The evolution of home appliances, IoT (Internet of Things), and the smart home concept has made the safety aspect more important than ever. Devices that were once relatively basic, now include a variety of extra functionalities, such as graphic displays, wireless communication, software interfaces, touch screens,… All these extra features imply additional electronic circuits and specific power supplies, influencing the overall safety of the product.
IEC/ EN 60335-1 is part 1 of an international standard that addresses the general requirements for electrical/electronic appliances for household and similar purposes. The standard covers devices with input voltages up to 250 VAC for single phase nets and up to 480 VAC for multi-phase nets, as well as battery operated equipment. In addition to the general requirements of part 1, there is a part 2 of the standard which covers additional requirements for some specific device types, such as dishwashers, covered in IEC/ EN 60335-2-5. Due to the variety of appliances that may be found in a household environment, over 100 device types have been listed in part 2.
Illustration of smart appliances – fridge and toaster
Figure 1: (Left) Smart fridge with hi-def display and wi-fi connectivity. (Right) Smart toaster with LCD touch screen.
In Europe the harmonized standard is EN 60335-1 and defines how appliances may comply with European directives, such as the low voltage directive. Unlike the United States, the EU recognizes most, if not all, of the 100+ part 2 standards related to specific products.
In North America, IEC 60335-1 has been used as the basis for a tri-national standard between the United States (UL 60335-1), Canada (CAN/CSA-C22.2 No. 60335-1), and Mexico (NMX-J-521/1-ANCE). In the US, UL 60335-1, which is in its 6th edition, is harmonized to IEC 60335-1 as part of its participation in the HOUS category of the IECEE CB Scheme. However, the United States does not recognize all of the part 2 standards. The part 2 requirements take precedence over the general requirements laid out in part 1.
When assessing a new standard, it is helpful to compare the requirements with a standard that is already familiar. Perhaps the most common product category for power supplies and adapters is that of information and technology equipment (ITE). This category, which was standardized to IEC/ EN 60950, and now IEC/ EN 62368, tends to be the benchmark to which most other power supply standards are compared. Below we will compare some common requirements that can impact the design of a power supply.
One of the first differences is in the creepage and clearance distances. Creepage is the shortest path between two conductive parts along the surface of the insulation (Figure 2). Clearance is the distance between two conductive parts through air (Figure 3). The requirement for each is dependent on the working voltage and insulation type (basic vs reinforced). In many cases the requirements are the same, but in certain cases the requirements may be more or less stringent. For example, IEC/ EN 60950-1 requires 6.4 mm of creepage for reinforced insulation when the working voltage is between 250 VAC and 300 VAC, whereas IEC/ EN 60335-1, under the same conditions, requires 8.0 mm. However, the clearance requirement for the same situation is 4.0 mm for IEC/ EN 60950-1 and only 3.5 mm for IEC/ EN 60335-1.
Figuur 2: Creepage distance
Figuur 3: Clearance distance
Another difference is in isolation requirements. The isolation voltage is the highest voltage that may be applied between a power supply’s input and output or chassis for a short time. Above this value the insulation may break down and current will begin to flow. Isolation voltage is not to be confused with working voltage, which is the maximum voltage that may be continuously applied across an isolation barrier. The isolation voltage required is dependent on the location of the isolation: input to output, input to ground, or output to ground. For IEC/ EN 60950-1 there are fixed values for each, with the input to output requirement being 3 kV. IEC/ EN 60335-1’s requirement depends on the working voltage. For example, the input to output rating is 2.4 kV plus the working voltage multiplied by 2.4. Also, for the output to ground requirement, IEC/ EN 60950-1 requires 500 VAC whereas IEC/ EN 60335-1 has no requirement.
Leakage current is current that flows in the protective earth conductor or chassis. When there is no ground connection or it is broken, this leakage current can flow through the human body and thus it is important to limit. When it comes to leakage current there’s not only a difference in the allowed current, but also in how the devices are classified. IEC/ EN 60950-1 classifies devices as hand-held, movable, or stationary, while IEC/ EN 60335-1 identifies two categories: portable appliances and stationary appliances. Portable appliances have the same requirements as hand-held devices (0.75 mA), while stationary and movable devices of IEC/ EN 60950-1 have the same requirements as the stationary appliances of IEC/ EN 60335-1 (3.5 mA).
The added complexity of modern household appliances leads to a greater number of potential faults that may occur, some of which may affect other safety provisions within the device. In recognition of this IEC considers not just single faults, but faults in conjunction with other faults. The environment in which an ITE device is used may be much different than a household appliance, especially when it comes to the presence of water. Depending on the appliance, there is a probability that some amount of moisture may be present in or around these devices. To account for this IEC/ EN 60335 has a moisture resistance requirement, known as the IP rating, describing the protection an enclosure provides from solids and liquids. The requirement is dependent on the appliance classification as defined in IEC/ EN 60529.
The increasing number and growing complexity of smart household appliances has increased the number and types of devices subject to the IEC/ EN 60335-1 standard. As devices have evolved so has the safety standard, with newer editions and an increased number of devices called out in part 2.
As a power supply specialist we can advise you and offer you the power supply designs you need to meet the IEC/EN 60335-1 general requirements as well as solutions in accordance with IEC/EN 61558-2.