symbol.

Class III appliances include laptops, mobile phones, and low-energy light bulbs.

Class III appliances use an isolation transformer consisting of two separate coil windings, called the "primary winding" and the "secondary winding", the former connected to the power supply and the latter to the appliance. Each winding covers opposite sides of a conventional closed magnetic circuit called the "core", and each forms a loop, called the primary loop and the secondary loop. The two sets of coils do not touch each other and are isolated from each other, so this transformer is also called an isolation transformer. The two sets of windings that are isolated and do not touch each other form insulation, and the two sets of coils form a current through the induced voltage.

 

Image of an isolation transformer. From Wikimedia Commons.

 

Basic transformer circuit. From Wikimedia Commons.

Class III appliances do not require grounding. Since there is no grounding protection, when a fault occurs in the circuit, the current is cut off and cannot continue to flow. Therefore, the end user will not receive an electric shock.

Class III appliances do not require PAT testing unless the charging lead falls into the category of Class II appliances. If used for medical purposes, Class III appliances are not safe enough for general consumer use and must meet additional requirements.