What is The Difference Between Class 2 and Class II Power Supplies?
Shopping for power supplies can be difficult because there are many options available and regulations you must follow depending on your project. You might have come across certain regulations that require a Class 2 or a Class II power supply but not know what they refer to. These two classifications may sound similar, but they mean two different things. Class 2 refers to the wiring requirements and power capabilities, while Class II refers to a power supply’s internal build and insulation.
NEC Class 2 Power Supply
For a power supply to be labeled as Class 2, it must meet the standards laid out in Article 725 of the NFPA 70 National Electric Code (NEC). These standards cover the wiring requirements and power limitations of AC/DC power supplies to reduce the risk of shock or fire. You may also see UL 1310 come up in reference to NEC Class 2 circuits. While the NEC defines the installation and power limits for Class 2 circuits, the UL 1310 serves as the standard that Class 2 power supplies must be built to.
Class 2 Wiring
All Class 2 power supplies must meet the NEC overcurrent protection and wiring sizing regulations. Class 2 power supplies must be constructed with ‘In-Wall’ Rated wiring meant for permanent installation inside walls or floors, where they may be surrounded by insulation. These wiring requirements help prevent cracking or melting of the wire, which could become a dangerous fire hazard.
Class 2 Power Limitations
To be considered Class 2 compliant, power supplies must have a maximum power capacity of 100VA and cannot exceed a 30V AC or 60V DC output. The specific maximum wattage and current rating for a power supply will depend on the output voltage. For example, a 12V DC power supply has a 60W maximum and a max current rating of 5A, while a 24V DC power supply has a maximum wattage of 100W and a 4.16A max current rating. These limitations are put in place to lower the risk of electric shock or overheating from excessive currents.
For projects that require a large amount of power, you can either install multiple power supplies or a high-wattage multi-tap power supply. High-wattage multi-tap power supplies, like this 240W 24V power supply, contain 4 separate 60W outputs. Each output has its own circuit breaker, so if one of them were to experience a power surge, the other outputs wouldn’t be affected. You could achieve the same power output by installing multiple 60W 24V power supplies on the same circuit. However, using a large power supply when needed is a more affordable solution and easier to install than multiple power supplies.
Class 2 power supplies are often identified with the words “Class 2 Power Supply” on the label of the power supply.
IEC Class II Power Supply
For a power supply to be considered Class II, it must follow the design laid out in IEC 61439-1 of the International Electrotechnical Commission. This code details that Class II power supplies must have two layers of insulation between the user and the internal current-carrying components to protect the user from electrical shock. The first layer is considered a “basic” insulation, and the second layer is often referred to as a double, reinforcement, or supplemental layer. This reinforced insulation eliminates the need for a protective earth connection (earthing) or a ground connection since the power supply is grounded within the product’s casing.
Class II power supplies can be identified on the label by a symbol of a large square with a smaller square inside of it. Some examples of Class II power supplies are laptop or phone chargers with a two-wire power cord.
