Quick Hits

⚡ NEC Quick Hit: Class 2 & 3 Power Sources (Tables 11(A) & 11(B)) ⚡ 

Working with low-voltage control circuits, thermostats, or security systems? Chapter 9 Tables 11(A) (AC) and 11(B) (DC) spell out the exact voltage, current, and power limitations for Class 2 and Class 3 sources. Let's break it down! 👇

SLIDE 2 (INHERENTLY LIMITED VS. NOT INHERENTLY LIMITED) The Two Categories of Low-Voltage Power:

• Inherently Limited (Overcurrent Protection NOT Required):

  • The transformer or power source naturally restricts current and power under a short circuit or fault.

• Not Inherently Limited (Overcurrent Protection REQUIRED):

  • Can deliver higher energy levels; requires a specific combination of the power source and an external overcurrent device (like a fuse or circuit breaker) at the supply point.

SLIDE 3 (CLASS 2 VS. CLASS 3 VOLTAGE LIMITS) Where Do the Boundaries Sit?

• Class 2 Power Sources:

  • Capped at 30V max for standard sinusoidal AC (and continuous DC) in indoor/dry locations. Designed for general low-energy signaling and control.

• Class 3 Power Sources:

  • Extends up to 100V AC (and up to 150V DC for specific not-inherently limited configurations) for applications requiring higher voltage capacity.

SLIDE 4 (FIELD TAKEAWAY & WRAP-UP) 💡 Apprentice Pro-Tip: 

Always check the nameplate! Class 2 and Class 3 power sources must be durably marked with their class and electrical rating. If your source is not inherently limited, never bypass or omit that required overcurrent protection device at the supply point!

💬 Save this post for your next low-voltage or control panel rough-in! 🔗 More code breakdowns & study tools at www.JoshTheSparky.com

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