Understandably, confusion often exists regarding the difference between Class 2 and Class II rated ac-dc power supplies. The differences are significant and important to understand. The NEC (National Electric Code) identification of Class 2 refers to the output voltage and power capabilities of ac-dc supplies, while the IEC (International Electrotechnical Commission) designator of protection, Class II, refers to a power supply’s internal construction and electrical insulation. Show NEC Class 2 Output Voltage and PowerThe NEC designation of Class 2 is important when installing an electrical system in a building. Class 2 power supply regulations address the wiring requirements (wire size and insulation, wire derating factors, overcurrent protection limits and methods of wiring installation) between the output of the supply and the input of the load. The limited output voltage and power delivery capabilities of Class 2 power supplies are recognized to be of lower risk to fire initiation and causing electrical shocks, which allows for lower cost wiring methods to be employed. Wiring affected by NEC Class 2 power supplyIEC Class II Insulation ProtectionThe IEC protection classes govern the construction and insulation of power supplies to protect the user from electrical shock. In a Class II power supply, there are two layers of insulation (or a single layer of reinforced insulation) between the user and the internal current carrying conductors. In supplies designed with two layers of insulation, the first layer of insulation is typically referred to as “Basic Insulation.” A common example of basic insulation is the insulation present on wires. The second layer of insulation is often an insulating case enclosing the product, such as the plastic case present on wall mount and desktop power supplies. Label showing the IEC protection Class II symbolIEC protection Class II power supplies will have a two-wire power cord as opposed to a three-wire power cord with Safety Earth connection. Products designed with Class II insulation often are labeled as “Class II” or “double insulated” or will have the concentric square symbol on the safety label. Understanding the difference between NEC Class 2 and IEC Class II designated power supplies is a simple, yet important factor in ensuring the correct products are specified in user applications. Ultimately, by selecting a Class 2 or Class II certified power module, you are better protecting your design against electric shock and other hazards and failures that may occur. Safety & Compliance You May Also Like Have comments regarding this post or topics that you would like to see us cover in the future?
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Question There are Power Supplies listed with a "Class 2" UL rating. What is the "Class 2" rating?
The UL Class 2 Power Units standards apply to power supplies within a limited output current and output voltage range.
The Class 2 standard is specified in UL Standard Number UL1310. In order to receive the UL Class 2 approval, the power supplies must pass UL testing as follows: The output current does not exceed 8 A. The output voltage does not exceed 30 VDC.
Furthermore, a benefit of using the power supplies that have received the Class 2 approval is that the output has the same Class 2 safety level. When applying for safety standards approval for the equipment, in some cases it is not necessary to obtain safety standard approval for the connected device (load) when the device (load) is connected to the output of a power supply that has received Class 2 approval. Page 2
The power supply industry uses Class 2 and Class II terminology to refer to two very different types of power supplies. The industry has been using these terms for decades now. So what’s the difference between 2 and II? Is it just a regular number and a Roman numeral? There is more to it. There has always been confusion between Class 2 and Class II. Class 2 relates to the power supply’s safety, and it limits the maximum power that the power supply can deliver. Class 2 power supply is popular in the automation, control, and the power supply lighting industry because of lower safety protection requirements, decreasing complexity and cost during installation. On the other hand, Class II relates to the input of the power supply. Usually, electrical devices have a three-prong plug, of which two pins are live and neutral, and the third being ground. Power supplies with all three connections are called Class I power supplies, and power supplies with the ground connection removed are called Class II power supplies.
What is Class 2 Power Supply?
This is the requirement that covers direct plug-in power supply units intended for connection to a 15-ampere, nominal 120- or 240- volt ac branch circuit. Term class 2 power supply comes from the UL1310 standard section 28, where the AC adapters and power supplies are referred to as Class 2 transforms. Class 2 power supply is also called Class 2 power unit. Similar requirements are also placed in the IEC62368-1 standard, where the reference is made to as Limited Power Source (LPS). By definition, the LPS or Class 2 power supplies are inherently limited power supply units and is an isolated circuit which:
Both IEC 62368 LPS and UL 1310 Class 2 power supply do not allow the apparent power to exceed 100VA, but the maximum current nameplate ratings are slightly different for IEC 62368 and UL 1310. When product safety standards IEC 62368 and UL 1310 are applied to meet class 2 requirements, the power supply output is limited to mitigate the risk of hazardous conditions. By meeting Class 2 standards, the power supply is less prone to starting a fire during an overload condition. Class 2 power supply is also a designation referred to in the National Electric Code (NEC). With the limited power, these power supplies can be used with a less stringent wiring requirement (Class 2 wiring) between the power supply and load, reducing installation costs.
What is Class II Power Supply?
To understand class II power supply, we need to understand Class I supplies first. Roman numerals I and II relate to the input of the power supply. The Class I input power supply allows the use of protective ground conductors as a means to provide safety from electrical shock in addition to insulation and spacings. Class II does not have a ground connection. There are only two connections, namely line, and neutral connection. The safety from electrical shock in the Class II power supply comes from the construction where additional insulation and spacings are added to the power supply construction. Two layers of insulation or a single layer of reinforced insulation between the user and the current-carrying conductor are used to isolate the output and input. Medical standard IEC 60601-1-11 requires that all medical devices for home use that are not permanently installed by licensed personal are Class II. This class II input requirement for medical devices for home settings protects the end-user from electrical shock if they don’t have protective earth-ground wiring or are not functioning correctly. The AC to DC power supply used in home health medical equipment should be Class II to satisfy this requirement. Understanding the significant differences between Class II and Class 2 power supplies is important in order to eliminate confusion and protect the user. These standards were developed to prevent device failure, hazardous conditions and even shock. In order to protect your design make sure you understand these distinction or reach out to us and we will have one of our experts work with you to ensure device safety. Comments are closed |
Class 2 power supply requirements
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