Industry Article

Understanding the Safety Standards for Smart Appliances

August 05, 2021 by Ron Stull, CUI

Which IEC power standards should you be familiar with when designing smart appliances? This article breaks down smart household device classification and power requirements for their design.

The market of smart devices is, without a doubt, continuing to grow rapidly, and so is the smart appliance sector. According to Statista, the revenue in the smart appliances market segment is expected to reach $38.4 billion this year, with 262 million households predicted to be using smart appliances by 2025. And the types of smart appliances available have expanded to include microwaves, refrigerators, thermostats, ovens, air fryers, ice makers, and pressure cookers.


Figure 1. (Left) Smart fridge with hi-def display. (Right) Smart washer and dryer with Wi-Fi connectivity.


The use of smart devices and IoT (Internet of Things) are growing throughout the house as well, extending from smart doorbells for the front door to even more advanced smart thermostats that can optimize energy usage and smart refrigerators that can alert you when certain items are running low. 

Smart household appliances must comply with a different set of standards than other smart devices, and compliance with those standards must start during the design phase. In particular, compliance with the right power-related standards is critical for success in the growing smart household appliance market.

Identifying and following the appropriate standard as early as possible in the design phase can simplify decision-making and shorten time-to-market.


Smart Household Appliances

Household appliances are not as simple as they were in the past, and they are rapidly taking advantage of IoT (Internet of Things) capabilities and intelligent systems. Appliances can have graphical displays and wireless connectivity that makes them very similar to ITE (Information Technology Equipment) applications, but they do differ from smart devices classified as ITE, ICT (Information and Communications Technology), and AV (Audio Video). 

The primary differences lie in how they are used, who the users are, where they are used, and how users can interact with them. For example, smart televisions classified as smart appliances, found in the living rooms and bedrooms of people worldwide, have made it much easier to take advantage of live and streaming entertainment. However, unlike televisions of the past, smart televisions depend heavily on data connections. 

On the other hand, smart refrigerators are found in the kitchen where they can make decisions based on artificial intelligence and communicate with other devices and apps to accomplish tasks that include sending alerts to users that certain products are running low or making orders on behalf of users. 

Smart household appliances can be programmed by the user and provide automation at some level (e.g., turn the coffee maker on at 6 a.m. or set the thermostat to a higher temperature when everyone is gone from the house), but also make decisions on their own via artificial intelligence (e.g., adjust the thermostat settings to minimize energy consumption). This type of usage may involve more interconnectivity than traditional smart devices and involves multiple interfaces (i.e., interacting with users, interacting with other devices, communicating with applications). And the key to determining the correct approach to design and powering such devices lies in the IEC 60335-1 standard.


Safety Standards for Household Appliances

The safety standard for home appliances (including smart home appliances) is IEC 60335-1, which is similar in some ways to IEC 60950 and IEC 62368-1. However, to account for smart household appliances, the IEC 60335-1 standard recognizes that modern household appliances may be internet-connected and are likely to have electronic, as opposed to manual, controls. 

Newer standards, including IEC 62368-1, focus on Hazard-Based Safety Engineering (HBSE). This means that potentially hazardous energy sources and the mechanisms that could allow energy transfers from occurring are identified, and measures are taken to prevent them. And not only are safeguards put into place but their effectiveness must be evaluated.


Harmonization of Standards

Harmonizing standards for household appliances, including smart models, is quite challenging. IEC 60335-1 has, in North America, been used as the basis for a tri-national standard between Mexico (NMX-J-531/1-ANCE), the United States (UL 60335-1), and Canada (CAN/CSA-C22.2 No. 60335-1). Note, however, that the United States does not recognize all of the 100+ part 2 standards of UL 60335 related to specific products. Unlike the United States, the European standard EN 60335-1 does recognize most of the part 2 standards.


Comparing IEC Power Standards: IEC 60950, IEC 62368, and IEC 60335

There are some differences between IEC 60950, IEC 60335, and IEC 62368 in the context of power supplies, and it is often true that the best way to become familiar with a new standard is to compare it to an existing standard. In most cases, IEC 60335 is more stringent than IEC 63268 and its ubiquitous predecessor, IEC 60950. The following compares IEC 60335 with the well-known benchmark 60950 standard for information technology equipment, all in the context of power supplies and external adapters.


Current Leakage Requirements

Consider current leakage: The IEC 60335 standard limits leakage current to 0.75 mA for portable appliances and 3.5 mA for stationary appliances. 

IEC 60950, however, has three different categories (hand-held, movable, and stationary), and the leakage current for all three of these (including portable) is the same as what IEC 60335 requires for stationary appliances: 3.5 mA. 


Creepage Requirements

Creepage requirements for working voltages between 250 VAC and 300 VAC with reinforced insulation are as follows: IEC 60950 requires 6.4 mm while IEC 60335 requires 8.0 mm. Keeping in mind that creepage, as shown in Figure 2, refers to the shortest path along the insulation surface between two conductive parts, IEC 60335 is more stringent. 


Figure 2. (Top) Example of clearance distance. (Bottom) Example of creepage distance.


However, for clearance (which is the distance between two conductive parts through air) under the same working conditions, IEC 60950 requires 4.0 mm, and IEC 60335 requires only 3.5 mm.


Isolation Voltage Requirements

Another example of differences lies in the isolation voltage, which refers to the maximum voltage applied for a short period between a power supply's input and output or chassis. 

IEC 60950 defines a fixed value for input-to-output isolation of 3 kV, and a maximum output-to-ground working voltage of 500 V. IEC 60335, on the other hand, only defines an input-to-output isolation voltage requirement of 2.4 kV + (Working Voltage x 2.4) with no maximum output-to-ground working voltage.


Meeting IEC 60335-1 Standards with CUI Power Supplies

Finding the right power supply that meets the correct set of standards is vital to success in the growing (and highly competitive) smart appliance market. However, navigating through the IEC 60335-1 standard to make sure the power supply or adapter is fully compliant can be challenging.

CUI’s power supplies are designed to meet the stringent standards of IEC 60335-1. The first is the PBO-3C/5C/10C Series (3-10W), shown in Figure 3, which are open frame board mount AC-DC power supplies in an ultra-compact SIP package. Not only are they suitable for applications with limited space, but they are also economical solutions for applications with low power demands.


Figure 3. (Left) PBO-3C, (Middle) PBO-5C, (Right) PBO-10C.


The next product line is the PSK-3D/5D/10D/15D/20D/25D Series (3-25W) of encapsulated board mount AC-DC power supplies with a compact design, an input voltage range between 85 and 305 VAC, and a wide operating temperature range. 

Finally, the VOF-100C/120C/180C/200C/225C/350C Series (100-350W) of power supplies are also open mount AC-DC power supplies. They are designed to reduce the standby power consumption and overall power consumption and are certified to IEC 62368, 60335, and 61558.

CUI’s website provides a variety of tools and resources needed to find IEC 60335-1-qualified power supplies. It also offers materials such as application notes, videos, and more. 

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