Class 2 power supplies, as defined by the National Electrical Code (NEC) Article 725, are low-voltage power sources with strict output limitations designed primarily for safety and simplified wiring. Unlike general-purpose power supplies, Class 2 units are limited to 100 volt-amperes (VA) maximum for alternating current (AC) outputs, 100 watts for direct current (DC) outputs at voltages up to 60 VDC, and a maximum current of 5 amperes. For AC outputs above 30 volts but not exceeding 60 volts, the power limit is reduced to 100 VA, while for DC outputs between 60 and 250 volts, the current is capped at a low level (typically below 5 mA) to prevent shock hazards.

These limitations are crucial for fire safety and shock protection. The low energy level prevents sustained arcing or ignition of combustible materials, even if wiring faults occur. Because the power is inherently limited, Class 2 circuits can use smaller gauge wires (such as 18 AWG or even 22 AWG) and do not require the same rigorous overcurrent protection or conduit installation as Class 1 circuits. This reduces installation costs and simplifies wiring in applications like LED lighting, security systems, thermostats, and audio systems.

However, these limitations impose design constraints. For example, a single Class 2 supply cannot power high-load devices like large motors or heaters. Multiple Class 2 supplies may be needed for distributed systems, and careful voltage drop calculations are required for long wiring runs. Furthermore, any device connected to a Class 2 circuit must not draw more than the supply's rated output, and wiring must follow NEC guidelines for Class 2 separation from other circuits to maintain its safety classification.

In summary, Class 2 power supply limitations strike a balance between safety and practical installation. By restricting voltage, current, and power, they minimize fire and shock risks while enabling flexible, low-cost wiring. Engineers and installers must respect these limits and select appropriate power supplies and wiring methods to ensure compliance and reliable system operation.