The Difference Between Class 2 and Class II Power Supplies

The Difference Between Class 2 and Class II Power Supplies: The Ultimate Guide

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:

1. Cannot provide more than 100VA of continuous apparent power under any loading condition
2. Cannot supply substantial current under a short circuit condition
3. Has a SELV compliant open-circuit voltage of 60V DC or 42.4V peak AC max

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.