Class 2 Remote-Control, Signaling and Power-Limited Circuits
Class 2 circuits include doorbells, thermostats, low-voltage lighting controls, and similar signaling or power-limited systems. The IRC addresses them in Chapter 43. The exam tests whether you can keep low-voltage wiring from being treated as ordinary Chapter 3 power wiring.
Core rules
- A Class 2 circuit must be supplied by a listed Class 2 power source. A transformer secondary is not automatically Class 2 unless it is listed and marked as such.
- Class 2 cable must be a listed type such as CL2, CL3, or PLTC, and it must be installed according to its listing and the applicable article.
- Class 2 conductors must not be installed in the same raceway, box, or enclosure with power or Class 1 conductors unless separated by a permanent barrier.
- Cable must be supported and secured as required, and it must not be used in place of Chapter 3 wiring methods for line-voltage circuits.
- In ducts, plenums, or other environmental air spaces, the cable must be rated for the location.
Worked example
A 24-volt doorbell cable enters a box that also contains 120-volt conductors. Is that permitted? Not unless a permanent barrier separates the Class 2 conductors from the power conductors. Simply twisting the wires or using a divider that can fall out does not satisfy the separation rule. The concern is insulation failure energizing the low-voltage system and its connected metal parts.
Traps
- Using CL2 cable for line-voltage control circuits.
- Mixing Class 2 and power conductors in one box without a barrier.
- Assuming any low-voltage transformer output is Class 2.
- Ignoring plenum and wet-location ratings.